Comparative Study of Conventional Ohmic and Hybrid Ohmic-Vacuum Heating for White Mulberry Syrup Concentration: Bioactive Compound Retention, Energy Consumption, and Multi-objective Optimization

Comparative Study of Conventional Ohmic and Hybrid Ohmic-Vacuum Heating for White Mulberry Syrup Concentration: Bioactive Compound Retention, Energy Consumption, and Multi-objective Optimization | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Comparative Study of Conventional Ohmic and Hybrid Ohmic-Vacuum Heating for White Mulberry Syrup Concentration: Bioactive Compound Retention, Energy Consumption, and Multi-objective Optimization Soraya Kakaeie, Mahmoud Koushesh Saba, Hosain Darvishi, Sirvan Mansouri This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8096105/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 14 You are reading this latest preprint version Abstract This study systematically compared conventional ohmic heating and hybrid ohmic-vacuum heating technologies for white mulberry syrup concentration, evaluating the interactive effects of voltage gradient (10–30 V/cm) and pressure (50–100 kPa) on bioactive compound retention, energy efficiency, and process optimization. Multi-objective optimization was performed using Non-dominated Sorting Genetic Algorithm II (NSGA-II) to simultaneously maximize bioactive compounds while minimizing processing time and energy consumption. Results demonstrated that increasing voltage gradient from 10 to 30 V/cm reduced processing time by 75.3% at atmospheric pressure, though ohmic-vacuum conditions exhibited 81–295% longer processing times due to reduced electrical conductivity at lower temperatures. Total phenolic content decreased by 28–48% across all treatments, with best retention (33.1 mg GAE/100 mL) achieved at 50 kPa and 10 V/cm. Antioxidant capacity showed excellent preservation (62.13–86.12%), peaking at 86.12% under intermediate conditions (75 kPa, 20 V/cm). Total flavonoid content exhibited dramatic variability (60.22–171.20 mg CE/100 g), with maximum retention at 50 kPa and 10 V/cm, while 20 V/cm proved universally detrimental regardless of pressure. Counterintuitively, conventional ohmic heating demonstrated superior energy efficiency, with specific energy consumption 2.5-3.7-fold lower than hybrid ohmic-vacuum method. NSGA-II optimization identified the best conditions at 83.47 kPa and 26.82 V/cm, which yielded the following experimental responses: 30.85 mg GAE/100 mL for total phenol content, 84.73% for antioxidant capacity, 78.14 mg CE/100 g for total flavonoid content, 12.24 min for processing time, and 2.87 MJ/kg water for energy consumption. Physical sciences/Chemistry Physical sciences/Engineering Biological sciences/Plant sciences Ohmic heating Vacuum concentration White mulberry syrup Bioactive compounds Energy consumption Multi-objective optimization Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction White mulberry (Morus alba L.) is a plant of significant agricultural and nutritional importance, traditionally cultivated for its leaves to feed silkworms but increasingly valued for its succulent and nutritious fruits. The berries are rich in bioactive compounds, including anthocyanins, flavonoids, and phenolic acids, which are associated with a range of health benefits such as antioxidant, anti-inflammatory, and anti-diabetic properties [ 1 ]. However, the high moisture content and delicate structure of fresh mulberries make them highly perishable, leading to substantial post-harvest losses and limiting their commercial shelf-life and distribution [ 2 ]. To overcome these limitations, the transformation of mulberries into stable products like concentrates and syrups is a common and effective practice. Concentration reduces water activity, inhibits microbial growth, and facilitates storage and transportation by reducing volume and weight [ 3 ]. Among conventional methods, thermal evaporation is the most widely used industrial technique. However, the application of prolonged high temperatures in such processes is a major drawback, often leading to the degradation of thermolabile nutrients [ 4 ], non-enzymatic browning [ 5 ], loss of volatile aroma compounds [ 6 ], and undesirable changes in color and flavor [ 7 ]. These detrimental effects ultimately compromise the sensory and nutritional quality of the final product, diminishing its market value and health-promoting potential [ 8 ]. In the quest for more efficient and gentle processing technologies, ohmic heating (OH) has emerged as a promising alternative to conventional methods. Ohmic heating, also known as Joule heating, is an electrothermal technique where an alternating electric current is passed directly through the food material, generating heat volumetrically due to its electrical resistance [ 9 ]. This internal generation of heat can result in rapid and uniform temperature distribution, minimizing thermal gradients and reducing the risk of localized overheating and burn-on, which are common in conventional heat exchangers [ 10 ]. Consequently, as demonstrated by researcher’s, OH can better preserve heat-sensitive compounds, leading to products with superior quality compared to those processed by conventional heating [ 11 ]. Despite its advantages, ohmic heating at atmospheric pressure still involves high temperatures that can, over time, affect sensitive components [ 12 ]. To further mitigate thermal damage, the combination of ohmic heating with vacuum concentration (VC) presents an innovative solution. Vacuum concentration lowers the boiling point of the liquid by reducing the operating pressure, thereby allowing evaporation to occur at significantly lower temperatures. The synergy of ohmic heating under vacuum—often termed Ohmic-Vacuum Concentration (OVC)—creates a highly efficient and mild processing environment [ 13 ]. The rapid and uniform heating of OH, coupled with the low-temperature evaporation of VC, holds great potential for maximizing the retention of bioactive compounds while simultaneously improving energy efficiency [ 14 ]. The energy efficiency arises from the direct energy transfer in OH, which avoids the heat transfer barriers of traditional heating surfaces, and the reduced latent heat of vaporization at lower pressures [ 15 ]. While the individual benefits of ohmic heating and vacuum concentration have been studied for various fruit juices, their combined application for the concentration of white mulberry syrup remains a relatively unexplored area. Therefore, the objectives of this study are to systematically investigate the Ohmic-Vacuum Concentration process for white mulberry syrup. This research aims to evaluate the effects of key process parameters on critical quality attributes—such as total phenolic content, antioxidant activity, and total flavonoid content—and on the specific energy consumption and processing time. Furthermore, the process will be optimized to identify the ideal operating conditions that achieve the desired concentration level while maximizing product quality and minimizing processing time and energy use, thereby contributing to the development of sustainable and high-quality food processing techniques. 2. Materials and methods 2.1 Sample Preparation Fresh mulberries were procured from a mulberry orchard located in Kermanshah Province, Iran, and immediately transported to the laboratory. Upon arrival, the fruits were stored at 4°C under refrigeration for approximately 8 h until experimental procedures commenced. The fresh mulberries were initially washed thoroughly with tap water to remove surface contaminants and debris. Following washing, the fruits were allowed to air-dry at ambient temperature for 15 min to remove excess surface moisture. The prepared mulberries were then homogenized using a fruit blender for 5 min to achieve complete tissue disruption. The resulting homogenate was filtered through a fine mesh to obtain a uniform juice consistency and remove particulate matter. To prepare the working sample for ohmic heating experiments, the fresh mulberry juice was diluted with distilled water at a ratio of 100 g juice to 25 mL water (4:1 w/v ratio), ensuring standardized initial conditions across all experimental treatments. 2.2. Ohmic Heating System The experimental apparatus (Fig. 1) consisted of a Pyrex glass cell equipped with two 316L stainless steel electrodes (150 mm × 100 mm × 1.5 mm). The ohmic cell was housed within a 4-liter vacuum chamber to ensure uniform pressure distribution across the sample and maintain safe operating conditions during reduced pressure treatments. The system was integrated with a voltage regulating transformer (1 kW, 0–330 V, 50 Hz, MST-3, Japan), a coated type-K thermocouple for temperature monitoring, and a power analyzer (Lutron DW-6090, Taiwan) for real-time electrical parameter measurements. The vacuum system comprised a piston dry vacuum pump (HL model, Guanyu, China), a buffer tank to minimize operational pulsations, and a condenser unit containing an ice-water mixture to recover evaporated water from the concentrated product. All process parameters including temperature, sample mass, current, and voltage were recorded at 1 s intervals using a PC-based data acquisition system. 2.3. Experimental Conditions Ohmic heating experiments were conducted under two distinct operational modes: (1) reduced pressure conditions (50 and 75 kPa absolute) and (2) atmospheric pressure (100 kPa), with each mode evaluated at three voltage gradients (10, 20, and 30 V/cm). Due to the laboratory's elevation of approximately 1459 meters above sea level, the atmospheric pressure was measured at less than 101.3 kPa, corresponding to a water boiling point of 92.7 ± 0.5°C. For each experimental run, approximately 150 g of prepared sample was transferred into the ohmic heating cell. Prior to treatment initiation, the vacuum pump was operated for 2 min to achieve stable vacuum conditions at the juice surface. The solution was concentrated to 60°Brix. consecutive experiments, the ohmic cell was thoroughly cleaned using distilled water and a soft brush to prevent cross-contamination and ensure consistent experimental conditions. 2.4. Specific Energy Consumption The specific energy consumption (SEC) for the ohmic heating concentration process was determined according to the methodology described by Cokgezme et al. (2017), as follows: $$\:\text{S}\text{E}\text{C}=\frac{\text{P}\times\:{\text{t}}_{\text{o}\text{n}}+\sum\:\left(\text{V}\text{I}\times\:\varDelta\:\text{t}\right)}{{\text{m}}_{\text{w}}}\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\left(1\right)$$ where SEC represents the specific energy consumption (J/kg water removed), P denotes the power consumption of the vacuum pump (W), t is the operational duration of the vacuum pump (s), V is the applied voltage (V), I is the current (A), Δt is the time interval (s), and mw is the mass of water evaporated (kg). The summation term accounts for the cumulative electrical energy delivered to the sample through ohmic heating. 2.5. Quality Assessment 2.5.1. Total Phenolic Content (TPC) Total phenolic content was determined using the Folin-Ciocalteu method [ 16 ]. Phenolic compounds were extracted from 0.5 mL of the sample by mixing with 2 mL of an ice-cold HCl-methanol-distilled water solution (1:80:19, v/v) and incubating for 12 h at 4°C. The mixture was then centrifuged at 12,000 × g for 10 min at 4°C to obtain the supernatant. An aliquot of the supernatant was reacted with the Folin-Ciocalteu reagent, and the absorbance was measured at 750 nm using a UV-Vis spectrophotometer (Unico UV-2100, USA). The TPC was calculated based on a gallic acid standard curve and expressed as mg of gallic acid equivalents per 100 mL of sample (mg GAE/100 mL). 2.5.2. Antioxidant Capacity (DPPH Assay) The antioxidant capacity was evaluated based on the scavenging activity of the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical, following the procedure of Sánchez-Moreno et al. (1999). The sample was mixed with a methanolic DPPH solution, and the reaction mixture was kept in the dark. After a set incubation period (e.g., 30 min), the absorbance was measured at 517 nm. The antioxidant capacity (AC) was calculated as a percentage of DPPH scavenging activity using the following formula: $$\:\text{A}\text{C}=\left(\frac{{\text{A}}_{\text{c}\text{o}\text{n}\text{t}\text{r}\text{o}\text{l}}-{\text{A}}_{\text{s}\text{a}\text{m}\text{p}\text{l}\text{e}}}{{\text{A}}_{\text{c}\text{o}\text{n}\text{t}\text{r}\text{o}\text{l}}}\:\right)\:\times\:100\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\left(2\right)$$ where A control ​ is the absorbance of the DPPH solution without the sample, and A sample ​ is the absorbance of the DPPH solution with the sample. 2.5.3. Total Flavonoid Content (TFC) The total flavonoid content was determined using the aluminum chloride colorimetric method as described by Zhishen et al. (1999). Briefly, 200 µL of the acid-methanol extract (prepared for TPC analysis) was mixed with 1280 µL of distilled water and 60 µL of sodium nitrite solution (5% w/v). After 5 min, 60 µL of aluminum chloride solution (10% w/v) was added. The mixture was allowed to stand for 6 min before 400 µL of sodium hydroxide solution (1 M) was added. The final solution was vortexed thoroughly, and after 5 min, the absorbance was measured at 510 nm against a prepared blank. The TFC was quantified using a catechin standard curve (0-500 ppm) and expressed as mg of catechin equivalents per 100 g of sample mass (mg CE/100 g). 2.6. Statistical analysis All experiments were conducted in triplicate. Results are presented as mean ± standard deviation (SD). The effect of drying conditions on selected properties was analyzed using univariate analysis of variance. Where ANOVA indicated significant differences (p ≤ 0.05), Duncan's multiple range test was applied for post-hoc mean comparison. Statistical analyses were performed using SPSS software (version 18.0). 2.7. Optimization Methodology The optimization of the ohmic-vacuum concentration process for white mulberry syrup was formulated as a multi-objective optimization (MOO) problem, aiming to simultaneously enhance product quality attributes while minimizing process inefficiencies. A Non-dominated Sorting Genetic Algorithm II (NSGA-II) was employed to address this complex optimization challenge due to its proven capability in handling competing objectives and generating diverse Pareto-optimal solutions. The independent variables consisted of system pressure (P: 50–100 kPa) and voltage gradient (∇V: 10–30 V/cm), while five critical response variables were evaluated and categorized into two groups based on optimization objectives. Quality attributes—total phenolic content (TPC, mg GAE/100 mL), antioxidant activity measured by DPPH radical scavenging assay (%), and total flavonoid content (TFC, mg CE/100 g)—were designated for maximization to ensure superior nutritional quality of the final concentrate. Process efficiency parameters—processing time (min) and specific energy consumption (SEC, MJ/kg water)—were targeted for minimization to achieve economically viable and sustainable industrial operation. Prior to optimization, mathematical modeling of the relationship between independent variables and each response was performed using TableCurve 3D software. This software systematically evaluated thousands of potential model equations, including polynomial, rational, logarithmic, and exponential functions, to identify the best-fit model for each response based on statistical criteria. Model selection was guided by three primary indicators: the coefficient of determination (R²) to assess the proportion of variance explained by the model, the fit standard error (FSR) to evaluate prediction accuracy, and the F-statistic to determine overall model significance. The NSGA-II algorithm was implemented with 100 chromosomes and 150 generations, using crossover rate of 0.8 and mutation rate of 0.2 to ensure robust convergence and solution diversity. Each chromosome encoded pressure and voltage gradient values within their feasible ranges. The evolutionary process began with random population initialization. In each generation, solutions were evaluated using five objective functions from regression models. Fast non-dominated sorting classified solutions into Pareto fronts based on dominance principles, where Pareto-optimal solutions represent trade-offs where no objective improves without compromising others. Crowding distance calculations-maintained diversity along the Pareto front. Binary tournament selection chose parents based on non-domination rank and crowding distance, while blend crossover and uniform mutation generated offspring. Min-max normalization scaled all objectives to [0,1] range, ensuring equal importance. For maximization objectives (TPC, DPPH, TFC), normalization used (Y-Ymin)/(Ymax -Ymin); for minimization objectives (Time, SEC), (Ymax-Y)/(Ymax -Ymin) was applied. The best compromise solution, identified by highest composite fitness value from the Pareto front, provided optimal operating conditions balancing bioactive retention and process efficiency. 