Optimal melatonin threshold for postharvest quality preservation of guava under ambient storage

Optimal melatonin threshold for postharvest quality preservation of guava under ambient storage | 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 Optimal melatonin threshold for postharvest quality preservation of guava under ambient storage Tanshu Chaudhary, Rashmi Panwar, Pratibha ., Rishabh Raj, Krishna ., and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9449990/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 6 You are reading this latest preprint version Abstract Postharvest losses and rapid quality deterioration under ambient conditions remain major constraints in guava storage and optimal strategies for extending shelf life using naturally occurring plant growth regulator-like molecules are still not well established. This study evaluated the efficacy of postharvest melatonin (MT) application in enhancing shelf life and maintaining the quality of guava cv. Pant Prabhat stored under ambient conditions. Fruits were treated with various MT concentrations (0, 200, 400, 600 and 800 µM) and evaluated over a 15-day storage period. Results demonstrated a significant dose-dependent response, with 600 µM MT emerging as the optimal treatment. This concentration significantly reduced physiological loss in weight (11.34%), shrinkage (12.15%) and decay incidence (46.67%), while maintaining higher ascorbic acid (172.33 mg/100 g), total soluble solids (12.57 °Brix) and titratable acidity compared to the control. In contrast, the 800 µM dose showed reduced effectiveness, suggesting a possible metabolic threshold. Overall, melatonin application at 600 µM effectively delayed senescence and preserved fruit quality, highlighting its potential as a sustainable and non-toxic strategy for improving postharvest management and extending the marketable life of guava. Melatonin postharvest physiology shelf life ambient storage guava Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Introduction Guava ( Psidium guajava L.) is a widely cultivated tropical fruit valued for its high nutritional and economic importance (Kumar et al. 2025 ). India is the leading producer of guava, contributing 5.61 million tonnes from 0.37 million hectares with an average productivity of 15.11 MT ha⁻¹, ranking fourth and fifth among fruit crops in area and production, respectively, after mango, banana, citrus and papaya (MoA&FW, 2025). It is an excellent source of dietary fibre, vitamins and bioactive compounds such as phenolics and flavonoids, which contribute to its strong antioxidant and health promoting properties (Anjum et al. 2020 ). Owing to its superior nutritional and medicinal attributes, guava is often referred to as a “superfruit” and plays a significant role in ensuring nutritional security. Despite its immense nutritional and economic importance, guava is highly perishable in nature due to its climacteric behaviour, high respiration rate and rapid metabolic activity after harvest (Mangaraj et al. 2018 ). These physiological characteristics lead to accelerated ripening, moisture loss, tissue softening and increased susceptibility to microbial decay, ultimately resulting in significant postharvest losses (Fan et al. 2022 ). Under ambient storage conditions, guava fruits exhibit a very short shelf life, typically ranging from 4 to 7 days, which poses a serious constraint in marketing, transportation and export (Francisco et al. 2020 ; Yousaf et al. 2024 ). Furthermore, improper postharvest handling leads to rapid deterioration in physicochemical quality attributes such as firmness, acidity, ascorbic acid content and overall fruit acceptability. In recent years, increasing consumer awareness regarding food safety and environmental sustainability has shifted the focus from synthetic chemical treatments to eco-friendly and biologically safe alternatives for postharvest management (Chen et al. 2019 ; Yan et al. 2019 ; Chaudhary et al. 2026 ). Among these, edible coatings and plant-derived bioactive compounds have emerged as promising approaches to enhance shelf life and maintain fruit quality (Kohli et al. 2024 ; Panwar et al. 2025 ; Raj et al. 2026 ). These treatments function as semi-permeable barriers that regulate gas exchange, reduce transpiration losses, delay ripening and inhibit microbial growth, thereby improving postharvest performance. Among these bioactive approaches, melatonin has recently emerged as a promising postharvest treatment that can be applied either independently or incorporated into coating systems to enhance fruit quality and storage life. Melatonin (N-acetyl-5-methoxytryptamine), a naturally occurring indoleamine molecule, has gained considerable attention in plant science due to its multifunctional role in regulating plant growth, development and stress responses (Dong et al. 2021 ). In postharvest biology, melatonin has been reported to act as a potent antioxidant and signalling molecule that enhances the activity of antioxidant enzymes, reduces reactive oxygen species (ROS) accumulation, stabilizes cellular membranes and delays senescence (Rastegar et al. 2020 ). These effects are associated with the regulation of antioxidant defense systems, suppression of lipid peroxidation and maintenance of membrane integrity. Additionally, melatonin is known to modulate ethylene biosynthesis by regulating key enzymes involved in the ripening process. Exogenous application of melatonin has been shown to effectively retard ripening, maintain firmness, preserve nutritional quality and extend shelf life in various fruits such as mango, strawberry, pear, cherry and jujube (Ma et al. 2021 ). These beneficial effects are largely attributed to its ability to modulate ethylene biosynthesis, suppress oxidative stress and improve cellular integrity. Although several studies have demonstrated the positive effects of melatonin in different fruit crops, its application in guava, particularly under Indian conditions, remains limited, particularly in relation to concentration-dependent responses and their influence on physicochemical and biochemical changes during storage. Moreover, there is a lack of systematic studies focusing on the optimization of melatonin concentrations and their influence on physicochemical and biochemical attributes during storage. In the case of guava cv. Pant Prabhat, which is known for its superior fruit quality and market preference, information regarding postharvest melatonin-based coating strategies is still scarce. This highlighted a clear research gap in understanding the role of melatonin in enhancing shelf life and maintaining fruit quality in this cultivar. Therefore, the present investigation was undertaken to systematically evaluate the efficacy of melatonin-based coatings at different concentrations on physiological, biochemical and quality attributes of guava ( Psidium guajava L.) cv. Pant Prabhat, aiming to establish a robust protocol for maintaining quality under ambient storage conditions. Materials and methods Procurement of fruits and preparation of coating solutions Freshly matured, uniform-sized guava ( Psidium guajava L.) fruits cv. Pant Prabhat were procured from the Horticulture Research Centre, Patharchatta, Pantnagar, Uttarakhand, India. Fruits free from mechanical damage, disease and visible defects were selected for the study. Immediately after harvest, fruits were carefully transported to the laboratory in corrugated boxes to avoid physical injury. Analytical grade melatonin (N-acetyl-5-methoxytryptamine) was procured from Sigma-Aldrich (Sigma-Aldrich, USA) and all other chemicals and reagents used in the experiment were of analytical grade and obtained from CDH Pvt. Ltd. (New Delhi, India). Melatonin solutions of different concentrations (200, 400, 600 and 800 µM) were prepared using distilled water based on molarity calculations. Coating treatment and storage conditions The selected fruits were washed with distilled water, air-dried at room temperature and subjected to coating treatments. Fruits were dipped in respective melatonin solutions for 10 minutes, followed by air drying under ambient laboratory conditions to allow uniform coating formation. Control fruits were kept untreated. After treatment, coated and uncoated fruits were stored under ambient conditions (15–21°C) for further analysis. Observations on various physical and biochemical parameters were recorded at regular intervals (0, 3, 6, 9, 12 and 15 days of storage). However, in certain treatments, fruits became unmarketable due to severe decay and spoilage beyond 12 days and were therefore excluded from further evaluation at 15 days. Experimental design The experiment was conducted in a factorial completely randomized design (FCRD) comprising two factors: (i) treatment, including control (untreated) and melatonin at 200, 400, 600 and 800 µM and (ii) storage duration (0, 3, 6, 9, 12 and 15 days), with three replications. Physical parameters Fully mature fruits were taken for analysis. Fruit weight was recorded using an electronic balance and expressed in grams (g). Fruit length and diameter were measured using digital vernier calipers and expressed in millimetres (mm). Fruit volume was determined by the water displacement method and