Phenolic Profile Characterization of Extra Virgin Olive Oils from the Omani Market Using a Salt-Assisted Extraction and LC-MS/MS Approach

Phenolic Profile Characterization of Extra Virgin Olive Oils from the Omani Market Using a Salt-Assisted Extraction and LC-MS/MS Approach | 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 Research Article Phenolic Profile Characterization of Extra Virgin Olive Oils from the Omani Market Using a Salt-Assisted Extraction and LC-MS/MS Approach Azza A.H. Al Shamli¹, Maryam Mousavizadegan¹, Haider A. J. Al Lawati¹ This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9117332/v1 This work is licensed under a CC BY 4.0 License Status: Under Revision Version 1 posted 10 You are reading this latest preprint version Abstract This study investigates the phenolic composition of extra virgin olive oil (EVOO) from the Omani market and optimizes the phenolic extraction process. The addition of 10% (w/v) sodium chloride to the extraction solvent increased phenolic recovery by 20–30%. Feature importance analysis identified solvent polarity, influenced by solvent type, salt concentration, and volume, as the key factor driving extraction efficiency. A validated liquid chromatography–tandem mass spectrometry (LC–MS/MS) method quantified ten phenolic compounds in six commercial EVOO samples. Acid values ranged from 0.01% to 0.11%, and peroxide values were below 12 meq O₂ kg⁻¹, confirming compliance with EVOO quality standards. Total phenolic content ranged from 116 to 250 mg kg⁻¹. Two locally produced Omani oils exhibited phenolic profiles comparable to high-quality Mediterranean EVOOs. Elevated hydroxytyrosol levels indicate phenolic transformation during storage. This study provides baseline data supporting quality control and nutritional evaluation of EVOOs in the Omani market. Extra virgin olive oil Phenolic compounds LC–MS/MS Salt-assisted extraction Hydroxytyrosol Omani market Figures Figure 1 Figure 2 1. Introduction Olive oil, obtained through the mechanical extraction of the fruit of Olea europaea L. , member of the Oleaceae family, has become an inseparable component in most culinary routines. It mainly consists of a glycerol fraction, comprising about 90–99%, alongside a non-glycerol fraction that ranges from 0.4% to 5%. Oleic acid represents roughly 70–80% of the fatty acids present in olive oil (Tripoli et al., 2005 ). The beneficial properties of olive oil are largely attributed to the antioxidant effects of its components (Tripoli et al., 2005 ). Extra virgin olive oil (EVOO) primarily contains volatile compounds, aliphatic and triterpenic alcohols, sterols, and various antioxidants. Among these, phenolic compounds stand out as a particularly abundant family of antioxidants in EVOO. These compounds fall into several classes, with the most prominent being simple phenols, phenolic acids, phenolic alcohols, hydroxyisochromans, secoiridoids, lignans, and flavonoids (Tripoli et al., 2005 ). Extra virgin olive oil production has only recently begun in Oman, mainly around Jabal Al Akhdar (JA) in the northern part of the country, within Al Dakhiliyah Governorate. JA stretches about 80 km long and 32 km wide, sitting at an elevation of 2000 meters above sea level (Al-Busaidi, 2012 ). The region is characterized by a Mediterranean climate, with average air temperatures ranging from 7.4 to 23.0°C and ground temperatures between 7.9 and 23.7°C (Al-Busaidi, 2012 ). In 2012, approximately 15,000 olive trees were cultivated in JA (Al-Busaidi, 2012 ). According to data from Oman’s Ministry of Agriculture and Fisheries, a total of sixty tons of olives were harvested during the period from August to December 2019. This harvest yielded roughly 8,000 liters of EVOO, valued at OMR 160,000, based on a price of OMR 20 per liter (Al-Hashmi et al., 2025 ). It is well known that the chemical composition of EVOO is highly sensitive to storage conditions, especially heat and sunlight (Medina et al., 2022 ). Given the harsh climate of Oman, with temperatures exceeding 50°C during summer and intense sunshine, quality control and phenolic content assessment of olive oil in the Omani market is critical. Different liquid–liquid extraction methods have been reported using a variety of solvents to isolate phenolic compounds from olive oil (Bonoli et al., 2004 ; Hrncirik & Fritsche, 2004 ; Arrasco-Pancorbo et al., 2004 ; García-Villalba et al., 2010; Cioffi et al., 2010 ; Luaces et al., 2021; Eroglu & Girgin, 2021 .; Behbahan & Al Lawati, 2025 ). Common solvents include methanol–water mixtures at ratios such as 60:40 or 80:20 (v/v), which effectively extract the hydroalcoholic phase from oil samples (Bonoli et al., 2004 ; Hrncirik & Fritsche, 2004 ; Arrasco-Pancorbo et al., 2004 ). Hexane or n-hexane is often employed as the non-polar solvent to separate oil fractions and aid in recovering phenolic compounds (Bonoli et al., 2004 ; Hrncirik & Fritsche, 2004 ; Arrasco-Pancorbo et al., 2004 ). Acetonitrile is also used to dissolve and wash extracts, improving selectivity during extraction (García-Villalba et al., 2010). Dimethyl sulfoxide has been suggested as an alternative solvent for extracting phenolics from olive fruit and macerates, demonstrating effectiveness in isolating diverse phenolic derivatives (Luaces et al., 2021). Additionally, blends of organic solvents such as ethanol–chloroform–acetone–water mixtures are used for thorough extraction from both oil and solid olive matrices (Criado-Navarro et al., 2022 ). These solvent systems are chosen to maximize phenolic recovery while ensuring compatibility with subsequent chromatographic and spectrometric analyses (Behbahan & Al Lawati, 2025 ). In this study, phenolic extraction optimization is carried out and the addition of sodium chloride to the extraction solvent was tested to assess its impact on phenolic extraction. We then used feature importance via machine learning techniques, specifically Random Forest's mean decreases impurity (MDI) and SHAP (SHapley Additive exPlanations) to better gain insight on how various parameters can impact the efficiency of phenolic extraction. The optimized extraction technique was then applied to develop an LC/MS/MS method for detecting 10 phenolic compounds in olive oil, including hydroxytyrosol, tyrosol, luteolin, oleuropein, apigenin, diosmetin, pinoresinol, p-coumaric acid, oleacein, and oleocanthal. Finally, the method was used to analyze six commercial olive oil samples from the local market, two of which were produced locally in the Sultanate of Oman. This study represents the first report evaluating the phenolic content of olive oil from the Omani market and comparing it with other olive oils documented in the literature. 2. Materials and Methods 2.1. Samples EVOO samples were obtained from local markets located in Muscat, Oman. A batch of 0.5 L of six brands EVOO were collected. Brand A (Production date, 05/2025), B (production date, 04/2025), C (production date, 02/2025). These three brands were Spanish originated olive oil. Brand D (production date 03/2024) was Tunisian EVOO and Brands E (production date, 05/2025) and F (October 2024) were locally produced. The samples were transported immediately to the laboratory and analyzed directly. The remaining was stored in amber glass bottles at 20°C for further analyses if needed. 2.2. Chemicals Analytical standards of hydroxytyrosol, tyrosol, p-coumaric acid, ferulic acid, luteolin, apigenin, pinoresinol, diosmetin, oleacein, oleocanthal, oleuropein, and caffeic acid were purchased from PhytoLab (Germany) and Sigma-Aldrich (UK). Caffeic acid—an analyte not naturally present in Olea europaea—was selected and used as an internal standard (IS). Individual stock solutions were prepared by dissolving 10 mg of each pure standard in 10 mL of methanol to obtain concentrations of 1000 mg/L. A composite standard solution (100 mg/L for each analyte) was prepared by mixing appropriate aliquots of the individual stock solutions and diluting with methanol. All standard solutions were stored at 5°C and equilibrated to room temperature prior to use. Working individual and mixed standard solutions were prepared by further dilution with methanol or water, stored at 4°C, and freshly prepared on a weekly basis. All organic solvents, reagents, and salts were of analytical or HPLC grade and procured from Sigma-Aldrich (UK). Ultrapure water was produced using a Milli-Q SP Water System (Millipore, USA). Folin–Ciocalteu reagent, sodium carbonate, and gallic acid were purchased from VWR International (France). A vortex mixer (Whirlimixer, England) and a centrifuge (Labdex, UK) were used for sample preparation throughout the study. 2.3. Extraction of phenolic compounds from EVOO and feature importance A 3.0 g aliquot of EVOO was weighed into a centrifuge tube, followed by addition of 3.0 mL n-hexane and 1.5 mL of methanol: water: NaCl (80:20:10 v/v). Subsequently, 10 µL of caffeic acid (IS) was added. The mixture was vortexed for 5 min and centrifuged for 10 min at 1000 rpm. The hydroalcoholic phase was collected, and the hexane layer was re-extracted twice using 1.5 mL methanol: water (80:20, v/v). The combined extracts were filtered through 0.22 µm nylon filters before HPLC/LC-MS/MS analysis. Each sample was extracted in triplicate (n = 3). To evaluate the impact of the various experimental parameters on the efficiency of the phenolic extraction, two complementary machine learning (ML) approaches were implemented for feature importance analysis including Mean Decrease in Impurity (MDI) and SHapley Additive exPlanations (SHAP) methods. For this, each experiment was described using polarity index of the solvent, dipole moment, ratio of solvent, percentage of NaCl and overall system polarity. MDI is a method used in tandem with tree-based learners and it measures how each variable reduces prediction error across decision trees splits. SHAP quantifies the contribution of each feature to individual predictions using game-theoretic Shapley values for model-consistent interpretability. All ML calculations were carried out on Python 3.14 using the scikit-learn package. First, a Random Forest regressor with 100 trees and a fixed random seed was developed. Using the algorithms built-in impurity-based feature importance method (MDI), the contribution of various parameters was evaluated and the resulting importance scores were extracted. SHAP analysis was also performed for further assessment of feature importance. After the Random Forest regression model was developed, SHAP values were computed using the TreeExplainer method to attain game-theoretic estimates of the contribution of each feature on total extracted phenolic compound values. Mean absolute SHAP values were thus extracted and ranked. The Python scripts used for Random Forest modeling and SHAP analysis are available from the corresponding author upon reasonable request. 2.4. Preparation of standards Calibration curves were constructed using standard solutions of hydroxytyrosol, tyrosol, p-coumaric acid, ferulic acid, luteolin, apigenin, pinoresinol, diosmetin, oleacein, oleocanthal, oleuropein, and caffeic acid. Stock standard solutions (1000 mg/L) were prepared by dissolving 10 mg of each compound in 100 mL water or methanol. Calibration curves were generated by plotting peak area versus concentration. 