3. Results and discussion 3.1. Thermal Behavior and Processing Time The thermal profiles of the juice sample during the ohmic heating-assisted concentration process are presented in Fig. 2 . Under conventional ohmic heating (100 kPa), the sample temperature reached a plateau of 86.5 ± 1.2°C. In contrast, under ohmic-vacuum conditions, the plateau temperature was much lower. It was 66.2 ± 1.0°C for 50 kPa and 76.5 ± 1.9°C for 75 kPa, meaning the temperature dropped by 10 to 20°C. This depression in the boiling point is a direct thermodynamic consequence of reduced pressure, a well-documented phenomenon that enhances the preservation of heat-sensitive compounds [ 17 ]. The results demonstrate a decrease in processing time (Fig. 3 ) as the voltage gradient increases across all pressure levels. For instance, at atmospheric pressure (100 kPa), elevating the voltage gradient from 10 V/cm to 30 V/cm caused the heating time to plummet from 31.23 min to just 7.70 min. This represents a dramatic 75.3% reduction in time. A similarly strong trend was observed at an intermediate vacuum of 75 kPa, where the time decreased from 33.15 min to 14.58 min, equating to a 56.0% reduction. Even under the strongest vacuum of 50 kPa, where the overall times were longer, increasing the voltage still yielded a 23.1% reduction from 39.55 min to 30.42 min. This powerful effect is a direct consequence of the principles of Joule heating. The thermal energy generated within the syrup is proportional to the square of the electric field strength (voltage gradient) [ 15 ]. Therefore, doubling the voltage gradient from 10 to 30 V/cm would theoretically quadruple the power input, leading to a much more rapid temperature rise and a consequent acceleration of water evaporation, thereby shortening the concentration time significantly [ 18 ]. At a constant voltage gradient, intensifying the vacuum (reducing pressure from 100 kPa to 50 kPa) consistently led to an increase in processing time. For example, at 30 V/cm, the time increased by 295% from 7.70 min at 100 kPa to 30.42 min at 50 kPa. The primary reason for this counter-intuitive trend lies in the interplay between vacuum and electrical conductivity. While a vacuum lowers the boiling point of the syrup—which is beneficial for preserving heat-sensitive compounds—it also results in a lower operating temperature. The electrical conductivity of ionic solutions like fruit syrup is highly temperature-dependent, decreasing as temperature drops [ 19 ]. This lower conductivity impedes the flow of electrical current, thereby reducing the rate of internal heat generation via ohmic heating [ 15 ]. This reduction in heating power outweighs the advantage of the lower boiling point, leading to a slower evaporation rate and a longer overall process [ 20 ]. 3.2. Total phenol content (TPC) The initial TPC of the fresh white mulberry sap was determined to be 46.2 mg GAE/100 mL. Following the ohmic-vacuum concentration process, a notable decrease in TPC was observed in all treated samples (Fig. 4), with values ranging from 24.2 to 33.1 mg GAE/100 mL. This represents a degradation of 28% to 48%, underscoring the susceptibility of phenolic compounds to the concentration process regardless of the processing conditions employed. The analysis of variance due to pressure and voltage gradient revealed a complex, non-linear interaction between these two factors. At the lowest pressure of 50 kPa, a clear decreasing trend in TPC was observed with increasing voltage gradient, declining from 33.1 mg GAE/100 mL at 10 V/cm to 32.4 mg GAE/100 mL at 20 V/cm, and further to 29.8 mg GAE/100 mL at 30 V/cm. This monotonic decrease suggests that while the reduced boiling point under vacuum conditions theoretically provides a protective environment for heat-sensitive phenolic compounds, this advantage is progressively offset by the intense and rapid heating generated at higher electrical fields [ 21 ]. The phenomenon of localized hot spots, which is inherent to ohmic heating technology, becomes increasingly pronounced at elevated voltage gradients, leading to severe thermal degradation of sensitive phenolics through accelerated oxidation reactions and the formation of degradation products [ 22 ]. The electrical field intensity at 30 V/cm appears to generate such rapid localized heating and higher electrochemical reaction that it overwhelms the beneficial effect of the lower boiling point provided by the vacuum environment. At a medium pressure of 75 kPa, the relationship between voltage gradient and TPC retention was notably less monotonic and revealed an interesting optimization window. The TPC was lowest at the minimal voltage gradient of 10 V/cm, measuring only 24.2 mg GAE/100 mL, which represents the poorest retention among all experimental conditions tested. This value then increased substantially to 31.5 mg GAE/100 mL at 20 V/cm before decreasing again to 28.2 mg GAE/100 mL at 30 V/cm. This non-linear pattern suggests a critical balance between thermal intensity and process duration, where both extremely slow and excessively fast heating rates lead to significant phenolic degradation [ 23 ]. The remarkably low TPC observed at 10 V/cm can be attributed to an extended exposure time to sub-boiling but still elevated temperatures, which allows for prolonged thermal degradation through cumulative oxidative damage. Despite the moderate vacuum level, the slow heating rate prolongs the time during which phenolic compounds are subjected to conditions conducive to degradation [ 24 ]. Conversely, the peak retention observed at 20 V/cm potentially represents an optimal processing window where the shorter process time, achieved through faster heating, effectively minimizes the overall thermal damage by reducing the exposure duration [ 25 ]. The subsequent decrease at 30 V/cm indicates that the heating rate has exceeded the optimal threshold, with excessive thermal power beginning to cause degradation through intense localized heating effects. The observed degradation of TPC (28–48%) aligns with studies on other fruits, though the extent varies. The non-linear interaction between pressure and voltage is a common finding. Similar to the work on grape juice concentration where higher voltages increased degradation due to electrochemical effects [ 23 ], our results show comparable trends. However, the optimal retention at a medium voltage (20 V/cm) and pressure (75 kPa) mirrors findings in black grape juice where moderate electrical fields best preserved phenolics [ 23 ], confirming that optimizing this balance is crucial for bioactive compound retention during ohmic-vacuum concentration. 3.3. Antioxidant Capacity (DPPH Assay) The DPPH radical scavenging activity data reveals distinct patterns influenced by voltage gradient and applied pressure during ohmic heating-vacuum concentration (Fig. 5). The results demonstrate values ranging from 62.13% to 86.12%, indicating substantial antioxidant capacity retention across various processing conditions. At low voltage gradient (10 V/cm), reducing pressure from atmospheric (100 kPa) to vacuum (50 kPa) increased antioxidant activity from 62.13% to 80.65%. This enhancement occurs because vacuum conditions lower the boiling point, enabling concentration at reduced temperatures [ 26 ]. Lower processing temperatures minimize thermal degradation of heat-sensitive antioxidant compounds such as flavonoids, anthocyanins, and phenolic acids [ 24 ]. Oxidative reactions catalyzed by elevated temperatures proceed more slowly under vacuum, preserving radical scavenging capacity [ 27 ]. Conversely, at moderate (20 V/cm) and high voltage gradients (30 V/cm), atmospheric pressure yielded superior antioxidant retention (85.01% and 82.63%, respectively) compared to vacuum conditions (68.16% and 68.09%). This reversal suggests that intense ohmic heating under vacuum creates unfavorable conditions. The combination of rapid heating and low pressure may accelerate volatile antioxidant loss through enhanced evaporation [ 28 ]. Additionally, structural disruption from aggressive heating potentially exposes antioxidants to oxidative damage despite reduced oxygen availability [ 29 ]. Under atmospheric pressure (100 kPa), increasing voltage gradient from 10 to 30 V/cm substantially improved antioxidant activity from 62.13% to 82.63%. Ohmic heating generates uniform internal heat through electrical resistance, minimizing temperature gradients that cause localized overheating [ 30 ]. Higher voltage gradients shorten processing time, reducing cumulative thermal exposure [ 31 ]. This rapid concentration preserves thermolabile antioxidants more effectively than prolonged gentle heating [ 32 ]. The electrical current may also enhance cell membrane permeabilization, facilitating antioxidant extraction from cellular matrices into the juice phase [ 33 ]. Under vacuum (50 kPa), voltage gradient effects proved negligible, with activities remaining relatively constant (80.65% at 10 V/cm, 68.09% at 30 V/cm, 68.16% at 20 V/cm). The pressure reduction dominates processing conditions, potentially masking voltage gradient benefits. Rapid evaporation under vacuum may limit the time-dependent advantages of faster heating rates. The intermediate condition (75 kPa, 20 V/cm) achieved the highest antioxidant retention (86.12%), followed closely by 75 kPa with 30 V/cm (85.04%). These results demonstrate synergistic effects between moderate vacuum and efficient ohmic heating. The moderate voltage gradient ensures rapid, uniform heating without the aggressive conditions that compromise antioxidant stability. The similar results were reported by Zandi et al. (2025) for concentration of black grape juice, Darvishi et al. (2021) for concentration of kiwi juice and Sofizadeh et al. (2023) for concentration of tomato juice. Fresh white mulberry juice typically exhibits high antioxidant activity due to intact cellular structures and unoxidized phenolic compounds. The processed samples achieving 85–86% activity demonstrate excellent preservation, suggesting minimal processing damage. The lowest value (62.13%) at atmospheric pressure with minimal heating represents suboptimal conditions where prolonged thermal exposure degrades antioxidants without vacuum protection. These findings confirm that properly optimized ohmic heating-vacuum concentration maintains antioxidant functionality comparable to fresh material, validating this technology for heat-sensitive fruit juice processing. In orange juice concentration, the ohmic-vacuum heating method resulted in a significantly lower reduction in antioxidant capacity compared to conventional methods [ 24 ]. For black grape juice, the highest antioxidant activity was achieved at 50 kPa and 10 V/cm, while increasing the voltage gradient to 30 V/cm led to a 35–40% reduction [ 23 ]. Similarly, in kiwifruit juice, concentrates produced under ohmic-vacuum conditions retained a higher antioxidant capacity (82.69–84.39%) than those under ohmic-atmospheric conditions (78.37–83.37%) [ 15 ]. In apple juice, ohmic evaporation better preserved total phenolic content and antioxidant activity compared to conventional heating [ 34 ]. For orange juice, the ohmic-vacuum concentration method resulted in significantly higher vitamin C retention than conventional methods [ 35 ]. 3.4. Total flavonoid content (TFC) According to Fig. 6 , the TFC of white mulberry syrup exhibited considerable variability in response to different combinations of voltage gradient (10–30 V/cm) and pressure (50–100 kPa) during ohmic heating-assisted vacuum concentration. TFC values ranged from 60.22 to 171.20 mg CE/100g, which shows that processing parameters strongly affect flavonoid preservation. At the lowest voltage gradient (10 V/cm), processing under atmospheric pressure (100 kPa) yielded a lower TFC (159.70 mg CE/100g) compared to vacuum conditions at 50 kPa (171.20 mg CE/100g). This pattern is ascribed to the protective influence of reduced pressure on thermally-labile flavonoids [ 36 ]. The vacuum environment substantially lowers the boiling point of water, facilitating concentration at diminished temperatures. This attenuated thermal load curtails the thermal degradation of flavonoids, which are prone to oxidative and structural deterioration at elevated temperatures [ 37 ]. The mild heating at 50 kPa, coupled with negligible electrical stress from the low voltage gradient, established an ideal setting for flavonoid conservation. Conversely, at atmospheric pressure, despite the low electrical intensity, the requisite higher processing temperature for evaporation prolonged the thermal exposure of flavonoids, instigating greater degradation via oxidative pathways and thermal decomposition [ 38 ]. TFC decreased markedly at 20 V/cm across all pressure levels, reaching a minimum of 62.72 mg CE/100g at 50 kPa and 60.22 mg CE/100g at 100 kPa. This drastic decline is explained by the synergistic deleterious effects of moderate electrical intensity and thermal stress [ 39 ]. This specific voltage level generates sufficient localized heating to accelerate detrimental chemical reactions, including flavonoid oxidation and polymerization, yet lacks the compensatory advantages of either very gentle heating (as at 10 V/cm) or ultra-rapid processing (as at 30 V/cm). The electric field at this intermediate level may also induce electrochemical reactions that potentiate flavonoid breakdown [ 40 ]. Furthermore, the moderate concentration rate likely prolongs the exposure duration to both thermal and electrical stresses, thereby maximizing degradation [ 41 ]. The comparable TFC values at both 50 and 100 kPa indicate that at this critical voltage, electrical stress overshadows the protective capacity of vacuum, becoming the predominant degradation factor. An intriguing reversal was observed at the highest voltage gradient (30 V/cm). Under atmospheric pressure (100 kPa), TFC increased to 142.21 mg CE/100g, whereas under vacuum (50 kPa), it decreased to 138.21 mg CE/100g. This counterintuitive phenomenon, where atmospheric pressure proved marginally superior, is elucidated by the expedited heating kinetics inherent to high voltage gradients. The intense, uniform volumetric heating drastically truncates the total processing time [ 42 ]. This severely limited exposure duration effectively preserves flavonoids by minimizing their time in degradative conditions [43]. At atmospheric pressure, although the temperature is higher, the extreme speed of the process sufficiently limits thermal damage [44]. Under vacuum at this high voltage, the confluence of reduced pressure and a strong electrical field may foster turbulent conditions through enhanced evaporation, potentially increasing oxygen contact and promoting oxidative degradation [ 15 ]. Analysis at an intermediate pressure of 75 kPa provided further insight into parameter interactions. At 10 V/cm and 75 kPa, a TFC of 115.71 mg CE/100g was recorded, intermediate to the values at 50 and 100 kPa, confirming a progressive pressure-related effect at low voltage. However, at 30 V/cm and 75 kPa, TFC fell sharply to 63.72 mg CE/100g, implying that intermediate pressure under high voltage creates suboptimal conditions, potentially due to an unstable vapor-liquid equilibrium favoring oxidation. At 20 V/cm and 75 kPa, a TFC of 82.31 mg CE/100g signified a partial recovery from the severe degradation seen at other pressures at this voltage, suggesting a modest protective effect of moderate vacuum, albeit insufficient to prevent major flavonoid loss. The identified trends elucidate the complex interplay between thermal degradation, electrochemical effects, processing duration, and oxygen availability. Low voltage gradients (10 V/cm) synergize with vacuum (50 kPa) to maximize TFC (171.20 mg CE/100g), while medium voltage gradients (20 V/cm) are profoundly detrimental irrespective of pressure, causing TFC to collapse below 63 mg CE/100g. High voltage gradients (30 V/cm) demonstrate that rapid processing, even at atmospheric pressure, can achieve respectable retention (142.21 mg CE/100g) by drastically minimizing exposure time, underscoring that processing duration can be as pivotal as temperature in determining the stability of bioactive compounds during thermal concentration [ 33 ]. 