expressed in millilitres (mL). Physiological loss in weight (PLW) was calculated as the percentage reduction in fruit weight during storage. Shrinkage (%) was estimated based on the reduction in fruit diameter over time and decay incidence was recorded based on the number of fruits showing dark brown or black lesions and expressed as percentage of total fruits (Dhami et al. 2023 ). TSS, pH, acidity, ascorbic and sugar pH was estimated using a pH meter and total soluble solids (TSS) of guava juice were determined using a hand refractometer (Fisher, 0–50 °Brix) following the method of Ranganna ( 1986 ) and the results were expressed as °Brix. Titratable acidity (TA) was determined by titration according to AOAC ( 1980 ) and expressed as % citric acid equivalents. Ascorbic acid content was estimated by the 2,6-dichlorophenol-indophenol titration method (Ranganna, 1986 ). Total reducing and total sugars on fresh weight were determined following AOAC ( 1980 ). Statistical Analysis The experimental data were analysed using analysis of variance (ANOVA) appropriate for a factorial completely randomized design (FCRD), considering treatment, storage duration and their interaction effects, following Snedecor and Cochran ( 1987 ). The significance of differences among treatments was tested at p ≤ 0.05. For multivariate analysis, data were standardized using z-score normalization. Principal Component Analysis (PCA) was performed to identify major sources of variability among treatments. Pearson’s correlation coefficients (r) were computed to assess relationships among physicochemical attributes, with significance tested at p ≤ 0.05 and p ≤ 0.01. Hierarchical cluster analysis (HCA) was conducted using Euclidean distance and Ward’s method to classify treatments based on similarity. Radar plots were used for integrated visualization of quality and deterioration-related attributes. Results Physiological loss in weight (PLW) and fruit weight A significant effect (p ≤ 0.05) of melatonin treatments, storage duration and their interaction (T × D) was observed on physiological loss in weight (PLW) and fruit weight (Fig. 1 ). PLW increased progressively during storage, reaching 24.06% at 15 days, with control fruits (T₁) exhibiting the highest loss (31.52%), whereas T₄ (600 µM melatonin) consistently recorded the lowest values (11.34%), followed by T₃ (400 µM; 18.11%). In parallel, fruit weight declined significantly, with T₄ maintaining the highest retention (130.00 g) compared to control (99.33 g). This inverse relationship indicated that weight loss was primarily governed by moisture loss through transpiration and respiration. The pronounced reduction in PLW under T₄ suggested enhanced membrane stability and reduced permeability, likely due to melatonin-mediated scavenging of reactive oxygen species (ROS) and suppression of lipid peroxidation (Rastegar et al. 2020 ; Dong et al. 2021 ). Additionally, regulation of ethylene biosynthesis and respiration may have contributed to delayed senescence and reduced metabolic activity (Ma et al. 2021 ). Similar reductions in weight loss have been reported under postharvest treatments that limit desiccation and enhance stress tolerance (Samra et al. 2014 ; Navarro-Tarazaga et al. 2011 ; Oliveira et al. 2018 ). The comparatively lower efficiency at higher concentration (800 µM) further indicated a concentration-dependent response. Fruit volume, length and diameter Fruit volume, length and diameter were significantly (p ≤ 0.05) influenced by melatonin treatments and storage duration (Fig. 2 ), showing a progressive decline during storage. Fruit volume decreased markedly from 126.00 to 84.87 cm³, with control fruits (T₁) exhibiting the most pronounced loss (108.33 to 56.67 cm³), whereas T₄ (600 µM melatonin) maintained substantially higher values (149.00 to 109.67 cm³), followed by T₂ (130.00 to 91.67 cm³). A similar declining pattern was observed in fruit length, which reduced from 58.48 to 46.47 mm, with maximum reduction in control (55.48 to 38.00 mm), while T₄ retained the highest values (61.09 to 53.00 mm). Likewise, fruit diameter decreased from 64.31 to 53.60 mm, with control fruits showing the greatest reduction (61.90 to 48.33 mm), whereas T₄ consistently maintained higher values (67.89 to 59.67 mm). The pronounced reduction in dimensional attributes in control fruits indicated severe loss of cell turgidity and structural collapse during storage, whereas the improved retention under melatonin treatment, particularly at 600 µM, suggested preservation of cellular integrity. This effect could be attributed to reduced transpirational water loss and