2.5. LC-MS/MS analysis An LC-MS/MS system (Shimadzu, Japan) equipped with an LC-2040 pump, LC-2040 autosampler, LC-2040 oven and an ESI source was used. The ESI source parameters were set as follows: capillary voltage, − 3500 V (+ 3500 V); sheath gas flow rate, 11 L min⁻¹; sheath gas temperature, 350°C; nebulizer pressure, 35 psi; drying gas temperature, 150°C; drying gas flow rate, 15 L min⁻¹; and fragmentor voltage, 360 V. Nitrogen was used as the nebulizer, drying, and collision gas. Mass spectra were acquired over an m/z range of 100–1100. Compound identity was confirmed using retention times, accurate mass, and fragmentation patterns, and through co-injection with commercial standards. Separation was achieved using a reversed-phase C18 Eclipse Plus column (3.5 µm, 2.1 mm × 100 mm). A gradient elution program (Table S1 ) was employed using a binary mobile phase consisting of (A) methanol containing 0.1% trifluoroacetic acid (TFA) and (B) water containing 0.1% TFA. The flow rate was maintained at 0.2 mL min⁻¹, with an injection volume of 10 µL. The column temperature was set at 50°C. LabSolution software (version 5.82) was used for data acquisition, post-run analysis and peak characterization. 2.6. Recovery Study Recovery of phenolic compounds was evaluated by spiking EVOO/hexane solutions with standards at levels approximately 3–5 times the natural concentration. 2.7. Determination of total phenolic content Total phenolic content was determined using the Folin–Ciocalteu spectrophotometric method (Shimadzu UV-VIS 1900, Kyoto, Japan). A 0.1 mL aliquot of the extract was mixed with 2.5 mL of 1:10 diluted Folin–Ciocalteu reagent and allowed to stand for 8 min. Subsequently, 2.0 mL of 7.5% Na₂CO₃ was added, and the mixture was incubated for 30 min in the dark. Absorbance was measured at 760 nm. Quantification was performed using a gallic acid calibration curve (50–500 mg kg⁻¹; r² = 0.996). Results were expressed as mg gallic acid equivalents (GAE) per kg of oil. Each extract was analyzed in triplicate. 3. Results and Discussion 3.1. Sample preparation and quality evaluation Given the increasing market of olive oil production in Oman, and considering Oman’s harsh climate especially in summer where temperature can reach 50°C. Such high temperatures may affect negatively the quality of EVOO during storage, we have attempted to evaluate the quality of olive oil in Omani market in terms of phenolic content richness compared to other markets. The Omani market, like other international markets, offers a range of commercial olive oils which were used in comparison with two locally produced Omani EVOO samples. The two samples analyzed in this study include one from a single cultivar (Picual) (Brand F) and the other a blend of multiple cultivars (Brand E). The analysis of the olive oil samples based on acid value and peroxide value provides insightful information regarding their quality and oxidative state. Acid value (AV) is a critical parameter reflecting the level of free fatty acids, which increase as a result of hydrolytic degradation. The values observed across all six samples ranged from 0.01% to 0.11%, significantly below the internationally recognized threshold of 0.8% for EVOO (Table 1 ). These low acid values indicate that the oils have undergone minimal hydrolysis, suggesting good handling practices and preservation of oil integrity from production to analysis. Peroxide value (PV) serves as an indicator of primary oxidation products, revealing the extent to which the oils have undergone oxidative deterioration. The peroxide values measured in Samples A, B, and C were 9.90, 11.93, and 9.94 meq O₂ kg⁻¹ respectively (Table 1 ). While all these values fall within acceptable limits for fresh olive oil, the relatively elevated PV in Sample B suggests a higher degree of oxidation compared to Samples A and C. This may be attributed to factors such as prolonged exposure to oxygen, light or suboptimal storage conditions. On the other hand, Samples D, E and F exhibited undetectable peroxide values, indicating exceptional freshness and minimal exposure to oxidative stress. The combined interpretation of acid and peroxide values suggests that all samples meet the quality standards for EVOO, with samples 4, 5 and 6 demonstrating superior preservation of freshness and oxidative stability. The variation in peroxide values among the samples highlights the sensitivity of olive oil to environmental factors influencing lipid oxidation. This underscores the importance of proper storage and handling to maintain oil quality over time. Table 1 Acid value and peroxide value of olive oil samples Sample Acid value (% as oleic acid) Peroxide value (meq O₂ kg⁻¹) A 0.09 9.90 B 0.06 11.93 C 0.11 9.94 D 0.03 ND E 0.01 ND F 0.01 ND ND, not detected. 3.2. Optimization of phenolic extraction Various extraction techniques have been reported for isolating phenolic compounds from olive oil, using different solvents or solvent mixtures such as methanol, ethanol, or acetonitrile combined with water at varied concentrations (Behbahan & Al Lawati, 2025 ). In this study, the addition of sodium chloride (NaCl) at concentrations between 10 and 20% (w/v) to the extraction solvent resulted in a 20 to 30% improvement in extraction efficiency. Initially, a solvent containing 60% methanol was employed to extract phenolic compounds from olive oil. The phenolic content was quantified using the Folin-Ciocalteu (FC) method, yielding an average concentration of 400 ± 13 ppm (relative standard deviation, RSD, 3%) across three replicates. Upon the addition of 20% (w/v) NaCl to this solvent system, the phenolic content significantly increased to 517 ± 44 ppm (RSD 2%). Further testing of varying methanol and NaCl concentrations revealed that an 80% methanol solvent combined with 10% NaCl achieved the highest extraction efficiency, with a low RSD of 0.1% (520 ± 3 ppm). A similar trend was observed when using acetonitrile; the addition of 20% (w/v) NaCl to 80% acetonitrile improved extraction efficiency by approximately 20%. Conversely, using ethanol as the organic solvent reduced extraction efficiency to 392 ± 18 ppm (RSD 1.1%). Increasing the water content to 40% ethanol with 20% (w/v) NaCl did not enhance extraction efficiency, resulting in 292 ± 13 ppm (RSD 1.2%). To assess the influence of multiple factors—including the type and concentration of the organic solvent, NaCl concentration, and overall solution polarity—machine learning-based feature importance analyses were conducted using Random Forest mean decrease impurity (MDI) and SHapley Additive exPlanations (SHAP) methods. Both analyses identified the overall polarity of the extraction system as the most critical variable, influenced directly by solvent type, NaCl concentration, and solvent volume (Figure S1 ). Additionally, both the organic solvent amount and NaCl concentration ranked as significant contributors. These results indicate that the total polarity of the system is pivotal for enhancing phenolic compound extraction. Although NaCl does not directly increase the polarity of water molecules, it induces strong ion-dipole interactions that can alter the behavior of the solution, effectively increasing its overall polarity. This phenomenon also explains the reduced extraction efficiency observed with ethanol, which exhibits lower polarity than methanol and acetonitrile. The Python scripts used for Random Forest modeling and SHAP analysis are available from the corresponding author upon reasonable request. 3.3. LC–MS/MS method development and validation A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for phenolic compound analysis. While p-coumaric acid is commonly used as an internal standard, its presence in the olive oil samples here necessitated the use of caffeic acid as the internal standard instead. Prior to quantification, the identification of the ten phenolic compounds was confirmed via LC-MS/MS, based on retention times, molecular masses, and daughter ion profiles. The data obtained from the MS/MS detector are provided in Table 2 and Figure S2 shows the mass spectra of daughter ions (m/z) of the 10 components. Table 2 Retention time and MS/MS parameters of phenolic compounds Compound Precursor ion (m/z) Retention time (min) Daughter ions (m/z) Caffeic acid (IS) 179 2.0 90, 115, 135 p-Coumaric acid 163 2.5 90, 93, 117, 119 Hydroxytyrosol 153 5.7 69, 108, 109, 115, 123 Tyrosol 137 7.1 106, 119 Oleacein 319 11.0 69 Pinoresinol 357 12.2 136, 151, 311, 342 Oleocanthal 303 12.3 59 Luteolin 285 13.2 107, 133, 135, 151 Apigenin 269 14.3 107, 117, 149 Diosmetin 299 14.5 135, 284 Oleuropein 539 21.9 307, 377 The performance of the analytical method was validated using standard solutions of the phenolic compounds, evaluating precision, linearity, accuracy, limit of detection (LOD), and limit of quantitation (LOQ). Precision was maintained through triplicate injections. Calibration curves constructed with 8–10 concentration points ranging from 0.01 to 10 mg kg⁻¹ displayed strong linearity for all compounds, confirming method reliability and precision. Accuracy of the extraction was assessed by determining recovery rates through spiking EVOO/hexane solutions with phenolic standards at levels approximately three to five times the natural concentrations. The recovery was calculated as: Recovery (%) = (( C _found − C _original) / C _spiked) × 100 (1) Where C is the concentration. All recovery measurements were performed in triplicate. The results indicated that the average percentage recovery values for the ten phenolic compounds ranged from 75% for diosmetin to 138% for oleacein, demonstrating the reliability and consistency of the extraction method employed. The limit of detection (LOD) is a critical analytical parameter, defined as the lowest analyte concentration that can be distinguished from background noise, typically set at three times the noise level. Meanwhile, the limit of quantification (LOQ) refers to the lowest analyte concentration that can be measured with acceptable accuracy and precision, established by analyzing at least ten sample blanks and applying a factor of ten to ensure reliable quantification (González & Herrador, 2007 ). The lowest LOD values observed were 0.002 mg L⁻¹ for tyrosol, oleacein, luteolin, apigenin, and diosmetin, while the highest was 0.02 mg L⁻¹ for pinoresinol. LOQ values ranged from 0.006 to 0.060 mg L⁻¹. A summary of all validation parameters is provided in Table 2 . 