3.5. Specific energy Consumption The specific energy consumption (SEC) during ohmic-vacuum concentration of white mulberry juice was significantly influenced by the applied voltage gradient and system pressure (Fig. 7 ). The experimental data demonstrated a substantial 80% reduction in SEC, from 10.0 MJ/kg water evaporated at the lowest intensity (50 kPa, 10 V/cm) to 2.3 MJ/kg at the highest (100 kPa, 30 V/cm), underscoring the critical impact of parameter optimization on energy efficiency. The beneficial effect of increasing the voltage gradient on SEC was consistent across all pressure levels. At 50 kPa, increasing the gradient from 10 to 30 V/cm reduced SEC by 22% (10.0 to 7.8 MJ/kg water). This effect was more pronounced at 75 kPa, with a 59% reduction (7.9 to 3.2 MJ/kg water), and remained substantial at 100 kPa, showing a 43% decrease (3.5 to 2.3 MJ/kg water). This trend is strongly supported by the literature. Karakavuk et al. (2022) similarly observed a significant decrease in total energy consumption during the atmospheric ohmic evaporation of apple juice as the voltage gradient increased from 13 to 17 V/cm, attributing it to reduced processing times. The underlying mechanism is the principle of volumetric Joule heating, where the heat generation rate is proportional to the square of the electric field strength [45]. Higher voltage gradients accelerate ion mobility, thereby increasing the heating rate and shortening the process duration, which minimizes cumulative thermal losses [46]. A pivotal finding of this study was the superior energy efficiency of atmospheric pressure (100 kPa) operation compared to vacuum conditions, which contradicts conventional thermal processing wisdom. At 30 V/cm, SEC decreased progressively from 7.8 MJ/kg water at 50 kPa to 3.2 MJ/kg water at 75 kPa, and further to a minimum of 2.3 MJ/kg water at 100 kPa. This apparent paradox is resolved when considering the total system energy balance, including parasitic loads. Recent studies corroborate this finding. Mohammadi et al. (2025) reported that in vacuum ohmic systems, the energy consumed by the vacuum pump constituted 64.4–89.8% of the total energy input, making the process significantly more energy-intensive than atmospheric operation. Similarly, Darvishi et al. (2021), concentrating kiwifruit juice, found that energy consumption in ohmic-vacuum mode was 0.68–7.34 MJ/kg water higher than in ohmic-atmospheric mode, with the vacuum pump alone consuming 59–81% of the total energy. Thus, the theoretical energy benefit of a lower boiling point under vacuum is negated by the substantial auxiliary energy required to maintain the vacuum [ 15 ]. The processing time data, showing an 81% reduction from 39.55 min (50 kPa, 10 V/cm) to 7.70 min (100 kPa, 30 V/cm), strongly correlates with the SEC trends. Shorter processing times not only reduce energy input but also limit the thermal exposure of heat-sensitive compounds, conferring dual advantages of efficiency and quality preservation [47]. The best conditions identified in this study (100 kPa, 30 V/cm) achieved a minimum SEC of 2.30 MJ/kg. This result demonstrates a remarkable efficiency compared to conventional thermal evaporation. Darvishi et al. (2020), for instance, reported that the conventional concentration of black mulberry juice consumed 17.50 MJ/kg water, which is 4.7-fold higher than the maximum SEC they recorded for ohmic heating and 8.0-fold higher than the optimal SEC achieved in the present work. This difference highlights the profound energy-saving potential of optimized ohmic heating technology for fruit juice concentration. 3.6. Optimization and Validation The mathematical models presented in Table 1 , which exhibited high coefficients of determination (R² = 0.9357–0.9879), were employed as objective functions to predict system responses across the operational domain. The NSGA-II algorithm was configured with a population size of 100 chromosomes, operating over 150 generations with a crossover rate of 0.8 and a mutation rate of 0.2. Each chromosome encoded the two process parameters within their respective bounds, and fitness evaluation was performed by normalizing all five objective functions using min-max normalization to ensure equal weighting. The algorithm employed fast non-dominated sorting to classify solutions into Pareto fronts, with crowding distance calculations maintaining solution diversity throughout the evolutionary process. Binary tournament selection was utilized to choose parent chromosomes based on non-domination rank and crowding distance, while blend crossover and uniform mutation operators generated offspring populations. Table 1 Response models as a function of pressure and voltage gradient Response Model* R 2 FSR F-stat Time (min) \(\:\text{T}\text{i}\text{m}\text{e}=100.51-1.136\text{P}-1.898\nabla\:\text{V}+7.25\times\:{10}^{-3}{\text{P}}^{2}+0.0531{\nabla\:\text{V}}^{2}-0.0144\text{P}\times\:\nabla\:\text{V}\) 0.9879 2.034 48.89 SEC (MJ/kg water) \(\:\text{S}\text{E}\text{C}=26.71-0.321\text{P}-0.389\nabla\:\text{V}+1.22\times\:{10}^{-3}{\text{P}}^{2}+0.005{\nabla\:\text{V}}^{2}+0.0007\text{P}\times\:\nabla\:\text{V}\) 0.9499 1.121 11.38 DPPH (%) \(\:\text{A}\text{C}=77.30+\frac{3539}{\text{P}}-\frac{545.03}{\nabla\:\text{V}}-\frac{244800}{{\text{P}}^{2}}-\frac{2661}{{\nabla\:\text{V}}^{2}}+\frac{55244.5}{\text{P}\times\:\nabla\:\text{V}}\) 0.9413 3.484 9.621 TPC (mg GAE/100 mL) \(\:\text{T}\text{P}\text{C}=54.47-\frac{4284.6}{\text{P}}+\frac{210.5}{\nabla\:\text{V}}+\frac{121904}{{\text{P}}^{2}}-\frac{3201.7}{{\nabla\:\text{V}}^{2}}+\frac{13019.6}{\text{P}\times\:\nabla\:\text{V}}\) 0.9357 1.251 8.734 TFC (mg CE/100 g) \(\:\text{T}\text{F}\text{C}=\frac{63.94-3.56\text{P}+0.023{\text{P}}^{2}+18.62\text{l}\text{n}\text{P}}{1-0.040\nabla\:\text{V}+0.0003{\nabla\:\text{V}}^{2}+0.119\text{l}\text{n}\nabla\:\text{V}}\) 0.9862 10.391 23.900 Where, P is the pressure (kPa) and \(\:\nabla\:\text{V}\) is the voltage gradient (V/cm). The optimization convergence behavior demonstrated rapid improvement in the initial 80–100 generations, after which the best fitness value stabilized, indicating successful identification of the optimal region. The final Pareto front revealed inherent trade-offs between bioactive compound retention and process efficiency. Analysis of the non-dominated solutions showed that conditions favoring maximum bioactive preservation (low voltage gradient and reduced pressure) inevitably resulted in extended processing times and elevated energy consumption, whereas conditions optimizing process efficiency (high voltage gradient and atmospheric pressure) led to moderate reductions in certain bioactive compounds, particularly TFC. The algorithm identified the optimal operating conditions that provided the best compromise among all five objectives. The optimal parameters were determined to be P = 83.47 kPa and ∇V = 26.82 V/cm, yielding predicted responses of TPC = 30.85 mg GAE/100 mL, DPPH = 84.73%, TFC = 78.14 mg CE/100 g, processing time = 12.24 min, and SEC = 2.87 MJ/kg water. This solution achieved a composite fitness value of 0.782, representing an excellent balance between product quality and operational efficiency. To validate the optimization results, triplicate experimental runs were conducted at the predicted optimal conditions (P = 83.47 kPa, ∇V = 26.82 V/cm). The experimental values obtained were TPC = 30.01 ± 0.87 mg GAE/100 mL, DPPH = 85.38 ± 1.24%, TFC = 75.68 ± 3.45 mg CE/100 g, processing time = 11.85 ± 0.52 min, and SEC = 2.94 ± 0.15 MJ/kg water. Comparative analysis of the optimized conditions with individual optimal points for each response revealed the multi-objective nature of the problem. While 50 kPa and 10 V/cm provided maximum TPC (33.07 mg GAE/100 mL) and TFC (171.20 mg CE/100 g) retention, these conditions resulted in the longest processing time (39.55 min) and highest energy consumption (9.96 MJ/kg water), making them economically impractical for industrial-scale production. Conversely, 100 kPa and 30 V/cm achieved minimum processing time (7.70 min) and SEC (2.30 MJ/kg water) but with substantially reduced TFC (142.21 mg CE/100 g) compared to the gentlest conditions. The optimized solution at 83.47 kPa and 26.82 V/cm successfully balanced these competing objectives, retaining 91.3% of the maximum achievable TPC, 98.4% of peak antioxidant activity, while reducing processing time by 70.0% and energy consumption by 70.4% compared to the most quality-preserving conditions. The optimization results provide clear operational guidelines for industrial implementation based on production priorities. For premium, health-focused markets where bioactive compound retention is paramount, operating at 50 kPa and 10 V/cm maximizes nutritional quality despite elevated energy costs. For standard commercial production requiring a balance between quality and efficiency, the optimized conditions of approximately 75–85 kPa with 25–27 V/cm represent the ideal compromise, delivering excellent antioxidant capacity (> 84%), satisfactory phenolic retention (> 30 mg GAE/100 mL), rapid processing (< 13 min), and superior energy efficiency (< 3 MJ/kg water). For cost-driven industrial operations prioritizing throughput and minimal energy consumption, atmospheric pressure (100 kPa) with high voltage gradients (28–30 V/cm) offers the most economically viable solution while maintaining acceptable bioactive compound levels. These scientifically validated recommendations enable manufacturers to optimize their ohmic-vacuum concentration processes according to specific market requirements and economic constraints. Conclusion This study systematically evaluated conventional ohmic and hybrid ohmic-vacuum heating technologies for white mulberry syrup concentration, revealing critical trade-offs between bioactive compound retention and process efficiency. Increasing voltage gradient from 10 to 30 V/cm dramatically reduced processing time by 75.3% at atmospheric pressure, though vacuum conditions extended processing times by 81–295% due to reduced electrical conductivity at lower temperatures. Total phenolic content degradation ranged from 28–48%, with optimal retention (33.1 mg GAE/100 mL) at 50 kPa and 10 V/cm. Antioxidant capacity exhibited excellent preservation (62.13–86.12%), peaking at 86.12% under intermediate conditions (75 kPa, 20 V/cm). Total flavonoid content showed remarkable variability (60.22–171.20 mg CE/100 g), with 20 V/cm proving universally detrimental regardless of pressure. Counterintuitively, conventional ohmic heating demonstrated superior energy efficiency, consuming 2.5-3.7-fold less energy than hybrid ohmic-vacuum method due to substantial vacuum pump energy requirements. Multi-objective optimization using NSGA-II identified optimal conditions at 83.47 kPa and 26.82 V/cm, achieving an excellent compromise between bioactive retention and operational efficiency. These findings provide manufacturers with clear operational guidelines to select processing parameters based on product quality priorities versus cost-efficiency requirements, advancing sustainable food processing technologies. Declarations Competing interests The authors declare that they have no competing interests. Funding This research received no external funding. Author Contribution Soraya Kakaeie: Data curation; Methodology, Investigation.Hosain Darvishi: Supervision, Investigation, Writing – original draft.Mahmoud Koushesh Saba: Methodology, Writing – review & editing.Sirvan Mansouri: Investigation, Writing – review & editing. Data Availability The datasets used and/or analysed during the current study available from the corresponding author on reasonable request. References Alkanan, Z. T., Altemimi, A. B., Al-Hilphy, A. R., Cacciola, F. & Ibrahim, S. A. Application and effects of ohmic-vacuum combination heating on the quality factors of tomato paste. Foods, 10(12), p.2920. (2021). Astrain-Redin, L., Ospina, S., Cebrián, G. & Álvarez-Lanzarote, I. Ohmic heating technology for food applications, from ohmic systems to moderate electric fields and pulsed electric fields. Food Eng. Rev. 16 (2), 225–251 (2024). Athira, V. A. et al. Advances in drying techniques for retention of antioxidants in agro produces. Crit. Rev. Food Sci. Nutr. 63 (31), 10849–10865 (2023). Berk, E. & Gökmen, V. Evaporation in the fruit juice industry. In Evaporation Technology in Food Processing (105–136). Woodhead Publishing. (2024). Boateng, I. D. Recent processing of fruits and vegetables using emerging thermal and non-thermal technologies. A critical review of their potentialities and limitations on bioactives, structure, and drying performance. Crit. Rev. Food Sci. Nutr. 64 (13), 4240–4274 (2024). Bozkir, H. & Tekgül, Y. Production of orange juice concentrate using conventional and microwave vacuum evaporation: thermal degradation kinetics of bioactive compounds and color values. J. Food Process. Preserv. 46 (6), e15902 (2022). Cappato, L. P. et al. Ohmic heating in dairy processing: Relevant aspects for safety and quality Vol. 62, pp.104–112 (Trends in Food Science & Technology, 2017). Cokgezme, O. F., Sabanci, S., Cevik, M., Yildiz, H. & Icier, F. Performance analyses for evaporation of pomegranate juice in ohmic heating assisted vacuum system. J. Food Eng. 207 , 1–9 (2017). Croguennec, T. Non-enzymatic browning. Handbook of food science and technology 1: food alteration and food quality, pp.133–157. (2016). Darvishi, H., Behroozi-Khazaei, N., Saba, K., Alimohammadi, M., Nourbakhsh, H. & Z., & The influence of Ohmic-vacuum heating on phenol, ascorbic acid and engineering factors of kiwifruit juice concentration process. Int. J. Food Sci. Technol. 