stabilization of membrane systems, thereby limiting tissue shrinkage. Similar maintenance of fruit size under postharvest treatments has been reported in previous studies (Ma et al. 2021 ). Shrinkage (%) Shrinkage increased significantly (p ≤ 0.05) during storage, with clear variation among treatments (Fig. 3 ). Shrinkage increased progressively during storage across all treatments, with control fruits (T₁) exhibiting the highest value (21.82%) at 15 days, indicating severe loss of cell turgidity and structural collapse. In contrast, melatonin-treated fruits showed significantly lower shrinkage, with T₄ (600 µM) recording the minimum value (12.15%), followed by T₃ (400 µM; 15.50%), whereas T₂ and T₅ exhibited comparatively higher shrinkage. This consistent trend across storage intervals suggested improved maintenance of cellular integrity under melatonin treatment. The reduced shrinkage in T₄ could be attributed to enhanced retention of cellular water status and preservation of cell wall structure, thereby limiting tissue contraction and surface deformation. Melatonin-mediated regulation of transpirational water loss and stabilization of membrane systems likely contributed to maintaining cell turgor and structural stability during storage (Ma et al. 2021 ; Baldwin et al. 1995 ; Bautista-Baños et al. 2006 ). Decay (%) Decay percentage also increased markedly with storage duration, with control fruits showing the highest decay (93.33%) at 15 days, reflecting rapid tissue deterioration and increased susceptibility to microbial infection. In contrast, melatonin treatments significantly suppressed decay, with T₄ (600 µM) recording the lowest value (46.67%), followed by T₃ (53.33%), whereas T₂ and T₅ exhibited substantially higher decay levels. These trends were also evident from visual observations (Figs. 3 & 4 ), where control fruits exhibited severe browning and decay, whereas melatonin-treated fruits (T₄, 600 µM) maintained superior visual quality with minimal deterioration throughout the storage period. The pronounced reduction in decay under melatonin treatment indicated enhanced resistance to pathogen development and delayed senescence. This may be associated with activation of defense-related enzymes such as peroxidase (POD) and phenylalanine ammonia-lyase (PAL), along with increased accumulation of phenolic compounds that strengthen cell walls and inhibit microbial proliferation (Dong et al. 2021 ; Ma et al. 2021 ). Additionally, improved membrane integrity and reduced metabolic activity likely restricted infection progression. Similar reductions in decay have been reported in melatonin-treated fruits, where enhanced antioxidant defense and delayed senescence contributed to extended shelf life (Aghdam and Fard, 2017 ; Gao et al. 2016 ). The comparatively lower efficiency observed at higher concentration (800 µM) further indicated a concentration-dependent response. Overall, 600 µM melatonin consistently demonstrated superior effectiveness in minimizing shrinkage and decay, thereby preserving structural integrity and extending postharvest life. Juice pH, total soluble solids (TSS) and titratable acidity (TA) pH, TSS and TA were significantly influenced (p ≤ 0.05) by melatonin treatments, storage duration and their interaction (T × D) (Fig. 5 ). A progressive increase in pH was observed during storage, with control fruits (T₁) showing a rapid rise (3.81 to 5.27 by day 9), indicating accelerated ripening, whereas melatonin-treated fruits exhibited a more controlled increase, particularly T₄ (600 µM), which maintained comparatively lower values (3.78 to 5.10 at day 15). TSS exhibited a typical climacteric pattern, increasing initially and declining thereafter; control fruits reached an early peak (13.73 °Brix at day 6) followed by a sharp decline, while melatonin-treated fruits, especially T₄, showed a gradual increase with sustained levels (12.57 °Brix at day 15), indicating delayed substrate depletion. In contrast, titratable acidity declined steadily during storage, with control fruits showing a pronounced reduction (0.35 to 0.15%), whereas T₄ retained higher acidity (0.34 to 0.19%), reflecting slower organic acid utilization. The rapid increase in pH and decline in acidity in control fruits indicated accelerated consumption of organic acids through respiration, whereas the moderated changes under melatonin treatment suggest suppression of metabolic activity. The delayed peak and stabilization of TSS further support reduced conversion and utilization of sugars, indicating a slower ripening process. This effect could be attributed to melatonin-mediated regulation of respiration