3.4. Separation and quantification of phenolic compounds by LC-MS/MS This study focused on ten primary phenolic compounds. Table 2 lists their retention times. The elution order generally reflects differences in polarity and molecular structure; less polar compounds experience longer retention times, enabling separation based on these differences (Abdu Hussen, 2022 ). Phenolic acids, which exhibit high polarity due to partial charges at neutral pH, elute first. Hydroxytyrosol, a relatively hydrophilic phenolic compound with a single hydroxyl group, follows the phenolic acids in elution order. Tyrosol, structurally similar but slightly more hydrophobic, elutes subsequent to hydroxytyrosol. More hydrophobic compounds such as oleacein, oleocanthal, pinoresinol, luteolin, apigenin, and diosmetin interact more strongly with the stationary phase, resulting in later elution times. Oleuropein, the largest molecule with the greatest number of interaction sites, elutes last at approximately 21.9 minutes. Figure 1 presents the quantitative analysis of the ten targeted phenolic compounds across six olive oil samples. Hydroxytyrosol, oleocanthal, and luteolin were consistently the most abundant compounds in all samples. Among the ten compounds analyzed, oleocanthal, oleacein, hydroxytyrosol, and tyrosol are recognized for their therapeutic properties (Tasioula-Margari & Tsabolatidou, 2015 ). Hydroxytyrosol and tyrosol exhibit cardioprotective effects, while oleocanthal and oleacein possess potent anti-inflammatory activities. Literature reports indicate that phenolic compound concentrations shift during EVOO storage: oleocanthal and oleacein decrease, whereas simpler phenols such as tyrosol and hydroxytyrosol increase. This increase is attributed to the breakdown of more complex secoiridoid derivatives over time (Alessandri et al., 2014 ; Luaces et al., 2021d; Palla et al., 2018 ; Sicari, 2017 ). One study comparing two EVOO types found that although one exhibited higher oleocanthal and the other more oleacein, after seven months of storage oleacein decreased by approximately 75% and oleocanthal by 60%, while tyrosol and hydroxytyrosol concentrations rose correspondingly (Palla et al., 2018 ). The commercial samples analyzed in this study were at least six months old; storage conditions were unavailable. The relatively elevated hydroxytyrosol concentrations observed may result from this prolonged storage. Previous analyses of fresh, locally produced olive oils revealed the absence of hydroxytyrosol and tyrosol in most samples; tyrosol appeared in two samples and hydroxytyrosol in one, with concentrations not exceeding 4 mg kg⁻¹. A locally produced Picual sample analyzed within two weeks of extraction contained 1.64 ± 0.004 mg L⁻¹ tyrosol and 4.22 ± 0.004 mg L⁻¹ hydroxytyrosol. After one year, concentrations of these compounds increased markedly to 7.25 mg L⁻¹ and 86.46 mg L⁻¹, respectively (Al-Hashmi et al., 2025 ). From these observations, it can be inferred that fresh olive oil may possess stronger anti-inflammatory properties due to higher oleocanthal and oleacein content, while aged olive oil might provide enhanced cardioprotective benefits owing to increased levels of tyrosol and hydroxytyrosol. The total concentration of the ten phenolic compounds is summarized in Fig. 2 , varying across samples; Brand C displayed the highest total phenolic content (250.09 mg L⁻¹), whereas Brand A exhibited the lowest (116.13 mg L⁻¹). Comparison of total phenolic content via LC-MS/MS and the Folin-Ciocalteu (F-C) method revealed that the F–C assay typically produced higher values than LC-MS/MS analysis. This discrepancy likely arises from the capacity of the F–C reagent to oxidize non-phenolic organic and inorganic substances. Methodological and instrumental differences may also contribute (Bayram et al., 2012b ). Moreover, the LC-MS/MS method quantifies only the ten targeted phenolic compounds, while the F–C assay measures total phenolics. Several studies report strong correlations between these methods when applied to large sample sets (Alessandri et al., 2014 ; Andjelkovic et al., 2008 ; Luaces et al., 2021d). In contrast, this study noted a weak correlation, likely due to the limited sample size. These findings underscore that total phenolic content alone cannot serve as a definitive indicator of olive oil quality; comprehensive evaluation requires assessment of individual phenolic components. Comparison of the phenolic composition of EVOOs marketed in the Omani market with literature data from Mediterranean countries reveals both quantitative overlap and compositional divergence. According to published datasets covering Spain, Italy, Greece, Tunisia, Morocco, Turkey, and the broader Mediterranean region, total phenolic compound (TPC) in EVOOs spans an exceptionally wide range, from as low as 26 mg kg⁻¹ in commercial or highly processed oils to values exceeding 5000 mg kg⁻¹ in early-harvest Italian monovarietal oils analyzed by HPLC-DAD and MS-based techniques (Ben Mansour et al., 2022 ; Korkmaz, 2023 ; Korkmaz et al., 2025 ; Kritikou et al., 2021 ; Negro et al., 2019 ). Within this context, the TPC of Omani market EVOOs (517–1857 mg kg⁻¹) clearly overlaps with the upper-middle segment of Mediterranean oils, aligning closely with high-quality Italian, Arbequina, Turkish, and Tunisian EVOOs reported in the literature (Ben Mansour et al., 2022 ; Korkmaz, 2023 ; Korkmaz et al., 2025 ; Negro et al., 2019 ). This indicates that, despite prolonged storage and retail handling, Omani oils retain phenolic levels comparable to many premium Mediterranean products. These differences could mostly be due to the variety, maturity, and growing conditions of olives (Korkmaz, 2023 ). Essentially, in many previous studies on olive oils, TPC values calculated spectrophotometrically were lower than the sum of individual phenolic compounds identified by HPLC (Korkmaz, 2023 ). Literature data indicate that tyrosol concentrations in Mediterranean EVOOs generally fall within 0.1–208 mg kg⁻¹, with higher values typically associated with commercial or stored oils rather than freshly produced samples (Ben Mansour et al., 2022 ; Korkmaz, 2023 ; Kritikou et al., 2021 ; Negro et al., 2019 ). Tyrosol levels in Omani market EVOOs (0.7–3.59 mg kg⁻¹) fall within the lower Mediterranean range of commercial EVOOs analyzed by HPLC-DAD and LC-MS (Ben Mansour et al., 2022 ; Korkmaz, 2023 ; Kritikou et al., 2021 ). In contrast, hydroxytyrosol shows a distinctive pattern. Mediterranean literature values generally range from trace levels up to approximately 62 mg kg⁻¹ in fresh EVOOs, with higher concentrations reported in oils subjected to storage, phenolic enrichment, or secondary hydrolysis processes (Castillo-Luna & Priego-Capote, 2024 ; Kritikou et al., 2021 ; Negro et al., 2019 ). Omani market EVOOs exhibit comparatively elevated hydroxytyrosol concentrations (33.87–127.16 mg kg⁻¹), exceeding typical values reported for fresh Mediterranean oils and overlapping with or surpassing upper literature ranges. This enrichment is consistent with extensive hydrolysis of secoiridoid derivatives such as ligstroside aglycones during storage and commercial handling (Castillo-Luna & Priego-Capote, 2024 ; Kritikou et al., 2021 ; Negro et al., 2019 ). Flavonoid profiles further support the comparability of Omani EVOOs with Mediterranean oils. Literature reports show apigenin concentrations typically reaching 72.7 mg kg⁻¹ and luteolin values extending up to approximately 53 mg kg⁻¹ in Spanish and Italian EVOOs, respectively (Kritikou et al., 2021 ). Omani market samples, with apigenin (2.07–22.49 mg kg⁻¹) and luteolin (19.05–49.43 mg kg⁻¹), overlap with the moderate and upper ranges reported for Mediterranean oils, indicating strong flavonoid stability during storage. This behavior aligns with previous findings showing that flavones are more resistant to oxidative degradation than secoiridoid aldehydes (Korkmaz, 2023 ; Negro et al., 2019 ). Moreover, the TPC in EVOOs is affected by genetic as well as pre- and post-harvest factors (Korkmaz, 2023 ). With respect to lignans, pinoresinol concentrations reported in Mediterranean EVOOs typically range from non-detectable to approximately 23 mg kg⁻¹, depending on cultivar and processing conditions (Kritikou et al., 2021 ). The relatively low to moderate pinoresinol levels detected in Omani EVOOs (0.57–2.18 mg kg⁻¹) are consistent with values reported for commercial oils rather than freshly milled monovarietal EVOOs (Ben Mansour et al., 2022 ; Korkmaz, 2023 ; Kritikou et al., 2021 ). Overall, comparison with literature values demonstrates that Omani market EVOOs are not phenol-poor oils, but instead exhibit competitive total phenolic content and robust flavonoid levels, comparable to many Mediterranean EVOOs. The principal distinction lies in the shift from complex secoiridoids toward simpler phenols, particularly hydroxytyrosol, reflecting advanced phenolic transformation during storage. These trends are fully consistent with published evidence showing that cultivar, processing conditions, and storage environment shape the final phenolic profile of EVOOs, often outweighing geographic origin alone (Ben Mansour et al., 2022 ; Castillo-Luna & Priego-Capote, 2024 ; Korkmaz, 2023 ; Korkmaz et al., 2025 ; Kritikou et al., 2021 ; Negro et al., 2019 ). 4. Conclusion With regard to the increasing role of olive oil in culinary practices, along with the rise of cultivation and production of olive oil in Oman in recent years, we have attempted to analyze EVOOs in the Omani market. For this, six various brands, including international brands and two locally manufactured kinds, were analyzed for the phenolic profile and compared to previously assessed EVOOs. The findings demonstrate that the phenolic profile of EVOOs available in the Omani market aligns with the range of Mediterranean EVOOs, confirming that local and imported products maintain competitive phenolic levels despite climatic and storage challenges. The optimized extraction method, reinforced by machine learning-based feature importance analysis, underscores the critical role of solvent polarity and salt addition in maximizing phenolic recovery. Phenolic transformations during storage, notably the increase in hydroxytyrosol and tyrosol alongside the decline of oleocanthal and oleacein, reflect dynamic compositional changes affecting oil bioactivity. These insights emphasize that total phenolic content alone is insufficient to assess EVOO quality; detailed profiling of individual compounds is essential. Overall, this study establishes a valuable baseline for monitoring and improving the phenolic quality of olive oils in Oman, supporting both consumer health and the development of the nascent local olive oil industry. Declarations Competing Interests The authors declare no competing interests Author Contribution Azza A. H. Al Shamli: Methodology, Validation, Investigation, Data curation, Formal analysis, Writing – first draft, review and editing.Maryam Mousavizadegan: Data analysis and feature importance calculations, Writing - review and editing.Haider A. J. Al Lawati: Supervision, Project administration, Conceptualization, Resources, Writing – review and editing. Acknowledgement The authors would like to acknowledge the Ministry of High Education, Research and Innovation for their generous financial support through the RC/RG-SCI/CHEM/22/02. Data Availability The datasets generated and analyzed during the current study are available from the corresponding author upon reasonable request. References Abdu Hussen A (2022) High-performance liquid chromatography (HPLC): A review. Annals Adv Chem 6(1):10–20. ttps://doi.org/10.29328/journal.aac.1001026 Al-Busaidi M (2012) The struggle between nature and development: Linking local knowledge with sustainable natural resources management in Al-Jabal Al-Akhdar Region, Oman (Doctoral dissertation). British Library EThOS. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.564114 Alessandri S, Ieri F, Romani A (2014) Minor polar compounds in extra virgin olive oil: Correlation between HPLC-DAD-MS and the Folin–Ciocalteu spectrophotometric method. J Agric Food Chem 62(4):826–835. ttps://doi.org/10.1021/jf403104a Al-Hashmi ZH, Al-Lawati HAJ, Suliman FEO, Hassanzadeh J (2025) Quantitative estimation of pharmacologically relevant phenolic compounds in olive oils harvested in Jabal Al Akhdar in Oman. Food Chem Adv 6:100922. ttps://doi.org/10.1016/j.focha.2025.100922 Andjelkovic M, Van Camp J, Pedra M, Renders K, Socaciu C, Verhé R (2008) Correlations of the phenolic compounds and the phenolic content in some Spanish and French olive oils. J Agric Food Chem 56(13):5181–5187. ttps://doi.org/10.1021/jf0724419 Arrasco-Pancorbo A, Cruces-Blanco C, Segura-Carretero A, Fernández-Gutiérrez A (2004) Sensitive determination of phenolic acids in extra-virgin olive oil by capillary zone electrophoresis. J Agric Food Chem 52(22):6687–6693. ttps://doi.org/10.1021/jf058140l Bayram B, Esatbeyoglu T, Schulze N, Ozcelik B, Frank J, Rimbach G (2012b) Comprehensive analysis of polyphenols in 55 extra virgin olive oils by HPLC-ECD and their correlation with antioxidant activities. Plant Foods Hum Nutr 67(4):326–336. ttps://doi.org/10.1007/s11130-012-0315-z Behbahan AK, Al Lawati HAJ (2025) Bioactive phenols in olive samples: Evaluation of recent extraction methods. Sep Sci Plus 8(6):e70068. ttps://doi.org/10.1002/sscp.70068 Ben Mansour A, Gargouri B, Flamini G, Loubiri A, Taamalli A, Talhaoui N, Mohamed N, Segura-Carretero S, A., Zarrouk M (2022) Usefulness of phenolic profile in the classification of extra virgin olive oils from autochthonous and introduced cultivars in Tunisia. J Food Compos Anal 110:104548. ttps://doi.org/10.1016/j.jfca.2022.104548 Bonoli M, Bendini A, Cerretani L, Lercker G, Toschi TG (2004) Qualitative and semiquantitative analysis of phenolic compounds in extra virgin olive oils as a function of the ripening degree of olive fruits by different analytical techniques. J Agric Food Chem 52(23):7026–7032. ttps://doi.org/10.1021/jf048868m Castillo-Luna A, Priego-Capote F (2024) Phenolic enrichment of foods curated in olive oil: Kinetics and chemical evaluation. Curr Res Food Sci 7:100285. ttps://doi.org/10.1016/j.crfs.2024.100285 Cioffi G, Pesca MS, De Caprariis P, Braca A, Severino L, De Tommasi N (2010) Phenolic compounds in olive oil and olive pomace from Cilento (Campania, Italy) and their antioxidant activity. Food Chem 121(1):105–111. ttps://doi.org/10.1016/j.foodchem.2009.12.013 Criado-Navarro I, Ledesma-Escobar CA, Parrado-Martínez MJ, Marchal R (2022) Monitoring the partition of bioactive compounds in the extraction of extra virgin olive oil. LWT 162:113467. ttps://doi.org/10.1016/j.lwt.2022.113433 Eroglu E, Girgin SN (2021) A unique phenolic extraction method from olive oil macerate of Hypericum perforatum using DMSO: Assessment of in vitro anticancer activity, LC-MS/MS profile, total phenolic content and antioxidant capacity. South Afr J Bot 139:6–11. ttps://doi.org/10.1016/j.sajb.2021.01.015 Esposito Salsano J, Pinto D, Rodrigues F, Saba A, Manera C, Digiacomo M, Macchia M (2022) Oleocanthalic acid from extra-virgin olive oil: Analysis, preparative isolation and radical scavenging activity. J Food Compos Anal 105:104227. ttps://doi.org/10.3390/foods11091354 González AG, Herrador MÁ (2007) A practical guide to analytical method validation, including measurement uncertainty and accuracy profiles. TRAC Trends Anal Chem 26(3):227–238. ttps://doi.org/10.1016/j.trac.2007.01.009 Hrncirik K, Fritsche S (2004) Comparability and reliability of different techniques for the determination of phenolic compounds in virgin olive oil. Eur J Lipid Sci Technol 106(8):540–549. ttps://doi.org/10.1002/ejlt.200400942Digital Object Identifier (DOI) Korkmaz A (2023) Characterization and comparison of extra virgin olive oils of Turkish olive cultivars. Foods 12:349. ttps://doi.org/10.3390/foods12020349 Korkmaz A, Unsal V, Yıldız R, Oner E, Atasoy AF (2025) Chemical evaluation of Arbequina extra virgin olive oil with in silico analysis of its key phenolic compounds targeting LDL metabolism. Sci Rep 15:18144. ttps://doi.org/10.1038/s41598-025-18144 Kritikou E, Kalogiouri NP, Kostakis M, Kanakis D-C, Martakos I, Lazarou C, Pentogennis M, Thomaidis NS (2021) Geographical characterization of olive oils from the North Aegean region based on the analysis of biophenols with UHPLC-QTOF-MS. Foods 10(9):2102. ttps://doi.org/10.3390/foods10092102 Luaces P, Pascual M, Pérez AG, Sanz C (2021a) An easy-to-use procedure for the measurement of total phenolic compounds in olive fruit. Antioxidants 10(11):1656. ttps://doi.org/10.3390/antiox10111656 Medina S, Auñón D, Lehoux J, Durand T, Crauste C, Gil-Izquierdo Á (2022) Hydroxytyrosol fatty acid esters as new candidate markers for detecting olive oil inadequate storage conditions by UHPLC-QqQ-MS/MS. Microchem J 181:107772. ttps://doi.org/10.1016/j.microc.2022.107656 Negro C, Aprile A, Luvisi A, Nicolì F, Nutricati E, Vergine M, Miceli A, Blando F, Sabella E, De Bellis L (2019) Phenolic profile and antioxidant activity of Italian monovarietal extra virgin olive oils. Antioxidants 8(6) Article 161. ttps://doi.org/10.3390/antiox8060161 Palla M, Digiacomo M, Cristani C, Bertini S, Giovannetti M, Macchia M, Manera C, Agnolucci M (2018) Composition of health-promoting phenolic compounds in two extra virgin olive oils and diversity of associated yeasts. J Food Compos Anal 74:27–33. ttps://doi.org/10.1016/j.jfca.2018.08.008 Sicari V (2017) Antioxidant potential of extra virgin olive oils extracted from three different varieties cultivated in the Italian province of Reggio Calabria. J Appl Bot Food Qual 90:86–91. ttps://doi.org/10.5073/jabfq.2017.090.011 Tasioula-Margari M, Tsabolatidou E (2015) Extraction, separation, and identification of phenolic compounds in virgin olive oil by HPLC-DAD and HPLC-MS. Antioxidants 4(3):548–562. ttps://doi.org/10.3390/antiox4030548 Tripoli E, Giammanco M, Tabacchi G, Di Majo D, Giammanco S, La Guardia M (2005) The phenolic compounds of olive oil: Structure, biological activity and beneficial effects on human health. Nutr Res Rev 18(1):98–112. ttps://doi.org/10.1079/NRR200495 Additional Declarations No competing interests reported. Supplementary Files SupplementaryInformation11.docx Cite Share Download PDF Status: Under Revision Version 1 posted Editorial decision: Revision requested 09 May, 2026 Reviews received at journal 04 May, 2026 Reviews received at journal 26 Apr, 2026 Reviewers agreed at journal 14 Apr, 2026 Reviewers agreed at journal 12 Apr, 2026 Reviewers agreed at journal 09 Apr, 2026 Reviewers invited by journal 09 Apr, 2026 Editor assigned by journal 17 Mar, 2026 Submission checks completed at journal 17 Mar, 2026 First submitted to journal 13 Mar, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Al","lastName":"Shamli¹","suffix":""},{"id":622727406,"identity":"66a2094f-65e1-492e-bcde-5acc39194e25","order_by":1,"name":"Maryam Mousavizadegan¹","email":"","orcid":"","institution":"Sultan Qaboos University","correspondingAuthor":false,"prefix":"","firstName":"Maryam","middleName":"","lastName":"Mousavizadegan¹","suffix":""},{"id":622727410,"identity":"e0112e2b-1c8d-484f-acb7-e536474616d5","order_by":2,"name":"Haider A. J. Al Lawati¹","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAzUlEQVRIiWNgGAWjYBACAwbGBgkGBgs5CJeNeC0SxqRoAaoHosQGorWYsx9uvPFxj0T6/PYcA4YPZYcZ+MUO4Ndi2ZPYbDnjmUTuhjNvDBhnnDvMIDk7gYDDDiS2SfMcAGqRyDFg5m07zGBwm5CW8w/bpP8ckEiXnwHU8pcoLTeAtjAckEhguAHUwkiclofNlj0HJAw3nHlWcLDnXDoPYb+cT39448cBG3n59uSND36UWcvxSxPQggQSGA4ASR6i1YO1jIJRMApGwSjACgDYLkWLuQPnpAAAAABJRU5ErkJggg==","orcid":"","institution":"Sultan Qaboos University","correspondingAuthor":true,"prefix":"","firstName":"Haider","middleName":"A. J. Al","lastName":"Lawati¹","suffix":""}],"badges":[],"createdAt":"2026-03-13 18:09:10","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9117332/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9117332/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":107481774,"identity":"2fae6634-7e32-490c-bcca-df16b1b1b667","added_by":"auto","created_at":"2026-04-22 02:19:55","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":39345,"visible":true,"origin":"","legend":"\u003cp\u003eQuantitative analysis of the ten targeted phenolic compounds across the six olive oil samples A, B, C, D, E and F.\u003c/p\u003e","description":"","filename":"Picture1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9117332/v1/eb72868e40277193b34235f7.jpg"},{"id":107481890,"identity":"4348e82f-4005-43f8-ad9b-e078c00ab6e2","added_by":"auto","created_at":"2026-04-22 02:20:43","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":32780,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of total phenolic content using LC-MS/MS and F-C methods.\u003c/p\u003e","description":"","filename":"Picture2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9117332/v1/9c71748b4b6f96bb351bf944.jpg"},{"id":107705180,"identity":"dea503bb-6f96-4656-96cb-45afd3f64ebf","added_by":"auto","created_at":"2026-04-24 09:09:03","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":343741,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9117332/v1/da9cb79f-6874-4266-aed3-e449a39d57fc.pdf"},{"id":107188036,"identity":"e858d771-0a92-43f1-83a3-95587c153dd2","added_by":"auto","created_at":"2026-04-17 19:43:19","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":188015,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryInformation11.docx","url":"https://assets-eu.researchsquare.com/files/rs-9117332/v1/4e28171b354d34874d64feac.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Phenolic Profile Characterization of Extra Virgin Olive Oils from the Omani Market Using a Salt-Assisted Extraction and LC-MS/MS Approach","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eOlive oil, obtained through the mechanical extraction of the fruit of \u003cem\u003eOlea europaea L.