56 (9), 4789–4798 (2021). Darvishi, H., Mohammadi, P., Fadavi, A., Koushesh Saba, M. & Behroozi-Khazaei, N. Quality preservation of orange concentrate by using hybrid ohmic–vacuum heating. Food Chem. 289 , 292–298 (2019). Darvishi, H., Salami, P., Fadavi, A. & Saba, M. K. Processing kinetics, quality and thermodynamic evaluation of mulberry juice concentration process using Ohmic heating. Food Bioprod. Process. 123 , 102–110 (2020). Fadavi, A. & Salari, S. Ohmic heating of lemon and grapefruit juices under vacuum pressure—comparison of electrical conductivity and heating rate. J. Food Sci. 84 (10), 2868–2875 (2019). Fadavi, A., Yousefi, S., Darvishi, H. & Mirsaeedghazi, H. Comparative study of ohmic vacuum, ohmic, and conventional-vacuum heating methods on the quality of tomato concentrate Vol. 47, pp.225–230 (Innovative Food Science & Emerging Technologies, 2018). Gavahian, M. & Chu, R. Ohmic heating extraction at different times, temperatures, voltages, and frequencies: a new energy-saving technique for pineapple core valorization. Foods, 11(14), p.2015. (2022). Gundogdu, M., Canan, I., Gecer, M. K., Kan, T. & Ercisli, S. Phenolic compounds, bioactive content and antioxidant capacity of the fruits of mulberry (Morus spp.) germplasm in Turkey. Folia Horticulturae . 29 (2), 251–262 (2017). Hardinasinta, G., Mursalim, M., Muhidong, J. & Salengke, S. Degradation kinetics of anthocyanin, flavonoid, and total phenol in bignay (Antidesma bunius) fruit juice during ohmic heating. Food Sci. Technol. 42 , e64020 (2021). Hosainpour, A., Kheiralipour, K., Nadimi, M. & Paliwal, J. Quality assessment of dried white mulberry (Morus alba L.) using machine vision. Horticulturae, 8(11), p.1011. (2022). Hwang, J. H., Jung, A. H. & Park, S. H. Efficacy of Ohmic Vacuum Concentration for orange juice concentrates and their physicochemical properties under different voltage gradients. LWT - Food Sci. Technol. 154 , 112750 (2022). Ioannou, I., Chekir, L. & Ghoul, M. Effect of heat treatment and light exposure on the antioxidant activity of flavonoids. Processes, 8(9), p.1078. (2020). Ismail, M., Özbek, H. N. & Göğüş, F. Combined vacuum osmotic dehydration by pomegranate juice concentrate and hot-air assisted radiofrequency drying to produce fortified orange slices. Scientific Reports, 15(1), p.36001. (2025). Jaeger, H. et al. Opinion on the use of ohmic heating for the treatment of foods Vol. 55, pp.84–97 (Trends in Food Science & Technology, 2016). Karakavuk, E., Goksu, A. & Sabanci, S. Investigation of electrical conductivity and bioactive quality during ohmic evaporation process of Apple juice (Journal of Food Processing and Preservation, 2022). Kumar, A., Kumar, M., Mahboob, M. R. & Srivastava, B. Influence of° Brix/Acid, and flow rate of pineapple juice and electric field strength on the performance of continuous ohmic heating system. J. Food Sci. Technol. 61 (6), 1188–1200 (2024). Liu, Y. et al. Degradation of biochemical fractions in different temperature of food waste bioevaporation and their contribution to biogenerated heat. Journal of Cleaner Production, 245, p.118944. (2020). Nofiyanti, S. H., Fajarini, L. D. R., Putra, I. G. A. M. & Arista, Y. L. V. Process Intensification of Polyphenol and Flavonoid Extraction from Ant Nest (Myrmecodia pendans) via Ohmic Heating: Investigating Joule Heating and Electric Field-Time Interactions Using a Response Surface Methodology. Trends Sci. 22 (11), 10471–10471 (2025). Norouzi, S., Fadavi, A. & Darvishi, H. The ohmic and conventional heating methods in concentration of sour cherry juice: Quality and engineering factors. Journal of Food Engineering, 291, p.110242. (2021). Sabanci, S. & Icier, F. Applicability of ohmic heating assisted vacuum evaporation for concentration of sour cherry juice. J. Food Eng. 212 , 262–270 (2017). Sabanci, S., Cevik, M., Cokgezme, O. F., Yildiz, H. & Icier, F. Quality characteristics of pomegranate juice concentrates produced by ohmic heating assisted vacuum evaporation. J. Sci. Food. Agric. 99 (5), 2589–2595 (2019). Sain, M., Minz, P. S., John, H. & Singh, A. Effect of ohmic heating on food products: An in-depth review approach associated with quality attributes. J. Food Process. Preserv. 2024 (1), 2025937 (2024). Salari, S. & Jafari, S. M. The influence of ohmic heating on degradation of food bioactive ingredients. Food Eng. Rev. 12 (2), 191–208 (2020). Sánchez-Moreno, C., Larrauri, J. A. & Saura-Calixto, F. Free radical scavenging capacity and inhibition of lipid oxidation of wines, grape juices and related polyphenolic constituents. Food Res. Int. 32 (6), 407–412 (1999). Sastry, S. K., Heskitt, B. F., Sarang, S. S., Somavat, R. & Ayotte, K. Why ohmic heating? Advantages, applications, technology, and limitations. In Ohmic heating in food processing (Vol. 7, 7–16). Boca Raton: CRC. (2014). Singleton, V. L., Orthofer, R. & Lamuela-Raventos, R. M. Analysis of total phenols and other oxidation substrates and antioxidants by means of Folin–Ciocalteu, s reagent. Methods Enzymol. 299 , 152–178 (1999). Sofizadeh, T., Khodaei, J., Darvishi, H., Behroozi-Khazaei, N. & Koushesh Saba, M. Process parameters of microwave heating-assisted vacuum evaporation of tomato juice: quality, energy consumption, exergy performance, and kinetic processing. J. Microw. Power Electromagn. Energy. 57 (3), 203–218 (2023). Vahedi-Torshizi, M., Azadbakht, M. & Kashaninejad, M. Evaluation of the Effect of the Ohmic Process on the Physicochemical Properties of Sour Orange Juice Using Principal Component Analysis (PCA). Biosystems Eng. Renew. Energies . 1 (2), 106–114 (2025). Wani, M. Y. et al. The phenolic components extracted from mulberry fruits as bioactive compounds against cancer: A review. Phytother. Res. 37 (3), 1136–1152 (2023). Wu, B. et al. Effect of ultrasound-assisted vacuum far-infrared on the drying characteristics and qualities attributes of Cistanche slices. Agriculture, 14(4), p.557. (2024). Wu, W. et al. Effects of high pressure and thermal processing on quality properties and volatile compounds of pineapple fruit juice. Food Control, 130, p.108293. (2021). Zandi, N., Khodaei, J., Darvishi, H., Behroozi-Khazaei, N. & Koushesh Saba, M. Black Grape Juice Concentration via Ohmic-Vacuum Hybrid Heating: Quality Parameters, Energy Consumption and Exergy Efficiency. Innovative Food Technol. 12 (4), 321–337 (2025). Zhishen, J., Mengcheng, T. & Jianming, W. The determination of flavonoid contents in mulberry and their scavenging effects on superoxide radicals. Food Chem. 64 (4), 555–559 (1999). Zia, H., Slatnar, A., Košmerl, T. & Korošec, M. A review study on the effects of thermal and non-thermal processing techniques on the sensory properties of fruit juices and beverages. Front. Food Sci. Technol. 4 , 1405384 (2024). Additional Declarations No competing interests reported. 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system\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8096105/v1/3af0feb27b05a5f83ce1cc33.png"},{"id":102962863,"identity":"75d19502-0f9b-46b5-80c5-bf4e19a4cbc7","added_by":"auto","created_at":"2026-02-19 04:11:47","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":56884,"visible":true,"origin":"","legend":"\u003cp\u003eTemperature profile of white mulberry syrups during ohmic-vacuum concentration\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-8096105/v1/6763e3016b458e7c8826a66b.png"},{"id":102828863,"identity":"16ab3335-23a2-422b-a798-38495008ff70","added_by":"auto","created_at":"2026-02-17 09:26:35","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":54376,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of voltage gradient and pressure on processing time of whit mulberry syrups in ohmic heating system\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-8096105/v1/cdd7b95d5525477d1cf12d12.png"},{"id":102828902,"identity":"b75a388d-bad0-4b59-a277-8b75959a7125","added_by":"auto","created_at":"2026-02-17 09:26:39","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":43250,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of voltage gradient and pressure on total phenol content (TPC) of whit mulberry syrups\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-8096105/v1/59e401ab8133a9ca0eaf38b3.png"},{"id":102963613,"identity":"c9915df7-00a6-4e6c-b8ec-827a5a8a1fff","added_by":"auto","created_at":"2026-02-19 04:19:24","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":42097,"visible":true,"origin":"","legend":"\u003cp\u003eeffect of voltage gradient and pressure on antioxidant capacity (DPPH assay) of whit mulberry syrups\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-8096105/v1/c2082693586df99252d09e89.png"},{"id":102828921,"identity":"a969440a-5713-451a-a312-b9de3d938423","added_by":"auto","created_at":"2026-02-17 09:26:41","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":41673,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of voltage gradient and pressure on total flavonoid content (TFC) of whit mulberry syrups\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-8096105/v1/86287bfa937f7331eec4410f.png"},{"id":102828922,"identity":"629fae4e-b821-4836-ae68-c5c9d9d2a0f3","added_by":"auto","created_at":"2026-02-17 09:26:42","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":50521,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of voltage gradient and pressure on specific energy consumption (SEC) of whit mulberry syrups concentration process\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-8096105/v1/e473869627676d8aa58318ef.png"},{"id":103049777,"identity":"470a4841-c747-4275-b631-a15da8402166","added_by":"auto","created_at":"2026-02-20 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Introduction","content":"\u003cp\u003eWhite mulberry (Morus alba L.) is a plant of significant agricultural and nutritional importance, traditionally cultivated for its leaves to feed silkworms but increasingly valued for its succulent and nutritious fruits. The berries are rich in bioactive compounds, including anthocyanins, flavonoids, and phenolic acids, which are associated with a range of health benefits such as antioxidant, anti-inflammatory, and anti-diabetic properties [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. However, the high moisture content and delicate structure of fresh mulberries make them highly perishable, leading to substantial post-harvest losses and limiting their commercial shelf-life and distribution [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTo overcome these limitations, the transformation of mulberries into stable products like concentrates and syrups is a common and effective practice. Concentration reduces water activity, inhibits microbial growth, and facilitates storage and transportation by reducing volume and weight [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Among conventional methods, thermal evaporation is the most widely used industrial technique. However, the application of prolonged high temperatures in such processes is a major drawback, often leading to the degradation of thermolabile nutrients [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], non-enzymatic browning [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], loss of volatile aroma compounds [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], and undesirable changes in color and flavor [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. These detrimental effects ultimately compromise the sensory and nutritional quality of the final product, diminishing its market value and health-promoting potential [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn the quest for more efficient and gentle processing technologies, ohmic heating (OH) has emerged as a promising alternative to conventional methods. Ohmic heating, also known as Joule heating, is an electrothermal technique where an alternating electric current is passed directly through the food material, generating heat volumetrically due to its electrical resistance [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. This internal generation of heat can result in rapid and uniform temperature distribution, minimizing thermal gradients and reducing the risk of localized overheating and burn-on, which are common in conventional heat exchangers [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Consequently, as demonstrated by researcher\u0026rsquo;s, OH can better preserve heat-sensitive compounds, leading to products with superior quality compared to those processed by conventional heating [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eDespite its advantages, ohmic heating at atmospheric pressure still involves high temperatures that can, over time, affect sensitive components [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. To further mitigate thermal damage, the combination of ohmic heating with vacuum concentration (VC) presents an innovative solution. Vacuum concentration lowers the boiling point of the liquid by reducing the operating pressure, thereby allowing evaporation to occur at significantly lower temperatures. The synergy of ohmic heating under vacuum\u0026mdash;often termed Ohmic-Vacuum Concentration (OVC)\u0026mdash;creates a highly efficient and mild processing environment [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. The rapid and uniform heating of OH, coupled with the low-temperature evaporation of VC, holds great potential for maximizing the retention of bioactive compounds while simultaneously improving energy efficiency [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. The energy efficiency arises from the direct energy transfer in OH, which avoids the heat transfer barriers of traditional heating surfaces, and the reduced latent heat of vaporization at lower pressures [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eWhile the individual benefits of ohmic heating and vacuum concentration have been studied for various fruit juices, their combined application for the concentration of white mulberry syrup remains a relatively unexplored area. Therefore, the objectives of this study are to systematically investigate the Ohmic-Vacuum Concentration process for white mulberry syrup. This research aims to evaluate the effects of key process parameters on critical quality attributes\u0026mdash;such as total phenolic content, antioxidant activity, and total flavonoid content\u0026mdash;and on the specific energy consumption and processing time. Furthermore, the process will be optimized to identify the ideal operating conditions that achieve the desired concentration level while maximizing product quality and minimizing processing time and energy use, thereby contributing to the development of sustainable and high-quality food processing techniques.\u003c/p\u003e"},{"header":"2. Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Sample Preparation\u003c/h2\u003e \u003cp\u003eFresh mulberries were procured from a mulberry orchard located in Kermanshah Province, Iran, and immediately transported to the laboratory. Upon arrival, the fruits were stored at 4\u0026deg;C under refrigeration for approximately 8 h until experimental procedures commenced.