\u003c/em\u003e, member of the Oleaceae family, has become an inseparable component in most culinary routines. It mainly consists of a glycerol fraction, comprising about 90\u0026ndash;99%, alongside a non-glycerol fraction that ranges from 0.4% to 5%. Oleic acid represents roughly 70\u0026ndash;80% of the fatty acids present in olive oil (Tripoli et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). The beneficial properties of olive oil are largely attributed to the antioxidant effects of its components (Tripoli et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). Extra virgin olive oil (EVOO) primarily contains volatile compounds, aliphatic and triterpenic alcohols, sterols, and various antioxidants. Among these, phenolic compounds stand out as a particularly abundant family of antioxidants in EVOO. These compounds fall into several classes, with the most prominent being simple phenols, phenolic acids, phenolic alcohols, hydroxyisochromans, secoiridoids, lignans, and flavonoids (Tripoli et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2005\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eExtra virgin olive oil production has only recently begun in Oman, mainly around Jabal Al Akhdar (JA) in the northern part of the country, within Al Dakhiliyah Governorate. JA stretches about 80 km long and 32 km wide, sitting at an elevation of 2000 meters above sea level (Al-Busaidi, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). The region is characterized by a Mediterranean climate, with average air temperatures ranging from 7.4 to 23.0\u0026deg;C and ground temperatures between 7.9 and 23.7\u0026deg;C (Al-Busaidi, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). In 2012, approximately 15,000 olive trees were cultivated in JA (Al-Busaidi, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). According to data from Oman\u0026rsquo;s Ministry of Agriculture and Fisheries, a total of sixty tons of olives were harvested during the period from August to December 2019. This harvest yielded roughly 8,000 liters of EVOO, valued at OMR 160,000, based on a price of OMR 20 per liter (Al-Hashmi et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). It is well known that the chemical composition of EVOO is highly sensitive to storage conditions, especially heat and sunlight (Medina et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Given the harsh climate of Oman, with temperatures exceeding 50\u0026deg;C during summer and intense sunshine, quality control and phenolic content assessment of olive oil in the Omani market is critical.\u003c/p\u003e \u003cp\u003eDifferent liquid\u0026ndash;liquid extraction methods have been reported using a variety of solvents to isolate phenolic compounds from olive oil (Bonoli et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Hrncirik \u0026amp; Fritsche, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Arrasco-Pancorbo et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Garc\u0026iacute;a-Villalba et al., 2010; Cioffi et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Luaces et al., 2021; Eroglu \u0026amp; Girgin, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2021\u003c/span\u003e.; Behbahan \u0026amp; Al Lawati, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). Common solvents include methanol\u0026ndash;water mixtures at ratios such as 60:40 or 80:20 (v/v), which effectively extract the hydroalcoholic phase from oil samples (Bonoli et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Hrncirik \u0026amp; Fritsche, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Arrasco-Pancorbo et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). Hexane or n-hexane is often employed as the non-polar solvent to separate oil fractions and aid in recovering phenolic compounds (Bonoli et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Hrncirik \u0026amp; Fritsche, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Arrasco-Pancorbo et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). Acetonitrile is also used to dissolve and wash extracts, improving selectivity during extraction (Garc\u0026iacute;a-Villalba et al., 2010). Dimethyl sulfoxide has been suggested as an alternative solvent for extracting phenolics from olive fruit and macerates, demonstrating effectiveness in isolating diverse phenolic derivatives (Luaces et al., 2021). Additionally, blends of organic solvents such as ethanol\u0026ndash;chloroform\u0026ndash;acetone\u0026ndash;water mixtures are used for thorough extraction from both oil and solid olive matrices (Criado-Navarro et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). These solvent systems are chosen to maximize phenolic recovery while ensuring compatibility with subsequent chromatographic and spectrometric analyses (Behbahan \u0026amp; Al Lawati, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2025\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn this study, phenolic extraction optimization is carried out and the addition of sodium chloride to the extraction solvent was tested to assess its impact on phenolic extraction. We then used feature importance via machine learning techniques, specifically Random Forest's mean decreases impurity (MDI) and SHAP (SHapley Additive exPlanations) to better gain insight on how various parameters can impact the efficiency of phenolic extraction. The optimized extraction technique was then applied to develop an LC/MS/MS method for detecting 10 phenolic compounds in olive oil, including hydroxytyrosol, tyrosol, luteolin, oleuropein, apigenin, diosmetin, pinoresinol, p-coumaric acid, oleacein, and oleocanthal. Finally, the method was used to analyze six commercial olive oil samples from the local market, two of which were produced locally in the Sultanate of Oman. This study represents the first report evaluating the phenolic content of olive oil from the Omani market and comparing it with other olive oils documented in the literature.\u003c/p\u003e"},{"header":"2. Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Samples\u003c/h2\u003e \u003cp\u003eEVOO samples were obtained from local markets located in Muscat, Oman. A batch of 0.5 L of six brands EVOO were collected. Brand A (Production date, 05/2025), B (production date, 04/2025), C (production date, 02/2025). These three brands were Spanish originated olive oil. Brand D (production date 03/2024) was Tunisian EVOO and Brands E (production date, 05/2025) and F (October 2024) were locally produced. The samples were transported immediately to the laboratory and analyzed directly. The remaining was stored in amber glass bottles at 20\u0026deg;C for further analyses if needed.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Chemicals\u003c/h2\u003e \u003cp\u003eAnalytical standards of hydroxytyrosol, tyrosol, p-coumaric acid, ferulic acid, luteolin, apigenin, pinoresinol, diosmetin, oleacein, oleocanthal, oleuropein, and caffeic acid were purchased from PhytoLab (Germany) and Sigma-Aldrich (UK). Caffeic acid\u0026mdash;an analyte not naturally present in Olea europaea\u0026mdash;was selected and used as an internal standard (IS).\u003c/p\u003e \u003cp\u003eIndividual stock solutions were prepared by dissolving 10 mg of each pure standard in 10 mL of methanol to obtain concentrations of 1000 mg/L. A composite standard solution (100 mg/L for each analyte) was prepared by mixing appropriate aliquots of the individual stock solutions and diluting with methanol. All standard solutions were stored at 5\u0026deg;C and equilibrated to room temperature prior to use. Working individual and mixed standard solutions were prepared by further dilution with methanol or water, stored at 4\u0026deg;C, and freshly prepared on a weekly basis.\u003c/p\u003e \u003cp\u003eAll organic solvents, reagents, and salts were of analytical or HPLC grade and procured from Sigma-Aldrich (UK). Ultrapure water was produced using a Milli-Q SP Water System (Millipore, USA). Folin\u0026ndash;Ciocalteu reagent, sodium carbonate, and gallic acid were purchased from VWR International (France). A vortex mixer (Whirlimixer, England) and a centrifuge (Labdex, UK) were used for sample preparation throughout the study.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Extraction of phenolic compounds from EVOO and feature importance\u003c/h2\u003e \u003cp\u003eA 3.0 g aliquot of EVOO was weighed into a centrifuge tube, followed by addition of 3.0 mL n-hexane and 1.5 mL of methanol: water: NaCl (80:20:10 v/v). Subsequently, 10 \u0026micro;L of caffeic acid (IS) was added. The mixture was vortexed for 5 min and centrifuged for 10 min at 1000 rpm.\u003c/p\u003e \u003cp\u003eThe hydroalcoholic phase was collected, and the hexane layer was re-extracted twice using 1.5 mL methanol: water (80:20, v/v). The combined extracts were filtered through 0.22 \u0026micro;m nylon filters before HPLC/LC-MS/MS analysis. Each sample was extracted in triplicate (n\u0026thinsp;=\u0026thinsp;3).\u003c/p\u003e \u003cp\u003eTo evaluate the impact of the various experimental parameters on the efficiency of the phenolic extraction, two complementary machine learning (ML) approaches were implemented for feature importance analysis including Mean Decrease in Impurity (MDI) and SHapley Additive exPlanations (SHAP) methods. For this, each experiment was described using polarity index of the solvent, dipole moment, ratio of solvent, percentage of NaCl and overall system polarity. MDI is a method used in tandem with tree-based learners and it measures how each variable reduces prediction error across decision trees splits. SHAP quantifies the contribution of each feature to individual predictions using game-theoretic Shapley values for model-consistent interpretability. All ML calculations were carried out on Python 3.14 using the scikit-learn package. First, a Random Forest regressor with 100 trees and a fixed random seed was developed. Using the algorithms built-in impurity-based feature importance method (MDI), the contribution of various parameters was evaluated and the resulting importance scores were extracted. SHAP analysis was also performed for further assessment of feature importance. After the Random Forest regression model was developed, SHAP values were computed using the TreeExplainer method to attain game-theoretic estimates of the contribution of each feature on total extracted phenolic compound values. Mean absolute SHAP values were thus extracted and ranked. The Python scripts used for Random Forest modeling and SHAP analysis are available from the corresponding author upon reasonable request.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4. Preparation of standards\u003c/h2\u003e \u003cp\u003eCalibration curves were constructed using standard solutions of hydroxytyrosol, tyrosol, p-coumaric acid, ferulic acid, luteolin, apigenin, pinoresinol, diosmetin, oleacein, oleocanthal, oleuropein, and caffeic acid.\u003c/p\u003e \u003cp\u003eStock standard solutions (1000 mg/L) were prepared by dissolving 10 mg of each compound in 100 mL water or methanol. Calibration curves were generated by plotting peak area versus concentration.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5. LC-MS/MS analysis\u003c/h2\u003e \u003cp\u003eAn LC-MS/MS system (Shimadzu, Japan) equipped with an LC-2040 pump, LC-2040 autosampler, LC-2040 oven and an ESI source was used. The ESI source parameters were set as follows: capillary voltage, \u0026minus;\u0026thinsp;3500 V (+\u0026thinsp;3500 V); sheath gas flow rate, 11 L min⁻\u0026sup1;; sheath gas temperature, 350\u0026deg;C; nebulizer pressure, 35 psi; drying gas temperature, 150\u0026deg;C; drying gas flow rate, 15 L min⁻\u0026sup1;; and fragmentor voltage, 360 V. Nitrogen was used as the nebulizer, drying, and collision gas. Mass spectra were acquired over an m/z range of 100\u0026ndash;1100.\u003c/p\u003e \u003cp\u003eCompound identity was confirmed using retention times, accurate mass, and fragmentation patterns, and through co-injection with commercial standards. Separation was achieved using a reversed-phase C18 Eclipse Plus column (3.5 \u0026micro;m, 2.1 mm \u0026times; 100 mm).