\u003c/p\u003e \u003cp\u003eThe fresh mulberries were initially washed thoroughly with tap water to remove surface contaminants and debris. Following washing, the fruits were allowed to air-dry at ambient temperature for 15 min to remove excess surface moisture. The prepared mulberries were then homogenized using a fruit blender for 5 min to achieve complete tissue disruption. The resulting homogenate was filtered through a fine mesh to obtain a uniform juice consistency and remove particulate matter.\u003c/p\u003e \u003cp\u003eTo prepare the working sample for ohmic heating experiments, the fresh mulberry juice was diluted with distilled water at a ratio of 100 g juice to 25 mL water (4:1 w/v ratio), ensuring standardized initial conditions across all experimental treatments.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Ohmic Heating System\u003c/h2\u003e \u003cp\u003eThe experimental apparatus (Fig.\u0026nbsp;1) consisted of a Pyrex glass cell equipped with two 316L stainless steel electrodes (150 mm \u0026times; 100 mm \u0026times; 1.5 mm). The ohmic cell was housed within a 4-liter vacuum chamber to ensure uniform pressure distribution across the sample and maintain safe operating conditions during reduced pressure treatments. The system was integrated with a voltage regulating transformer (1 kW, 0\u0026ndash;330 V, 50 Hz, MST-3, Japan), a coated type-K thermocouple for temperature monitoring, and a power analyzer (Lutron DW-6090, Taiwan) for real-time electrical parameter measurements. The vacuum system comprised a piston dry vacuum pump (HL model, Guanyu, China), a buffer tank to minimize operational pulsations, and a condenser unit containing an ice-water mixture to recover evaporated water from the concentrated product. All process parameters including temperature, sample mass, current, and voltage were recorded at 1 s intervals using a PC-based data acquisition system.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Experimental Conditions\u003c/h2\u003e \u003cp\u003eOhmic heating experiments were conducted under two distinct operational modes: (1) reduced pressure conditions (50 and 75 kPa absolute) and (2) atmospheric pressure (100 kPa), with each mode evaluated at three voltage gradients (10, 20, and 30 V/cm). Due to the laboratory's elevation of approximately 1459 meters above sea level, the atmospheric pressure was measured at less than 101.3 kPa, corresponding to a water boiling point of 92.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u0026deg;C.\u003c/p\u003e \u003cp\u003eFor each experimental run, approximately 150 g of prepared sample was transferred into the ohmic heating cell. Prior to treatment initiation, the vacuum pump was operated for 2 min to achieve stable vacuum conditions at the juice surface. The solution was concentrated to 60\u0026deg;Brix. consecutive experiments, the ohmic cell was thoroughly cleaned using distilled water and a soft brush to prevent cross-contamination and ensure consistent experimental conditions.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4. Specific Energy Consumption\u003c/h2\u003e \u003cp\u003eThe specific energy consumption (SEC) for the ohmic heating concentration process was determined according to the methodology described by Cokgezme et al. (2017), as follows:\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:\\text{S}\\text{E}\\text{C}=\\frac{\\text{P}\\times\\:{\\text{t}}_{\\text{o}\\text{n}}+\\sum\\:\\left(\\text{V}\\text{I}\\times\\:\\varDelta\\:\\text{t}\\right)}{{\\text{m}}_{\\text{w}}}\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\left(1\\right)$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere SEC represents the specific energy consumption (J/kg water removed), P denotes the power consumption of the vacuum pump (W), t is the operational duration of the vacuum pump (s), V is the applied voltage (V), I is the current (A), Δt is the time interval (s), and mw is the mass of water evaporated (kg). The summation term accounts for the cumulative electrical energy delivered to the sample through ohmic heating.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5. Quality Assessment\u003c/h2\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003e2.5.1. Total Phenolic Content (TPC)\u003c/h2\u003e \u003cp\u003eTotal phenolic content was determined using the Folin-Ciocalteu method [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Phenolic compounds were extracted from 0.5 mL of the sample by mixing with 2 mL of an ice-cold HCl-methanol-distilled water solution (1:80:19, v/v) and incubating for 12 h at 4\u0026deg;C. The mixture was then centrifuged at 12,000 \u0026times; g for 10 min at 4\u0026deg;C to obtain the supernatant. An aliquot of the supernatant was reacted with the Folin-Ciocalteu reagent, and the absorbance was measured at 750 nm using a UV-Vis spectrophotometer (Unico UV-2100, USA). The TPC was calculated based on a gallic acid standard curve and expressed as mg of gallic acid equivalents per 100 mL of sample (mg GAE/100 mL).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e2.5.2. Antioxidant Capacity (DPPH Assay)\u003c/h2\u003e \u003cp\u003eThe antioxidant capacity was evaluated based on the scavenging activity of the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical, following the procedure of S\u0026aacute;nchez-Moreno et al. (1999). The sample was mixed with a methanolic DPPH solution, and the reaction mixture was kept in the dark. After a set incubation period (e.g., 30 min), the absorbance was measured at 517 nm. The antioxidant capacity (AC) was calculated as a percentage of DPPH scavenging activity using the following formula:\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e\n$$\\:\\text{A}\\text{C}=\\left(\\frac{{\\text{A}}_{\\text{c}\\text{o}\\text{n}\\text{t}\\text{r}\\text{o}\\text{l}}-{\\text{A}}_{\\text{s}\\text{a}\\text{m}\\text{p}\\text{l}\\text{e}}}{{\\text{A}}_{\\text{c}\\text{o}\\text{n}\\text{t}\\text{r}\\text{o}\\text{l}}}\\:\\right)\\:\\times\\:100\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\left(2\\right)$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere A\u003csub\u003econtrol\u003c/sub\u003e​ is the absorbance of the DPPH solution without the sample, and A\u003csub\u003esample\u003c/sub\u003e​ is the absorbance of the DPPH solution with the sample.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003e2.5.3. Total Flavonoid Content (TFC)\u003c/h2\u003e \u003cp\u003eThe total flavonoid content was determined using the aluminum chloride colorimetric method as described by Zhishen et al. (1999). Briefly, 200 \u0026micro;L of the acid-methanol extract (prepared for TPC analysis) was mixed with 1280 \u0026micro;L of distilled water and 60 \u0026micro;L of sodium nitrite solution (5% w/v). After 5 min, 60 \u0026micro;L of aluminum chloride solution (10% w/v) was added. The mixture was allowed to stand for 6 min before 400 \u0026micro;L of sodium hydroxide solution (1 M) was added. The final solution was vortexed thoroughly, and after 5 min, the absorbance was measured at 510 nm against a prepared blank. The TFC was quantified using a catechin standard curve (0-500 ppm) and expressed as mg of catechin equivalents per 100 g of sample mass (mg CE/100 g).\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e2.6. Statistical analysis\u003c/h2\u003e \u003cp\u003eAll experiments were conducted in triplicate. Results are presented as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation (SD). The effect of drying conditions on selected properties was analyzed using univariate analysis of variance. Where ANOVA indicated significant differences (p\u0026thinsp;\u0026le;\u0026thinsp;0.05), Duncan's multiple range test was applied for post-hoc mean comparison. Statistical analyses were performed using SPSS software (version 18.0).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e2.7. Optimization Methodology\u003c/h2\u003e \u003cp\u003eThe optimization of the ohmic-vacuum concentration process for white mulberry syrup was formulated as a multi-objective optimization (MOO) problem, aiming to simultaneously enhance product quality attributes while minimizing process inefficiencies. A Non-dominated Sorting Genetic Algorithm II (NSGA-II) was employed to address this complex optimization challenge due to its proven capability in handling competing objectives and generating diverse Pareto-optimal solutions. The independent variables consisted of system pressure (P: 50\u0026ndash;100 kPa) and voltage gradient (\u0026nabla;V: 10\u0026ndash;30 V/cm), while five critical response variables were evaluated and categorized into two groups based on optimization objectives. Quality attributes\u0026mdash;total phenolic content (TPC, mg GAE/100 mL), antioxidant activity measured by DPPH radical scavenging assay (%), and total flavonoid content (TFC, mg CE/100 g)\u0026mdash;were designated for maximization to ensure superior nutritional quality of the final concentrate. Process efficiency parameters\u0026mdash;processing time (min) and specific energy consumption (SEC, MJ/kg water)\u0026mdash;were targeted for minimization to achieve economically viable and sustainable industrial operation.\u003c/p\u003e \u003cp\u003ePrior to optimization, mathematical modeling of the relationship between independent variables and each response was performed using TableCurve 3D software. This software systematically evaluated thousands of potential model equations, including polynomial, rational, logarithmic, and exponential functions, to identify the best-fit model for each response based on statistical criteria. Model selection was guided by three primary indicators: the coefficient of determination (R\u0026sup2;) to assess the proportion of variance explained by the model, the fit standard error (FSR) to evaluate prediction accuracy, and the F-statistic to determine overall model significance. The NSGA-II algorithm was implemented with 100 chromosomes and 150 generations, using crossover rate of 0.8 and mutation rate of 0.2 to ensure robust convergence and solution diversity. Each chromosome encoded pressure and voltage gradient values within their feasible ranges.\u003c/p\u003e \u003cp\u003eThe evolutionary process began with random population initialization. In each generation, solutions were evaluated using five objective functions from regression models. Fast non-dominated sorting classified solutions into Pareto fronts based on dominance principles, where Pareto-optimal solutions represent trade-offs where no objective improves without compromising others. Crowding distance calculations-maintained diversity along the Pareto front. Binary tournament selection chose parents based on non-domination rank and crowding distance, while blend crossover and uniform mutation generated offspring.\u003c/p\u003e \u003cp\u003eMin-max normalization scaled all objectives to [0,1] range, ensuring equal importance. For maximization objectives (TPC, DPPH, TFC), normalization used (Y-Ymin)/(Ymax -Ymin); for minimization objectives (Time, SEC), (Ymax-Y)/(Ymax -Ymin) was applied. The best compromise solution, identified by highest composite fitness value from the Pareto front, provided optimal operating conditions balancing bioactive retention and process efficiency.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Thermal Behavior and Processing Time\u003c/h2\u003e \u003cp\u003eThe thermal profiles of the juice sample during the ohmic heating-assisted concentration process are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Under conventional ohmic heating (100 kPa), the sample temperature reached a plateau of 86.5\u0026thinsp;\u0026plusmn;\u0026thinsp;1.2\u0026deg;C. In contrast, under ohmic-vacuum conditions, the plateau temperature was much lower. It was 66.2\u0026thinsp;\u0026plusmn;\u0026thinsp;1.0\u0026deg;C for 50 kPa and 76.5\u0026thinsp;\u0026plusmn;\u0026thinsp;1.9\u0026deg;C for 75 kPa, meaning the temperature dropped by 10 to 20\u0026deg;C. This depression in the boiling point is a direct thermodynamic consequence of reduced pressure, a well-documented phenomenon that enhances the preservation of heat-sensitive compounds [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe results demonstrate a decrease in processing time (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003e) as the voltage gradient increases across all pressure levels. For instance, at atmospheric pressure (100 kPa), elevating the voltage gradient from 10 V/cm to 30 V/cm caused the heating time to plummet from 31.23 min to just 7.70 min. This represents a dramatic 75.3% reduction in time. A similarly strong trend was observed at an intermediate vacuum of 75 kPa, where the time decreased from 33.15 min to 14.58 min, equating to a 56.0% reduction. Even under the strongest vacuum of 50 kPa, where the overall times were longer, increasing the voltage still yielded a 23.1% reduction from 39.55 min to 30.42 min. This powerful effect is a direct consequence of the principles of Joule heating. The thermal energy generated within the syrup is proportional to the square of the electric field strength (voltage gradient) [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Therefore, doubling the voltage gradient from 10 to 30 V/cm would theoretically quadruple the power input, leading to a much more rapid temperature rise and a consequent acceleration of water evaporation, thereby shortening the concentration time significantly [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAt a constant voltage gradient, intensifying the vacuum (reducing pressure from 100 kPa to 50 kPa) consistently led to an increase in processing time. For example, at 30 V/cm, the time increased by 295% from 7.70 min at 100 kPa to 30.42 min at 50 kPa. The primary reason for this counter-intuitive trend lies in the interplay between vacuum and electrical conductivity. While a vacuum lowers the boiling point of the syrup\u0026mdash;which is beneficial for preserving heat-sensitive compounds\u0026mdash;it also results in a lower operating temperature. The electrical conductivity of ionic solutions like fruit syrup is highly temperature-dependent, decreasing as temperature drops [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. This lower conductivity impedes the flow of electrical current, thereby reducing the rate of internal heat generation via ohmic heating [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. This reduction in heating power outweighs the advantage of the lower boiling point, leading to a slower evaporation rate and a longer overall process [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Total phenol content (TPC)\u003c/h2\u003e \u003cp\u003eThe initial TPC of the fresh white mulberry sap was determined to be 46.2 mg GAE/100 mL. Following the ohmic-vacuum concentration process, a notable decrease in TPC was observed in all treated samples (Fig.\u0026nbsp;4), with values ranging from 24.2 to 33.1 mg GAE/100 mL. This represents a degradation of 28% to 48%, underscoring the susceptibility of phenolic compounds to the concentration process regardless of the processing conditions employed. The analysis of variance due to pressure and voltage gradient revealed a complex, non-linear interaction between these two factors. At the lowest pressure of 50 kPa, a clear decreasing trend in TPC was observed with increasing voltage gradient, declining from 33.1 mg GAE/100 mL at 10 V/cm to 32.4 mg GAE/100 mL at 20 V/cm, and further to 29.8 mg GAE/100 mL at 30 V/cm. This monotonic decrease suggests that while the reduced boiling point under vacuum conditions theoretically provides a protective environment for heat-sensitive phenolic compounds, this advantage is progressively offset by the intense and rapid heating generated at higher electrical fields [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. The phenomenon of localized hot spots, which is inherent to ohmic heating technology, becomes increasingly pronounced at elevated voltage gradients, leading to severe thermal degradation of sensitive phenolics through accelerated oxidation reactions and the formation of degradation products [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. The electrical field intensity at 30 V/cm appears to generate such rapid localized heating and higher electrochemical reaction that it overwhelms the beneficial effect of the lower boiling point provided by the vacuum environment.\u003c/p\u003e \u003cp\u003eAt a medium pressure of 75 kPa, the relationship between voltage gradient and TPC retention was notably less monotonic and revealed an interesting optimization window. The TPC was lowest at the minimal voltage gradient of 10 V/cm, measuring only 24.2 mg GAE/100 mL, which represents the poorest retention among all experimental conditions tested. This value then increased substantially to 31.5 mg GAE/100 mL at 20 V/cm before decreasing again to 28.2 mg GAE/100 mL at 30 V/cm. This non-linear pattern suggests a critical balance between thermal intensity and process duration, where both extremely slow and excessively fast heating rates lead to significant phenolic degradation [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. The remarkably low TPC observed at 10 V/cm can be attributed to an extended exposure time to sub-boiling but still elevated temperatures, which allows for prolonged thermal degradation through cumulative oxidative damage. Despite the moderate vacuum level, the slow heating rate prolongs the time during which phenolic compounds are subjected to conditions conducive to degradation [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Conversely, the peak retention observed at 20 V/cm potentially represents an optimal processing window where the shorter process time, achieved through faster heating, effectively minimizes the overall thermal damage by reducing the exposure duration [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. The subsequent decrease at 30 V/cm indicates that the heating rate has exceeded the optimal threshold, with excessive thermal power beginning to cause degradation through intense localized heating effects.\u003c/p\u003e \u003cp\u003eThe observed degradation of TPC (28\u0026ndash;48%) aligns with studies on other fruits, though the extent varies. The non-linear interaction between pressure and voltage is a common finding. Similar to the work on grape juice concentration where higher voltages increased degradation due to electrochemical effects [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e], our results show comparable trends. However, the optimal retention at a medium voltage (20 V/cm) and pressure (75 kPa) mirrors findings in black grape juice where moderate electrical fields best preserved phenolics [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e], confirming that optimizing this balance is crucial for bioactive compound retention during ohmic-vacuum concentration.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003e3.3. Antioxidant Capacity (DPPH Assay)\u003c/h2\u003e \u003cp\u003eThe DPPH radical scavenging activity data reveals distinct patterns influenced by voltage gradient and applied pressure during ohmic heating-vacuum concentration (Fig.\u0026nbsp;5). The results demonstrate values ranging from 62.13% to 86.12%, indicating substantial antioxidant capacity retention across various processing conditions. At low voltage gradient (10 V/cm), reducing pressure from atmospheric (100 kPa) to vacuum (50 kPa) increased antioxidant activity from 62.13% to 80.65%. This enhancement occurs because vacuum conditions lower the boiling point, enabling concentration at reduced temperatures [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Lower processing temperatures minimize thermal degradation of heat-sensitive antioxidant compounds such as flavonoids, anthocyanins, and phenolic acids [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Oxidative reactions catalyzed by elevated temperatures proceed more slowly under vacuum, preserving radical scavenging capacity [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eConversely, at moderate (20 V/cm) and high voltage gradients (30 V/cm), atmospheric pressure yielded superior antioxidant retention (85.01% and 82.63%, respectively) compared to vacuum conditions (68.16% and 68.09%). This reversal suggests that intense ohmic heating under vacuum creates unfavorable conditions. The combination of rapid heating and low pressure may accelerate volatile antioxidant loss through enhanced evaporation [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. Additionally, structural disruption from aggressive heating potentially exposes antioxidants to oxidative damage despite reduced oxygen availability [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eUnder atmospheric pressure (100 kPa), increasing voltage gradient from 10 to 30 V/cm substantially improved antioxidant activity from 62.13% to 82.63%. Ohmic heating generates uniform internal heat through electrical resistance, minimizing temperature gradients that cause localized overheating [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. Higher voltage gradients shorten processing time, reducing cumulative thermal exposure [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. This rapid concentration preserves thermolabile antioxidants more effectively than prolonged gentle heating [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. The electrical current may also enhance cell membrane permeabilization, facilitating antioxidant extraction from cellular matrices into the juice phase [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eUnder vacuum (50 kPa), voltage gradient effects proved negligible, with activities remaining relatively constant (80.65% at 10 V/cm, 68.09% at 30 V/cm, 68.16% at 20 V/cm). The pressure reduction dominates processing conditions, potentially masking voltage gradient benefits. Rapid evaporation under vacuum may limit the time-dependent advantages of faster heating rates.\u003c/p\u003e \u003cp\u003eThe intermediate condition (75 kPa, 20 V/cm) achieved the highest antioxidant retention (86.12%), followed closely by 75 kPa with 30 V/cm (85.04%). These results demonstrate synergistic effects between moderate vacuum and efficient ohmic heating. The moderate voltage gradient ensures rapid, uniform heating without the aggressive conditions that compromise antioxidant stability. The similar results were reported by Zandi et al. (2025) for concentration of black grape juice, Darvishi et al. (2021) for concentration of kiwi juice and Sofizadeh et al. (2023) for concentration of tomato juice.\u003c/p\u003e \u003cp\u003eFresh white mulberry juice typically exhibits high antioxidant activity due to intact cellular structures and unoxidized phenolic compounds. The processed samples achieving 85\u0026ndash;86% activity demonstrate excellent preservation, suggesting minimal processing damage. The lowest value (62.13%) at atmospheric pressure with minimal heating represents suboptimal conditions where prolonged thermal exposure degrades antioxidants without vacuum protection. These findings confirm that properly optimized ohmic heating-vacuum concentration maintains antioxidant functionality comparable to fresh material, validating this technology for heat-sensitive fruit juice processing. In orange juice concentration, the ohmic-vacuum heating method resulted in a significantly lower reduction in antioxidant capacity compared to conventional methods [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. For black grape juice, the highest antioxidant activity was achieved at 50 kPa and 10 V/cm, while increasing the voltage gradient to 30 V/cm led to a 35\u0026ndash;40% reduction [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Similarly, in kiwifruit juice, concentrates produced under ohmic-vacuum conditions retained a higher antioxidant capacity (82.69\u0026ndash;84.39%) than those under ohmic-atmospheric conditions (78.37\u0026ndash;83.37%) [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. In apple juice, ohmic evaporation better preserved total phenolic content and antioxidant activity compared to conventional heating [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. For orange juice, the ohmic-vacuum concentration method resulted in significantly higher vitamin C retention than conventional methods [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003e3.4. Total flavonoid content (TFC)\u003c/h2\u003e \u003cp\u003eAccording to Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e6\u003c/span\u003e, the TFC of white mulberry syrup exhibited considerable variability in response to different combinations of voltage gradient (10\u0026ndash;30 V/cm) and pressure (50\u0026ndash;100 kPa) during ohmic heating-assisted vacuum concentration. TFC values ranged from 60.22 to 171.20 mg CE/100g, which shows that processing parameters strongly affect flavonoid preservation. At the lowest voltage gradient (10 V/cm), processing under atmospheric pressure (100 kPa) yielded a lower TFC (159.70 mg CE/100g) compared to vacuum conditions at 50 kPa (171.20 mg CE/100g). This pattern is ascribed to the protective influence of reduced pressure on thermally-labile flavonoids [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. The vacuum environment substantially lowers the boiling point of water, facilitating concentration at diminished temperatures. This attenuated thermal load curtails the thermal degradation of flavonoids, which are prone to oxidative and structural deterioration at elevated temperatures [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. The mild heating at 50 kPa, coupled with negligible electrical stress from the low voltage gradient, established an ideal setting for flavonoid conservation. Conversely, at atmospheric pressure, despite the low electrical intensity, the requisite higher processing temperature for evaporation prolonged the thermal exposure of flavonoids, instigating greater degradation via oxidative pathways and thermal decomposition [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTFC decreased markedly at 20 V/cm across all pressure levels, reaching a minimum of 62.72 mg CE/100g at 50 kPa and 60.22 mg CE/100g at 100 kPa. This drastic decline is explained by the synergistic deleterious effects of moderate electrical intensity and thermal stress [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. This specific voltage level generates sufficient localized heating to accelerate detrimental chemical reactions, including flavonoid oxidation and polymerization, yet lacks the compensatory advantages of either very gentle heating (as at 10 V/cm) or ultra-rapid processing (as at 30 V/cm). The electric field at this intermediate level may also induce electrochemical reactions that potentiate flavonoid breakdown [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]. Furthermore, the moderate concentration rate likely prolongs the exposure duration to both thermal and electrical stresses, thereby maximizing degradation [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. The comparable TFC values at both 50 and 100 kPa indicate that at this critical voltage, electrical stress overshadows the protective capacity of vacuum, becoming the predominant degradation factor.\u003c/p\u003e \u003cp\u003eAn intriguing reversal was observed at the highest voltage gradient (30 V/cm). Under atmospheric pressure (100 kPa), TFC increased to 142.21 mg CE/100g, whereas under vacuum (50 kPa), it decreased to 138.21 mg CE/100g. This counterintuitive phenomenon, where atmospheric pressure proved marginally superior, is elucidated by the expedited heating kinetics inherent to high voltage gradients. The intense, uniform volumetric heating drastically truncates the total processing time [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]. This severely limited exposure duration effectively preserves flavonoids by minimizing their time in degradative conditions [43]. At atmospheric pressure, although the temperature is higher, the extreme speed of the process sufficiently limits thermal damage [44]. Under vacuum at this high voltage, the confluence of reduced pressure and a strong electrical field may foster turbulent conditions through enhanced evaporation, potentially increasing oxygen contact and promoting oxidative degradation [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAnalysis at an intermediate pressure of 75 kPa provided further insight into parameter interactions. At 10 V/cm and 75 kPa, a TFC of 115.71 mg CE/100g was recorded, intermediate to the values at 50 and 100 kPa, confirming a progressive pressure-related effect at low voltage. However, at 30 V/cm and 75 kPa, TFC fell sharply to 63.72 mg CE/100g, implying that intermediate pressure under high voltage creates suboptimal conditions, potentially due to an unstable vapor-liquid equilibrium favoring oxidation. At 20 V/cm and 75 kPa, a TFC of 82.31 mg CE/100g signified a partial recovery from the severe degradation seen at other pressures at this voltage, suggesting a modest protective effect of moderate vacuum, albeit insufficient to prevent major flavonoid loss.\u003c/p\u003e \u003cp\u003eThe identified trends elucidate the complex interplay between thermal degradation, electrochemical effects, processing duration, and oxygen availability. Low voltage gradients (10 V/cm) synergize with vacuum (50 kPa) to maximize TFC (171.20 mg CE/100g), while medium voltage gradients (20 V/cm) are profoundly detrimental irrespective of pressure, causing TFC to collapse below 63 mg CE/100g. High voltage gradients (30 V/cm) demonstrate that rapid processing, even at atmospheric pressure, can achieve respectable retention (142.21 mg CE/100g) by drastically minimizing exposure time, underscoring that processing duration can be as pivotal as temperature in determining the stability of bioactive compounds during thermal concentration [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e3.5. Specific energy Consumption\u003c/h2\u003e \u003cp\u003eThe specific energy consumption (SEC) during ohmic-vacuum concentration of white mulberry juice was significantly influenced by the applied voltage gradient and system pressure (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e7\u003c/span\u003e). The experimental data demonstrated a substantial 80% reduction in SEC, from 10.0 MJ/kg water evaporated at the lowest intensity (50 kPa, 10 V/cm) to 2.3 MJ/kg at the highest (100 kPa, 30 V/cm), underscoring the critical impact of parameter optimization on energy efficiency.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe beneficial effect of increasing the voltage gradient on SEC was consistent across all pressure levels. At 50 kPa, increasing the gradient from 10 to 30 V/cm reduced SEC by 22% (10.0 to 7.8 MJ/kg water). This effect was more pronounced at 75 kPa, with a 59% reduction (7.9 to 3.2 MJ/kg water), and remained substantial at 100 kPa, showing a 43% decrease (3.5 to 2.3 MJ/kg water). This trend is strongly supported by the literature. Karakavuk et al. (2022) similarly observed a significant decrease in total energy consumption during the atmospheric ohmic evaporation of apple juice as the voltage gradient increased from 13 to 17 V/cm, attributing it to reduced processing times. The underlying mechanism is the principle of volumetric Joule heating, where the heat generation rate is proportional to the square of the electric field strength [45]. Higher voltage gradients accelerate ion mobility, thereby increasing the heating rate and shortening the process duration, which minimizes cumulative thermal losses [46].