\u003c/p\u003e \u003cp\u003eA gradient elution program (Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e) was employed using a binary mobile phase consisting of (A) methanol containing 0.1% trifluoroacetic acid (TFA) and (B) water containing 0.1% TFA. The flow rate was maintained at 0.2 mL min⁻\u0026sup1;, with an injection volume of 10 \u0026micro;L. The column temperature was set at 50\u0026deg;C.\u003c/p\u003e \u003cp\u003eLabSolution software (version 5.82) was used for data acquisition, post-run analysis and peak characterization.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e2.6. Recovery Study\u003c/h2\u003e \u003cp\u003eRecovery of phenolic compounds was evaluated by spiking EVOO/hexane solutions with standards at levels approximately 3\u0026ndash;5 times the natural concentration.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e2.7. Determination of total phenolic content\u003c/h2\u003e \u003cp\u003eTotal phenolic content was determined using the Folin\u0026ndash;Ciocalteu spectrophotometric method (Shimadzu UV-VIS 1900, Kyoto, Japan). A 0.1 mL aliquot of the extract was mixed with 2.5 mL of 1:10 diluted Folin\u0026ndash;Ciocalteu reagent and allowed to stand for 8 min. Subsequently, 2.0 mL of 7.5% Na₂CO₃ was added, and the mixture was incubated for 30 min in the dark. Absorbance was measured at 760 nm.\u003c/p\u003e \u003cp\u003eQuantification was performed using a gallic acid calibration curve (50\u0026ndash;500 mg kg⁻\u0026sup1;; r\u0026sup2; = 0.996). Results were expressed as mg gallic acid equivalents (GAE) per kg of oil. Each extract was analyzed in triplicate.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Sample preparation and quality evaluation\u003c/h2\u003e \u003cp\u003eGiven the increasing market of olive oil production in Oman, and considering Oman\u0026rsquo;s harsh climate especially in summer where temperature can reach 50\u0026deg;C. Such high temperatures may affect negatively the quality of EVOO during storage, we have attempted to evaluate the quality of olive oil in Omani market in terms of phenolic content richness compared to other markets. The Omani market, like other international markets, offers a range of commercial olive oils which were used in comparison with two locally produced Omani EVOO samples. The two samples analyzed in this study include one from a single cultivar (Picual) (Brand F) and the other a blend of multiple cultivars (Brand E).\u003c/p\u003e \u003cp\u003eThe analysis of the olive oil samples based on acid value and peroxide value provides insightful information regarding their quality and oxidative state. Acid value (AV) is a critical parameter reflecting the level of free fatty acids, which increase as a result of hydrolytic degradation. The values observed across all six samples ranged from 0.01% to 0.11%, significantly below the internationally recognized threshold of 0.8% for EVOO (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). These low acid values indicate that the oils have undergone minimal hydrolysis, suggesting good handling practices and preservation of oil integrity from production to analysis.\u003c/p\u003e \u003cp\u003ePeroxide value (PV) serves as an indicator of primary oxidation products, revealing the extent to which the oils have undergone oxidative deterioration. The peroxide values measured in Samples A, B, and C were 9.90, 11.93, and 9.94 meq O₂ kg⁻\u0026sup1; respectively (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). While all these values fall within acceptable limits for fresh olive oil, the relatively elevated PV in Sample B suggests a higher degree of oxidation compared to Samples A and C. This may be attributed to factors such as prolonged exposure to oxygen, light or suboptimal storage conditions. On the other hand, Samples D, E and F exhibited undetectable peroxide values, indicating exceptional freshness and minimal exposure to oxidative stress.\u003c/p\u003e \u003cp\u003eThe combined interpretation of acid and peroxide values suggests that all samples meet the quality standards for EVOO, with samples 4, 5 and 6 demonstrating superior preservation of freshness and oxidative stability. The variation in peroxide values among the samples highlights the sensitivity of olive oil to environmental factors influencing lipid oxidation. This underscores the importance of proper storage and handling to maintain oil quality over time.\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\u003eAcid value and peroxide value of olive oil samples\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAcid value (% as oleic acid)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePeroxide value (meq O₂ kg⁻\u0026sup1;)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.09\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e9.90\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e11.93\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e9.94\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eD\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eND\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eE\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eND\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eND\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eND, not detected.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Optimization of phenolic extraction\u003c/h2\u003e \u003cp\u003eVarious extraction techniques have been reported for isolating phenolic compounds from olive oil, using different solvents or solvent mixtures such as methanol, ethanol, or acetonitrile combined with water at varied concentrations (Behbahan \u0026amp; Al Lawati, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). In this study, the addition of sodium chloride (NaCl) at concentrations between 10 and 20% (w/v) to the extraction solvent resulted in a 20 to 30% improvement in extraction efficiency.\u003c/p\u003e \u003cp\u003eInitially, a solvent containing 60% methanol was employed to extract phenolic compounds from olive oil. The phenolic content was quantified using the Folin-Ciocalteu (FC) method, yielding an average concentration of 400\u0026thinsp;\u0026plusmn;\u0026thinsp;13 ppm (relative standard deviation, RSD, 3%) across three replicates. Upon the addition of 20% (w/v) NaCl to this solvent system, the phenolic content significantly increased to 517\u0026thinsp;\u0026plusmn;\u0026thinsp;44 ppm (RSD 2%). Further testing of varying methanol and NaCl concentrations revealed that an 80% methanol solvent combined with 10% NaCl achieved the highest extraction efficiency, with a low RSD of 0.1% (520\u0026thinsp;\u0026plusmn;\u0026thinsp;3 ppm).\u003c/p\u003e \u003cp\u003eA similar trend was observed when using acetonitrile; the addition of 20% (w/v) NaCl to 80% acetonitrile improved extraction efficiency by approximately 20%. Conversely, using ethanol as the organic solvent reduced extraction efficiency to 392\u0026thinsp;\u0026plusmn;\u0026thinsp;18 ppm (RSD 1.1%). Increasing the water content to 40% ethanol with 20% (w/v) NaCl did not enhance extraction efficiency, resulting in 292\u0026thinsp;\u0026plusmn;\u0026thinsp;13 ppm (RSD 1.2%).\u003c/p\u003e \u003cp\u003eTo assess the influence of multiple factors\u0026mdash;including the type and concentration of the organic solvent, NaCl concentration, and overall solution polarity\u0026mdash;machine learning-based feature importance analyses were conducted using Random Forest mean decrease impurity (MDI) and SHapley Additive exPlanations (SHAP) methods. Both analyses identified the overall polarity of the extraction system as the most critical variable, influenced directly by solvent type, NaCl concentration, and solvent volume (Figure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). Additionally, both the organic solvent amount and NaCl concentration ranked as significant contributors. These results indicate that the total polarity of the system is pivotal for enhancing phenolic compound extraction. Although NaCl does not directly increase the polarity of water molecules, it induces strong ion-dipole interactions that can alter the behavior of the solution, effectively increasing its overall polarity. This phenomenon also explains the reduced extraction efficiency observed with ethanol, which exhibits lower polarity than methanol and acetonitrile. The Python scripts used for Random Forest modeling and SHAP analysis are available from the corresponding author upon reasonable request.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.3. LC\u0026ndash;MS/MS method development and validation\u003c/h2\u003e \u003cp\u003eA liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for phenolic compound analysis. While p-coumaric acid is commonly used as an internal standard, its presence in the olive oil samples here necessitated the use of caffeic acid as the internal standard instead.\u003c/p\u003e \u003cp\u003ePrior to quantification, the identification of the ten phenolic compounds was confirmed via LC-MS/MS, based on retention times, molecular masses, and daughter ion profiles. The data obtained from the MS/MS detector are provided in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and Figure S2 shows the mass spectra of daughter ions (m/z) of the 10 components.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eRetention time and MS/MS parameters of phenolic compounds\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" 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=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCompound\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePrecursor ion (m/z)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRetention time (min)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDaughter ions (m/z)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCaffeic acid (IS)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e179\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e90, 115, 135\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ep-Coumaric acid\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e163\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e90, 93, 117, 119\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHydroxytyrosol\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e153\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e69, 108, 109, 115, 123\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTyrosol\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e137\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e7.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e106, 119\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOleacein\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e319\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e11.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e69\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePinoresinol\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e357\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e12.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e136, 151, 311, 342\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOleocanthal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e303\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e12.