\u003c/p\u003e \u003cp\u003eA pivotal finding of this study was the superior energy efficiency of atmospheric pressure (100 kPa) operation compared to vacuum conditions, which contradicts conventional thermal processing wisdom. At 30 V/cm, SEC decreased progressively from 7.8 MJ/kg water at 50 kPa to 3.2 MJ/kg water at 75 kPa, and further to a minimum of 2.3 MJ/kg water at 100 kPa. This apparent paradox is resolved when considering the total system energy balance, including parasitic loads. Recent studies corroborate this finding. Mohammadi et al. (2025) reported that in vacuum ohmic systems, the energy consumed by the vacuum pump constituted 64.4\u0026ndash;89.8% of the total energy input, making the process significantly more energy-intensive than atmospheric operation. Similarly, Darvishi et al. (2021), concentrating kiwifruit juice, found that energy consumption in ohmic-vacuum mode was 0.68\u0026ndash;7.34 MJ/kg water higher than in ohmic-atmospheric mode, with the vacuum pump alone consuming 59\u0026ndash;81% of the total energy. Thus, the theoretical energy benefit of a lower boiling point under vacuum is negated by the substantial auxiliary energy required to maintain the vacuum [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. The processing time data, showing an 81% reduction from 39.55 min (50 kPa, 10 V/cm) to 7.70 min (100 kPa, 30 V/cm), strongly correlates with the SEC trends. Shorter processing times not only reduce energy input but also limit the thermal exposure of heat-sensitive compounds, conferring dual advantages of efficiency and quality preservation [47].\u003c/p\u003e \u003cp\u003eThe best conditions identified in this study (100 kPa, 30 V/cm) achieved a minimum SEC of 2.30 MJ/kg. This result demonstrates a remarkable efficiency compared to conventional thermal evaporation. Darvishi et al. (2020), for instance, reported that the conventional concentration of black mulberry juice consumed 17.50 MJ/kg water, which is 4.7-fold higher than the maximum SEC they recorded for ohmic heating and 8.0-fold higher than the optimal SEC achieved in the present work. This difference highlights the profound energy-saving potential of optimized ohmic heating technology for fruit juice concentration.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003e3.6. Optimization and Validation\u003c/h2\u003e \u003cp\u003eThe mathematical models presented in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, which exhibited high coefficients of determination (R\u0026sup2; = 0.9357\u0026ndash;0.9879), were employed as objective functions to predict system responses across the operational domain. The NSGA-II algorithm was configured with a population size of 100 chromosomes, operating over 150 generations with a crossover rate of 0.8 and a mutation rate of 0.2. Each chromosome encoded the two process parameters within their respective bounds, and fitness evaluation was performed by normalizing all five objective functions using min-max normalization to ensure equal weighting. The algorithm employed fast non-dominated sorting to classify solutions into Pareto fronts, with crowding distance calculations maintaining solution diversity throughout the evolutionary process. Binary tournament selection was utilized to choose parent chromosomes based on non-domination rank and crowding distance, while blend crossover and uniform mutation operators generated offspring populations.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eResponse models as a function of pressure and voltage gradient\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eResponse\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eModel*\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFSR\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eF-stat\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTime (min)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{T}\\text{i}\\text{m}\\text{e}=100.51-1.136\\text{P}-1.898\\nabla\\:\\text{V}+7.25\\times\\:{10}^{-3}{\\text{P}}^{2}+0.0531{\\nabla\\:\\text{V}}^{2}-0.0144\\text{P}\\times\\:\\nabla\\:\\text{V}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.9879\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.034\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e48.89\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSEC (MJ/kg water)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{S}\\text{E}\\text{C}=26.71-0.321\\text{P}-0.389\\nabla\\:\\text{V}+1.22\\times\\:{10}^{-3}{\\text{P}}^{2}+0.005{\\nabla\\:\\text{V}}^{2}+0.0007\\text{P}\\times\\:\\nabla\\:\\text{V}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.9499\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.121\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e11.38\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDPPH (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{A}\\text{C}=77.30+\\frac{3539}{\\text{P}}-\\frac{545.03}{\\nabla\\:\\text{V}}-\\frac{244800}{{\\text{P}}^{2}}-\\frac{2661}{{\\nabla\\:\\text{V}}^{2}}+\\frac{55244.5}{\\text{P}\\times\\:\\nabla\\:\\text{V}}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.9413\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3.484\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e9.621\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTPC (mg GAE/100 mL)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{T}\\text{P}\\text{C}=54.47-\\frac{4284.6}{\\text{P}}+\\frac{210.5}{\\nabla\\:\\text{V}}+\\frac{121904}{{\\text{P}}^{2}}-\\frac{3201.7}{{\\nabla\\:\\text{V}}^{2}}+\\frac{13019.6}{\\text{P}\\times\\:\\nabla\\:\\text{V}}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.9357\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.251\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e8.734\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTFC (mg CE/100 g)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{T}\\text{F}\\text{C}=\\frac{63.94-3.56\\text{P}+0.023{\\text{P}}^{2}+18.62\\text{l}\\text{n}\\text{P}}{1-0.040\\nabla\\:\\text{V}+0.0003{\\nabla\\:\\text{V}}^{2}+0.119\\text{l}\\text{n}\\nabla\\:\\text{V}}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.9862\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e10.391\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e23.900\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003eWhere, P is the pressure (kPa) and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\nabla\\:\\text{V}\\)\u003c/span\u003e\u003c/span\u003e is the voltage gradient (V/cm).\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe optimization convergence behavior demonstrated rapid improvement in the initial 80\u0026ndash;100 generations, after which the best fitness value stabilized, indicating successful identification of the optimal region. The final Pareto front revealed inherent trade-offs between bioactive compound retention and process efficiency. Analysis of the non-dominated solutions showed that conditions favoring maximum bioactive preservation (low voltage gradient and reduced pressure) inevitably resulted in extended processing times and elevated energy consumption, whereas conditions optimizing process efficiency (high voltage gradient and atmospheric pressure) led to moderate reductions in certain bioactive compounds, particularly TFC.\u003c/p\u003e \u003cp\u003eThe algorithm identified the optimal operating conditions that provided the best compromise among all five objectives. The optimal parameters were determined to be P\u0026thinsp;=\u0026thinsp;83.47 kPa and \u0026nabla;V\u0026thinsp;=\u0026thinsp;26.82 V/cm, yielding predicted responses of TPC\u0026thinsp;=\u0026thinsp;30.85 mg GAE/100 mL, DPPH\u0026thinsp;=\u0026thinsp;84.73%, TFC\u0026thinsp;=\u0026thinsp;78.14 mg CE/100 g, processing time\u0026thinsp;=\u0026thinsp;12.24 min, and SEC\u0026thinsp;=\u0026thinsp;2.87 MJ/kg water. This solution achieved a composite fitness value of 0.782, representing an excellent balance between product quality and operational efficiency.\u003c/p\u003e \u003cp\u003eTo validate the optimization results, triplicate experimental runs were conducted at the predicted optimal conditions (P\u0026thinsp;=\u0026thinsp;83.47 kPa, \u0026nabla;V\u0026thinsp;=\u0026thinsp;26.82 V/cm). The experimental values obtained were TPC\u0026thinsp;=\u0026thinsp;30.01\u0026thinsp;\u0026plusmn;\u0026thinsp;0.87 mg GAE/100 mL, DPPH\u0026thinsp;=\u0026thinsp;85.38\u0026thinsp;\u0026plusmn;\u0026thinsp;1.24%, TFC\u0026thinsp;=\u0026thinsp;75.68\u0026thinsp;\u0026plusmn;\u0026thinsp;3.45 mg CE/100 g, processing time\u0026thinsp;=\u0026thinsp;11.85\u0026thinsp;\u0026plusmn;\u0026thinsp;0.52 min, and SEC\u0026thinsp;=\u0026thinsp;2.94\u0026thinsp;\u0026plusmn;\u0026thinsp;0.15 MJ/kg water. Comparative analysis of the optimized conditions with individual optimal points for each response revealed the multi-objective nature of the problem. While 50 kPa and 10 V/cm provided maximum TPC (33.07 mg GAE/100 mL) and TFC (171.20 mg CE/100 g) retention, these conditions resulted in the longest processing time (39.55 min) and highest energy consumption (9.96 MJ/kg water), making them economically impractical for industrial-scale production. Conversely, 100 kPa and 30 V/cm achieved minimum processing time (7.70 min) and SEC (2.30 MJ/kg water) but with substantially reduced TFC (142.21 mg CE/100 g) compared to the gentlest conditions. The optimized solution at 83.47 kPa and 26.82 V/cm successfully balanced these competing objectives, retaining 91.3% of the maximum achievable TPC, 98.4% of peak antioxidant activity, while reducing processing time by 70.0% and energy consumption by 70.4% compared to the most quality-preserving conditions.\u003c/p\u003e \u003cp\u003eThe optimization results provide clear operational guidelines for industrial implementation based on production priorities. For premium, health-focused markets where bioactive compound retention is paramount, operating at 50 kPa and 10 V/cm maximizes nutritional quality despite elevated energy costs. For standard commercial production requiring a balance between quality and efficiency, the optimized conditions of approximately 75\u0026ndash;85 kPa with 25\u0026ndash;27 V/cm represent the ideal compromise, delivering excellent antioxidant capacity (\u0026gt;\u0026thinsp;84%), satisfactory phenolic retention (\u0026gt;\u0026thinsp;30 mg GAE/100 mL), rapid processing (\u0026lt;\u0026thinsp;13 min), and superior energy efficiency (\u0026lt;\u0026thinsp;3 MJ/kg water). For cost-driven industrial operations prioritizing throughput and minimal energy consumption, atmospheric pressure (100 kPa) with high voltage gradients (28\u0026ndash;30 V/cm) offers the most economically viable solution while maintaining acceptable bioactive compound levels. These scientifically validated recommendations enable manufacturers to optimize their ohmic-vacuum concentration processes according to specific market requirements and economic constraints.\u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThis study systematically evaluated conventional ohmic and hybrid ohmic-vacuum heating technologies for white mulberry syrup concentration, revealing critical trade-offs between bioactive compound retention and process efficiency. Increasing voltage gradient from 10 to 30 V/cm dramatically reduced processing time by 75.3% at atmospheric pressure, though vacuum conditions extended processing times by 81\u0026ndash;295% due to reduced electrical conductivity at lower temperatures. Total phenolic content degradation ranged from 28\u0026ndash;48%, with optimal retention (33.1 mg GAE/100 mL) at 50 kPa and 10 V/cm. Antioxidant capacity exhibited excellent preservation (62.13\u0026ndash;86.12%), peaking at 86.12% under intermediate conditions (75 kPa, 20 V/cm). Total flavonoid content showed remarkable variability (60.22\u0026ndash;171.20 mg CE/100 g), with 20 V/cm proving universally detrimental regardless of pressure. Counterintuitively, conventional ohmic heating demonstrated superior energy efficiency, consuming 2.5-3.7-fold less energy than hybrid ohmic-vacuum method due to substantial vacuum pump energy requirements. Multi-objective optimization using NSGA-II identified optimal conditions at 83.47 kPa and 26.82 V/cm, achieving an excellent compromise between bioactive retention and operational efficiency. These findings provide manufacturers with clear operational guidelines to select processing parameters based on product quality priorities versus cost-efficiency requirements, advancing sustainable food processing technologies.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eCompeting interests\u003c/h2\u003e \u003cp\u003eThe authors declare that they have no competing interests.\u003c/p\u003e \u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eThis research received no external funding.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eSoraya Kakaeie: Data curation; Methodology, Investigation.Hosain Darvishi: Supervision, Investigation, Writing \u0026ndash; original draft.Mahmoud Koushesh Saba: Methodology, Writing \u0026ndash; review \u0026amp; editing.Sirvan Mansouri: Investigation, Writing \u0026ndash; review \u0026amp; editing.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe datasets used and/or analysed during the current study available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAlkanan, Z. T., Altemimi, A. B., Al-Hilphy, A. R., Cacciola, F. \u0026amp; Ibrahim, S. A. Application and effects of ohmic-vacuum combination heating on the quality factors of tomato paste. Foods, 10(12), p.2920. (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAstrain-Redin, L., Ospina, S., Cebri\u0026aacute;n, G. \u0026amp; \u0026Aacute;lvarez-Lanzarote, I. Ohmic heating technology for food applications, from ohmic systems to moderate electric fields and pulsed electric fields. \u003cem\u003eFood Eng. Rev.\u003c/em\u003e \u003cb\u003e16\u003c/b\u003e (2), 225\u0026ndash;251 (2024).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAthira, V. A. et al. Advances in drying techniques for retention of antioxidants in agro produces. \u003cem\u003eCrit. Rev. Food Sci. Nutr.\u003c/em\u003e \u003cb\u003e63\u003c/b\u003e (31), 10849\u0026ndash;10865 (2023).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBerk, E. \u0026amp; G\u0026ouml;kmen, V. Evaporation in the fruit juice industry. In Evaporation Technology in Food Processing (105\u0026ndash;136). Woodhead Publishing. (2024).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBoateng, I. D. Recent processing of fruits and vegetables using emerging thermal and non-thermal technologies. A critical review of their potentialities and limitations on bioactives, structure, and drying performance. \u003cem\u003eCrit. Rev. Food Sci. Nutr.\u003c/em\u003e \u003cb\u003e64\u003c/b\u003e (13), 4240\u0026ndash;4274 (2024).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBozkir, H. \u0026amp; Tekg\u0026uuml;l, Y. Production of orange juice concentrate using conventional and microwave vacuum evaporation: thermal degradation kinetics of bioactive compounds and color values. \u003cem\u003eJ. Food Process. Preserv.\u003c/em\u003e \u003cb\u003e46\u003c/b\u003e (6), e15902 (2022).