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e59\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLuteolin\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e285\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e13.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e107, 133, 135, 151\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eApigenin\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e269\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e14.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e107, 117, 149\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDiosmetin\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e299\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e14.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e135, 284\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOleuropein\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e539\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e21.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e307, 377\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe performance of the analytical method was validated using standard solutions of the phenolic compounds, evaluating precision, linearity, accuracy, limit of detection (LOD), and limit of quantitation (LOQ). Precision was maintained through triplicate injections. Calibration curves constructed with 8\u0026ndash;10 concentration points ranging from 0.01 to 10 mg kg⁻\u0026sup1; displayed strong linearity for all compounds, confirming method reliability and precision.\u003c/p\u003e \u003cp\u003eAccuracy of the extraction was assessed by determining recovery rates through spiking EVOO/hexane solutions with phenolic standards at levels approximately three to five times the natural concentrations. The recovery was calculated as:\u003c/p\u003e \u003cp\u003eRecovery (%) = ((\u003cem\u003eC\u003c/em\u003e_found\u0026thinsp;\u0026minus;\u0026thinsp;\u003cem\u003eC\u003c/em\u003e_original) / \u003cem\u003eC\u003c/em\u003e_spiked) \u0026times; 100 (1)\u003c/p\u003e \u003cp\u003eWhere C is the concentration. All recovery measurements were performed in triplicate.\u003c/p\u003e \u003cp\u003eThe results indicated that the average percentage recovery values for the ten phenolic compounds ranged from 75% for diosmetin to 138% for oleacein, demonstrating the reliability and consistency of the extraction method employed.\u003c/p\u003e \u003cp\u003eThe limit of detection (LOD) is a critical analytical parameter, defined as the lowest analyte concentration that can be distinguished from background noise, typically set at three times the noise level. Meanwhile, the limit of quantification (LOQ) refers to the lowest analyte concentration that can be measured with acceptable accuracy and precision, established by analyzing at least ten sample blanks and applying a factor of ten to ensure reliable quantification (Gonz\u0026aacute;lez \u0026amp; Herrador, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). The lowest LOD values observed were 0.002 mg L⁻\u0026sup1; for tyrosol, oleacein, luteolin, apigenin, and diosmetin, while the highest was 0.02 mg L⁻\u0026sup1; for pinoresinol. LOQ values ranged from 0.006 to 0.060 mg L⁻\u0026sup1;. A summary of all validation parameters is provided in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e3.4. Separation and quantification of phenolic compounds by LC-MS/MS\u003c/h2\u003e \u003cp\u003eThis study focused on ten primary phenolic compounds. Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e lists their retention times. The elution order generally reflects differences in polarity and molecular structure; less polar compounds experience longer retention times, enabling separation based on these differences (Abdu Hussen, \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Phenolic acids, which exhibit high polarity due to partial charges at neutral pH, elute first. Hydroxytyrosol, a relatively hydrophilic phenolic compound with a single hydroxyl group, follows the phenolic acids in elution order. Tyrosol, structurally similar but slightly more hydrophobic, elutes subsequent to hydroxytyrosol. More hydrophobic compounds such as oleacein, oleocanthal, pinoresinol, luteolin, apigenin, and diosmetin interact more strongly with the stationary phase, resulting in later elution times. Oleuropein, the largest molecule with the greatest number of interaction sites, elutes last at approximately 21.9 minutes.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e presents the quantitative analysis of the ten targeted phenolic compounds across six olive oil samples. Hydroxytyrosol, oleocanthal, and luteolin were consistently the most abundant compounds in all samples.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAmong the ten compounds analyzed, oleocanthal, oleacein, hydroxytyrosol, and tyrosol are recognized for their therapeutic properties (Tasioula-Margari \u0026amp; Tsabolatidou, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Hydroxytyrosol and tyrosol exhibit cardioprotective effects, while oleocanthal and oleacein possess potent anti-inflammatory activities. Literature reports indicate that phenolic compound concentrations shift during EVOO storage: oleocanthal and oleacein decrease, whereas simpler phenols such as tyrosol and hydroxytyrosol increase. This increase is attributed to the breakdown of more complex secoiridoid derivatives over time (Alessandri et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Luaces et al., 2021d; Palla et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Sicari, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). One study comparing two EVOO types found that although one exhibited higher oleocanthal and the other more oleacein, after seven months of storage oleacein decreased by approximately 75% and oleocanthal by 60%, while tyrosol and hydroxytyrosol concentrations rose correspondingly (Palla et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). The commercial samples analyzed in this study were at least six months old; storage conditions were unavailable. The relatively elevated hydroxytyrosol concentrations observed may result from this prolonged storage.\u003c/p\u003e \u003cp\u003ePrevious analyses of fresh, locally produced olive oils revealed the absence of hydroxytyrosol and tyrosol in most samples; tyrosol appeared in two samples and hydroxytyrosol in one, with concentrations not exceeding 4 mg kg⁻\u0026sup1;. A locally produced Picual sample analyzed within two weeks of extraction contained 1.64\u0026thinsp;\u0026plusmn;\u0026thinsp;0.004 mg L⁻\u0026sup1; tyrosol and 4.22\u0026thinsp;\u0026plusmn;\u0026thinsp;0.004 mg L⁻\u0026sup1; hydroxytyrosol. After one year, concentrations of these compounds increased markedly to 7.25 mg L⁻\u0026sup1; and 86.46 mg L⁻\u0026sup1;, respectively (Al-Hashmi et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2025\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eFrom these observations, it can be inferred that fresh olive oil may possess stronger anti-inflammatory properties due to higher oleocanthal and oleacein content, while aged olive oil might provide enhanced cardioprotective benefits owing to increased levels of tyrosol and hydroxytyrosol.\u003c/p\u003e \u003cp\u003eThe total concentration of the ten phenolic compounds is summarized in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, varying across samples; Brand C displayed the highest total phenolic content (250.09 mg L⁻\u0026sup1;), whereas Brand A exhibited the lowest (116.13 mg L⁻\u0026sup1;).\u003c/p\u003e \u003cp\u003eComparison of total phenolic content via LC-MS/MS and the Folin-Ciocalteu (F-C) method revealed that the F\u0026ndash;C assay typically produced higher values than LC-MS/MS analysis. This discrepancy likely arises from the capacity of the F\u0026ndash;C reagent to oxidize non-phenolic organic and inorganic substances. Methodological and instrumental differences may also contribute (Bayram et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2012b\u003c/span\u003e). Moreover, the LC-MS/MS method quantifies only the ten targeted phenolic compounds, while the F\u0026ndash;C assay measures total phenolics. Several studies report strong correlations between these methods when applied to large sample sets (Alessandri et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Andjelkovic et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Luaces et al., 2021d). In contrast, this study noted a weak correlation, likely due to the limited sample size.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThese findings underscore that total phenolic content alone cannot serve as a definitive indicator of olive oil quality; comprehensive evaluation requires assessment of individual phenolic components.\u003c/p\u003e \u003cp\u003eComparison of the phenolic composition of EVOOs marketed in the Omani market with literature data from Mediterranean countries reveals both quantitative overlap and compositional divergence. According to published datasets covering Spain, Italy, Greece, Tunisia, Morocco, Turkey, and the broader Mediterranean region, total phenolic compound (TPC) in EVOOs spans an exceptionally wide range, from as low as 26 mg kg⁻\u0026sup1; in commercial or highly processed oils to values exceeding 5000 mg kg⁻\u0026sup1; in early-harvest Italian monovarietal oils analyzed by HPLC-DAD and MS-based techniques (Ben Mansour et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Korkmaz, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Korkmaz et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2025\u003c/span\u003e; Kritikou et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Negro et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Within this context, the TPC of Omani market EVOOs (517\u0026ndash;1857 mg kg⁻\u0026sup1;) clearly overlaps with the upper-middle segment of Mediterranean oils, aligning closely with high-quality Italian, Arbequina, Turkish, and Tunisian EVOOs reported in the literature (Ben Mansour et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Korkmaz, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Korkmaz et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2025\u003c/span\u003e; Negro et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThis indicates that, despite prolonged storage and retail handling, Omani oils retain phenolic levels comparable to many premium Mediterranean products. These differences could mostly be due to the variety, maturity, and growing conditions of olives (Korkmaz, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Essentially, in many previous studies on olive oils, TPC values calculated spectrophotometrically were lower than the sum of individual phenolic compounds identified by HPLC (Korkmaz, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eLiterature data indicate that tyrosol concentrations in Mediterranean EVOOs generally fall within 0.1\u0026ndash;208 mg kg⁻\u0026sup1;, with higher values typically associated with commercial or stored oils rather than freshly produced samples (Ben Mansour et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Korkmaz, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Kritikou et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Negro et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Tyrosol levels in Omani market EVOOs (0.7\u0026ndash;3.59 mg kg⁻\u0026sup1;) fall within the lower Mediterranean range of commercial EVOOs analyzed by HPLC-DAD and LC-MS (Ben Mansour et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Korkmaz, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Kritikou et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn contrast, hydroxytyrosol shows a distinctive pattern. Mediterranean literature values generally range from trace levels up to approximately 62 mg kg⁻\u0026sup1; in fresh EVOOs, with higher concentrations reported in oils subjected to storage, phenolic enrichment, or secondary hydrolysis processes (Castillo-Luna \u0026amp; Priego-Capote, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Kritikou et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Negro et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Omani market EVOOs exhibit comparatively elevated hydroxytyrosol concentrations (33.87\u0026ndash;127.16 mg kg⁻\u0026sup1;), exceeding typical values reported for fresh Mediterranean oils and overlapping with or surpassing upper literature ranges. This enrichment is consistent with extensive hydrolysis of secoiridoid derivatives such as ligstroside aglycones during storage and commercial handling (Castillo-Luna \u0026amp; Priego-Capote, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Kritikou et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Negro et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eFlavonoid profiles further support the comparability of Omani EVOOs with Mediterranean oils. Literature reports show apigenin concentrations typically reaching 72.7 mg kg⁻\u0026sup1; and luteolin values extending up to approximately 53 mg kg⁻\u0026sup1; in Spanish and Italian EVOOs, respectively (Kritikou et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Omani market samples, with apigenin (2.07\u0026ndash;22.49 mg kg⁻\u0026sup1;) and luteolin (19.05\u0026ndash;49.43 mg kg⁻\u0026sup1;), overlap with the moderate and upper ranges reported for Mediterranean oils, indicating strong flavonoid stability during storage. This behavior aligns with previous findings showing that flavones are more resistant to oxidative degradation than secoiridoid aldehydes (Korkmaz, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Negro et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Moreover, the TPC in EVOOs is affected by genetic as well as pre- and post-harvest factors (Korkmaz, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eWith respect to lignans, pinoresinol concentrations reported in Mediterranean EVOOs typically range from non-detectable to approximately 23 mg kg⁻\u0026sup1;, depending on cultivar and processing conditions (Kritikou et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). The relatively low to moderate pinoresinol levels detected in Omani EVOOs (0.57\u0026ndash;2.18 mg kg⁻\u0026sup1;) are consistent with values reported for commercial oils rather than freshly milled monovarietal EVOOs (Ben Mansour et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Korkmaz, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Kritikou et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eOverall, comparison with literature values demonstrates that Omani market EVOOs are not phenol-poor oils, but instead exhibit competitive total phenolic content and robust flavonoid levels, comparable to many Mediterranean EVOOs. The principal distinction lies in the shift from complex secoiridoids toward simpler phenols, particularly hydroxytyrosol, reflecting advanced phenolic transformation during storage. These trends are fully consistent with published evidence showing that cultivar, processing conditions, and storage environment shape the final phenolic profile of EVOOs, often outweighing geographic origin alone (Ben Mansour et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Castillo-Luna \u0026amp; Priego-Capote, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Korkmaz, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Korkmaz et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2025\u003c/span\u003e; Kritikou et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Negro et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eWith regard to the increasing role of olive oil in culinary practices, along with the rise of cultivation and production of olive oil in Oman in recent years, we have attempted to analyze EVOOs in the Omani market. For this, six various brands, including international brands and two locally manufactured kinds, were analyzed for the phenolic profile and compared to previously assessed EVOOs. The findings demonstrate that the phenolic profile of EVOOs available in the Omani market aligns with the range of Mediterranean EVOOs, confirming that local and imported products maintain competitive phenolic levels despite climatic and storage challenges. The optimized extraction method, reinforced by machine learning-based feature importance analysis, underscores the critical role of solvent polarity and salt addition in maximizing phenolic recovery. Phenolic transformations during storage, notably the increase in hydroxytyrosol and tyrosol alongside the decline of oleocanthal and oleacein, reflect dynamic compositional changes affecting oil bioactivity. These insights emphasize that total phenolic content alone is insufficient to assess EVOO quality; detailed profiling of individual compounds is essential. Overall, this study establishes a valuable baseline for monitoring and improving the phenolic quality of olive oils in Oman, supporting both consumer health and the development of the nascent local olive oil industry.\u003c/p\u003e"},{"header":"Declarations","content":" \u003cp\u003e \u003cstrong\u003eCompeting Interests\u003c/strong\u003e \u003cp\u003eThe authors declare no competing interests\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eAzza A. H. Al Shamli: Methodology, Validation, Investigation, Data curation, Formal analysis, Writing \u0026ndash; first draft, review and editing.Maryam Mousavizadegan: Data analysis and feature importance calculations, Writing - review and editing.Haider A. J. Al Lawati: Supervision, Project administration, Conceptualization, Resources, Writing \u0026ndash; review and editing.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThe authors would like to acknowledge the Ministry of High Education, Research and Innovation for their generous financial support through the RC/RG-SCI/CHEM/22/02.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe datasets generated and analyzed during the current study are available from the corresponding author upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAbdu Hussen A (2022) High-performance liquid chromatography (HPLC): A review. 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Nutr Res Rev 18(1):98\u0026ndash;112. ttps://doi.org/10.1079/NRR200495\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":"food-analytical-methods","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Food Analytical Methods](https://www.springer.com/journal/12161)","snPcode":"12161","submissionUrl":"https://submission.nature.com/new-submission/12161/3","title":"Food Analytical Methods","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Extra virgin olive oil, Phenolic compounds, LC–MS/MS, Salt-assisted extraction, Hydroxytyrosol, Omani market","lastPublishedDoi":"10.21203/rs.3.rs-9117332/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9117332/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study investigates the phenolic composition of extra virgin olive oil (EVOO) from the Omani market and optimizes the phenolic extraction process. The addition of 10% (w/v) sodium chloride to the extraction solvent increased phenolic recovery by 20\u0026ndash;30%. Feature importance analysis identified solvent polarity, influenced by solvent type, salt concentration, and volume, as the key factor driving extraction efficiency. A validated liquid chromatography\u0026ndash;tandem mass spectrometry (LC\u0026ndash;MS/MS) method quantified ten phenolic compounds in six commercial EVOO samples. Acid values ranged from 0.01% to 0.11%, and peroxide values were below 12 meq O₂ kg⁻\u0026sup1;, confirming compliance with EVOO quality standards. Total phenolic content ranged from 116 to 250 mg kg⁻\u0026sup1;. Two locally produced Omani oils exhibited phenolic profiles comparable to high-quality Mediterranean EVOOs. Elevated hydroxytyrosol levels indicate phenolic transformation during storage. This study provides baseline data supporting quality control and nutritional evaluation of EVOOs in the Omani market.\u003c/p\u003e","manuscriptTitle":"Phenolic Profile Characterization of Extra Virgin Olive Oils from the Omani Market Using a Salt-Assisted Extraction and LC-MS/MS Approach","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-17 19:43:15","doi":"10.21203/rs.3.rs-9117332/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-05-09T04:08:50+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-04T10:03:05+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-26T21:52:45+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"337506635620723082783189612905041813352","date":"2026-04-14T05:53:36+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"281028158913982883235461990382477377588","date":"2026-04-12T20:27:28+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"95733570801168410333700589833461321550","date":"2026-04-09T11:39:55+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-04-09T08:32:04+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-03-17T06:36:45+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-03-17T06:36:39+00:00","index":"","fulltext":""},{"type":"submitted","content":"Food Analytical Methods","date":"2026-03-13T17:57:58+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"food-analytical-methods","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Food Analytical Methods](https://www.springer.com/journal/12161)","snPcode":"12161","submissionUrl":"https://submission.nature.com/new-submission/12161/3","title":"Food Analytical Methods","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"07ae241a-7623-4fe8-9812-a8d5b61f2311","owner":[],"postedDate":"April 17th, 2026","published":true,"recentEditorialEvents":[{"type":"decision","content":"Revision requested","date":"2026-05-09T04:08:50+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-04T10:03:05+00:00","index":13,"fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"in-revision","subjectAreas":[],"tags":[],"updatedAt":"2026-05-09T04:24:30+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-17 19:43:15","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9117332","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9117332","identity":"rs-9117332","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}