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCappato, L. P. et al. \u003cem\u003eOhmic heating in dairy processing: Relevant aspects for safety and quality\u003c/em\u003e Vol. 62, pp.104\u0026ndash;112 (Trends in Food Science \u0026amp; Technology, 2017).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCokgezme, O. F., Sabanci, S., Cevik, M., Yildiz, H. \u0026amp; Icier, F. Performance analyses for evaporation of pomegranate juice in ohmic heating assisted vacuum system. \u003cem\u003eJ. Food Eng.\u003c/em\u003e \u003cb\u003e207\u003c/b\u003e, 1\u0026ndash;9 (2017).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCroguennec, T. Non-enzymatic browning. Handbook of food science and technology 1: food alteration and food quality, pp.133\u0026ndash;157. (2016).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDarvishi, H., Behroozi-Khazaei, N., Saba, K., Alimohammadi, M., Nourbakhsh, H. \u0026amp; Z., \u0026amp; The influence of Ohmic-vacuum heating on phenol, ascorbic acid and engineering factors of kiwifruit juice concentration process. \u003cem\u003eInt. J. Food Sci. Technol.\u003c/em\u003e \u003cb\u003e56\u003c/b\u003e (9), 4789\u0026ndash;4798 (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDarvishi, H., Mohammadi, P., Fadavi, A., Koushesh Saba, M. \u0026amp; Behroozi-Khazaei, N. Quality preservation of orange concentrate by using hybrid ohmic\u0026ndash;vacuum heating. \u003cem\u003eFood Chem.\u003c/em\u003e \u003cb\u003e289\u003c/b\u003e, 292\u0026ndash;298 (2019).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDarvishi, H., Salami, P., Fadavi, A. \u0026amp; Saba, M. K. Processing kinetics, quality and thermodynamic evaluation of mulberry juice concentration process using Ohmic heating. \u003cem\u003eFood Bioprod. Process.\u003c/em\u003e \u003cb\u003e123\u003c/b\u003e, 102\u0026ndash;110 (2020).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFadavi, A. \u0026amp; Salari, S. Ohmic heating of lemon and grapefruit juices under vacuum pressure\u0026mdash;comparison of electrical conductivity and heating rate. \u003cem\u003eJ. Food Sci.\u003c/em\u003e \u003cb\u003e84\u003c/b\u003e (10), 2868\u0026ndash;2875 (2019).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFadavi, A., Yousefi, S., Darvishi, H. \u0026amp; Mirsaeedghazi, H. \u003cem\u003eComparative study of ohmic vacuum, ohmic, and conventional-vacuum heating methods on the quality of tomato concentrate\u003c/em\u003e Vol. 47, pp.225\u0026ndash;230 (Innovative Food Science \u0026amp; Emerging Technologies, 2018).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGavahian, M. \u0026amp; Chu, R. Ohmic heating extraction at different times, temperatures, voltages, and frequencies: a new energy-saving technique for pineapple core valorization. Foods, 11(14), p.2015. (2022).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGundogdu, M., Canan, I., Gecer, M. K., Kan, T. \u0026amp; Ercisli, S. Phenolic compounds, bioactive content and antioxidant capacity of the fruits of mulberry (Morus spp.) germplasm in Turkey. \u003cem\u003eFolia Horticulturae\u003c/em\u003e. \u003cb\u003e29\u003c/b\u003e (2), 251\u0026ndash;262 (2017).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHardinasinta, G., Mursalim, M., Muhidong, J. \u0026amp; Salengke, S. Degradation kinetics of anthocyanin, flavonoid, and total phenol in bignay (Antidesma bunius) fruit juice during ohmic heating. \u003cem\u003eFood Sci. Technol.\u003c/em\u003e \u003cb\u003e42\u003c/b\u003e, e64020 (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHosainpour, A., Kheiralipour, K., Nadimi, M. \u0026amp; Paliwal, J. Quality assessment of dried white mulberry (Morus alba L.) using machine vision. Horticulturae, 8(11), p.1011. (2022).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHwang, J. H., Jung, A. H. \u0026amp; Park, S. H. Efficacy of Ohmic Vacuum Concentration for orange juice concentrates and their physicochemical properties under different voltage gradients. \u003cem\u003eLWT - Food Sci. Technol.\u003c/em\u003e \u003cb\u003e154\u003c/b\u003e, 112750 (2022).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eIoannou, I., Chekir, L. \u0026amp; Ghoul, M. Effect of heat treatment and light exposure on the antioxidant activity of flavonoids. Processes, 8(9), p.1078. (2020).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eIsmail, M., \u0026Ouml;zbek, H. N. \u0026amp; G\u0026ouml;ğ\u0026uuml;ş, F. Combined vacuum osmotic dehydration by pomegranate juice concentrate and hot-air assisted radiofrequency drying to produce fortified orange slices. Scientific Reports, 15(1), p.36001. (2025).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJaeger, H. et al. \u003cem\u003eOpinion on the use of ohmic heating for the treatment of foods\u003c/em\u003e Vol. 55, pp.84\u0026ndash;97 (Trends in Food Science \u0026amp; Technology, 2016).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKarakavuk, E., Goksu, A. \u0026amp; Sabanci, S. \u003cem\u003eInvestigation of electrical conductivity and bioactive quality during ohmic evaporation process of Apple juice\u003c/em\u003e (Journal of Food Processing and Preservation, 2022).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKumar, A., Kumar, M., Mahboob, M. R. \u0026amp; Srivastava, B. Influence of\u0026deg; Brix/Acid, and flow rate of pineapple juice and electric field strength on the performance of continuous ohmic heating system. \u003cem\u003eJ. Food Sci. Technol.\u003c/em\u003e \u003cb\u003e61\u003c/b\u003e (6), 1188\u0026ndash;1200 (2024).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu, Y. et al. Degradation of biochemical fractions in different temperature of food waste bioevaporation and their contribution to biogenerated heat. Journal of Cleaner Production, 245, p.118944. (2020).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNofiyanti, S. H., Fajarini, L. D. R., Putra, I. G. A. M. \u0026amp; Arista, Y. L. V. Process Intensification of Polyphenol and Flavonoid Extraction from Ant Nest (Myrmecodia pendans) via Ohmic Heating: Investigating Joule Heating and Electric Field-Time Interactions Using a Response Surface Methodology. \u003cem\u003eTrends Sci.\u003c/em\u003e \u003cb\u003e22\u003c/b\u003e (11), 10471\u0026ndash;10471 (2025).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNorouzi, S., Fadavi, A. \u0026amp; Darvishi, H. The ohmic and conventional heating methods in concentration of sour cherry juice: Quality and engineering factors. Journal of Food Engineering, 291, p.110242. (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSabanci, S. \u0026amp; Icier, F. Applicability of ohmic heating assisted vacuum evaporation for concentration of sour cherry juice. \u003cem\u003eJ. Food Eng.\u003c/em\u003e \u003cb\u003e212\u003c/b\u003e, 262\u0026ndash;270 (2017).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSabanci, S., Cevik, M., Cokgezme, O. F., Yildiz, H. \u0026amp; Icier, F. Quality characteristics of pomegranate juice concentrates produced by ohmic heating assisted vacuum evaporation. \u003cem\u003eJ. Sci. Food. Agric.\u003c/em\u003e \u003cb\u003e99\u003c/b\u003e (5), 2589\u0026ndash;2595 (2019).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSain, M., Minz, P. S., John, H. \u0026amp; Singh, A. Effect of ohmic heating on food products: An in-depth review approach associated with quality attributes. \u003cem\u003eJ. Food Process. Preserv.\u003c/em\u003e \u003cb\u003e2024\u003c/b\u003e (1), 2025937 (2024).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSalari, S. \u0026amp; Jafari, S. M. The influence of ohmic heating on degradation of food bioactive ingredients. \u003cem\u003eFood Eng. Rev.\u003c/em\u003e \u003cb\u003e12\u003c/b\u003e (2), 191\u0026ndash;208 (2020).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eS\u0026aacute;nchez-Moreno, C., Larrauri, J. A. \u0026amp; Saura-Calixto, F. Free radical scavenging capacity and inhibition of lipid oxidation of wines, grape juices and related polyphenolic constituents. \u003cem\u003eFood Res. Int.\u003c/em\u003e \u003cb\u003e32\u003c/b\u003e (6), 407\u0026ndash;412 (1999).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSastry, S. K., Heskitt, B. F., Sarang, S. S., Somavat, R. \u0026amp; Ayotte, K. Why ohmic heating? Advantages, applications, technology, and limitations. In Ohmic heating in food processing (Vol. 7, 7\u0026ndash;16). Boca Raton: CRC. (2014).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSingleton, V. L., Orthofer, R. \u0026amp; Lamuela-Raventos, R. M. Analysis of total phenols and other oxidation substrates and antioxidants by means of Folin\u0026ndash;Ciocalteu, s reagent. \u003cem\u003eMethods Enzymol.\u003c/em\u003e \u003cb\u003e299\u003c/b\u003e, 152\u0026ndash;178 (1999).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSofizadeh, T., Khodaei, J., Darvishi, H., Behroozi-Khazaei, N. \u0026amp; Koushesh Saba, M. Process parameters of microwave heating-assisted vacuum evaporation of tomato juice: quality, energy consumption, exergy performance, and kinetic processing. \u003cem\u003eJ. Microw. Power Electromagn. Energy.\u003c/em\u003e \u003cb\u003e57\u003c/b\u003e (3), 203\u0026ndash;218 (2023).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVahedi-Torshizi, M., Azadbakht, M. \u0026amp; Kashaninejad, M. Evaluation of the Effect of the Ohmic Process on the Physicochemical Properties of Sour Orange Juice Using Principal Component Analysis (PCA). \u003cem\u003eBiosystems Eng. Renew. Energies\u003c/em\u003e. \u003cb\u003e1\u003c/b\u003e (2), 106\u0026ndash;114 (2025).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWani, M. Y. et al. The phenolic components extracted from mulberry fruits as bioactive compounds against cancer: A review. \u003cem\u003ePhytother. Res.\u003c/em\u003e \u003cb\u003e37\u003c/b\u003e (3), 1136\u0026ndash;1152 (2023).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWu, B. et al. Effect of ultrasound-assisted vacuum far-infrared on the drying characteristics and qualities attributes of Cistanche slices. Agriculture, 14(4), p.557. (2024).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWu, W. et al. Effects of high pressure and thermal processing on quality properties and volatile compounds of pineapple fruit juice. Food Control, 130, p.108293. (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZandi, N., Khodaei, J., Darvishi, H., Behroozi-Khazaei, N. \u0026amp; Koushesh Saba, M. Black Grape Juice Concentration via Ohmic-Vacuum Hybrid Heating: Quality Parameters, Energy Consumption and Exergy Efficiency. \u003cem\u003eInnovative Food Technol.\u003c/em\u003e \u003cb\u003e12\u003c/b\u003e (4), 321\u0026ndash;337 (2025).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhishen, J., Mengcheng, T. \u0026amp; Jianming, W. The determination of flavonoid contents in mulberry and their scavenging effects on superoxide radicals. \u003cem\u003eFood Chem.\u003c/em\u003e \u003cb\u003e64\u003c/b\u003e (4), 555\u0026ndash;559 (1999).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZia, H., Slatnar, A., Košmerl, T. \u0026amp; Korošec, M. A review study on the effects of thermal and non-thermal processing techniques on the sensory properties of fruit juices and beverages. \u003cem\u003eFront. Food Sci. Technol.\u003c/em\u003e \u003cb\u003e4\u003c/b\u003e, 1405384 (2024).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Ohmic heating, Vacuum concentration, White mulberry syrup, Bioactive compounds, Energy consumption, Multi-objective optimization","lastPublishedDoi":"10.21203/rs.3.rs-8096105/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8096105/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study systematically compared conventional ohmic heating and hybrid ohmic-vacuum heating technologies for white mulberry syrup concentration, evaluating the interactive effects of voltage gradient (10\u0026ndash;30 V/cm) and pressure (50\u0026ndash;100 kPa) on bioactive compound retention, energy efficiency, and process optimization. Multi-objective optimization was performed using Non-dominated Sorting Genetic Algorithm II (NSGA-II) to simultaneously maximize bioactive compounds while minimizing processing time and energy consumption. Results demonstrated that increasing voltage gradient from 10 to 30 V/cm reduced processing time by 75.3% at atmospheric pressure, though ohmic-vacuum conditions exhibited 81\u0026ndash;295% longer processing times due to reduced electrical conductivity at lower temperatures. Total phenolic content decreased by 28\u0026ndash;48% across all treatments, with best retention (33.1 mg GAE/100 mL) achieved at 50 kPa and 10 V/cm. Antioxidant capacity showed excellent preservation (62.13\u0026ndash;86.12%), peaking at 86.12% under intermediate conditions (75 kPa, 20 V/cm). Total flavonoid content exhibited dramatic variability (60.22\u0026ndash;171.20 mg CE/100 g), with maximum retention at 50 kPa and 10 V/cm, while 20 V/cm proved universally detrimental regardless of pressure. Counterintuitively, conventional ohmic heating demonstrated superior energy efficiency, with specific energy consumption 2.5-3.7-fold lower than hybrid ohmic-vacuum method. NSGA-II optimization identified the best conditions at 83.47 kPa and 26.82 V/cm, which yielded the following experimental responses: 30.85 mg GAE/100 mL for total phenol content, 84.73% for antioxidant capacity, 78.14 mg CE/100 g for total flavonoid content, 12.24 min for processing time, and 2.87 MJ/kg water for energy consumption.\u003c/p\u003e","manuscriptTitle":"Comparative Study of Conventional Ohmic and Hybrid Ohmic-Vacuum Heating for White Mulberry Syrup Concentration: Bioactive Compound Retention, Energy Consumption, and Multi-objective Optimization","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-17 09:24:11","doi":"10.21203/rs.3.rs-8096105/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-03-10T09:43:52+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-03-07T15:15:29+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-03-03T16:35:54+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"194812002035847913022988037674119428666","date":"2026-02-18T23:39:45+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-02-18T21:32:31+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"179955273606529858339407311889081248749","date":"2026-02-18T19:44:46+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-02-13T12:36:20+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"328139747744684719979689507901330710786","date":"2026-02-13T08:11:25+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"321900129599760934562425073139220377997","date":"2026-02-12T15:13:25+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"98445492952221166963171405723747600378","date":"2026-02-12T13:39:30+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-02-12T04:43:04+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-11-24T12:54:00+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-11-17T19:05:19+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2025-11-17T19:02:06+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"70bc4721-e01e-4910-a1cb-1aed379d7d46","owner":[],"postedDate":"February 17th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":62920660,"name":"Physical sciences/Chemistry"},{"id":62920661,"name":"Physical sciences/Engineering"},{"id":62920662,"name":"Biological sciences/Plant sciences"}],"tags":[],"updatedAt":"2026-05-06T14:23:24+00:00","versionOfRecord":[],"versionCreatedAt":"2026-02-17 09:24:11","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8096105","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8096105","identity":"rs-8096105","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}