and ethylene biosynthesis, thereby maintaining a more balanced sugar-acid metabolism (Ma et al. 2021 ). Additionally, improved cellular integrity and reduced oxidative stress under melatonin treatment may have contributed to stabilization of biochemical attributes during storage (Dong et al. 2021 ). Similar patterns have been reported in postharvest studies where treatments delayed metabolic turnover, resulting in moderated pH increase, stabilized TSS and improved retention of acidity (Tanada-Palmu et al. 2005; Martinez-Romero et al. 2002 ; Hernandez-Munoz et al. 2008 ). Overall, 600 µM melatonin effectively regulated biochemical changes, indicating its role in delaying ripening and maintaining fruit quality during storage. Ascorbic acid (mg/100 g) Ascorbic acid content was significantly affected (p ≤ 0.05) by melatonin treatments, storage duration and their interaction (T × D) (Fig. 5 ), showing a consistent decline during storage. The reduction was most pronounced in control fruits (T₁), where ascorbic acid decreased sharply from 282.08 to 126.03 mg/100 g by day 12, indicating rapid oxidative degradation. In contrast, melatonin-treated fruits exhibited a slower rate of decline, with T₄ (600 µM) maintaining the highest levels throughout storage (203.79 mg/100 g at day 12 and 172.33 mg/100 g at day 15), followed by T₃ (400 µM), whereas T₂ and T₅ showed comparatively greater losses. This trend indicated enhanced preservation of antioxidant capacity under optimal melatonin concentration. The rapid depletion of ascorbic acid in control fruits reflects increased oxidative stress and higher metabolic turnover during ripening, whereas the moderated decline under melatonin treatment suggested reduced oxidation and improved redox stability. Ascorbic acid is readily oxidized during storage and its retention under melatonin treatment may be associated with suppression of reactive oxygen species and stabilization of antioxidant systems (Rastegar et al. 2020 ). Additionally, reduced respiration and delayed ripening may limit its utilization, thereby maintaining higher levels (Ma et al. 2021 ). Similar retention of ascorbic acid under postharvest treatments has been reported in earlier studies, where reduced oxidative degradation contributed to improved nutritional quality (Ali et al. 2019 ). Sugar content Total, reducing and non-reducing sugars were significantly affected (p ≤ 0.05) by melatonin treatments, storage duration and their interaction (T × D), exhibiting a progressive increase during storage followed by a slight decline at later stages (Fig. 6 ). Control fruits (T₁) showed a rapid accumulation of sugars, with total sugars increasing from 7.66 to 10.23%, reducing sugars reaching 5.18% by day 9 and non-reducing sugars peaking at 5.07% by day 12, followed by a decline, indicating accelerated carbohydrate hydrolysis and early substrate depletion. A similar but less pronounced trend was observed in T₂ and T₅. In contrast, melatonin-treated fruits exhibited a moderated and sustained increase, with T₄ (600 µM) maintaining comparatively stable levels (total sugars: 7.61 to 9.93%; reducing sugars: up to 5.00%; non-reducing sugars: up to 4.93%), followed by T₃, indicating delayed carbohydrate conversion and improved metabolic stability. The initial increase in sugars reflects hydrolysis of complex carbohydrates and conversion of polysaccharides into soluble sugars, whereas the subsequent decline in control fruits suggested rapid utilization of sugars as respiratory substrates. The moderated accumulation under melatonin treatment indicated suppression of metabolic turnover and delayed ripening. This could be attributed to reduced activity of hydrolytic enzymes and regulation of respiration, leading to a more controlled conversion and utilization of carbohydrates. Additionally, melatonin-mediated stabilization of cellular metabolism may contribute to maintaining sugar balance during storage (Ma et al. 2021 ). Similar patterns have been reported where postharvest treatments moderated sugar accumulation and delayed senescence by reducing metabolic intensity (Wills and Rigney, 1979 ; Hoa and Ducamp, 2008 ; Abassi et al. 2011; Nair et al. 2021 ). The comparatively lower stability observed at higher concentration (800 µM) further supports a concentration-dependent response. Overall, 600 µM melatonin effectively regulated sugar metabolism, resulting in sustained sugar levels and delayed ripening during storage. Integrated multivariate analysis of physicochemical attributes Principal component analysis of physicochemical attributes Principal component analysis (PCA) showed that PC1 and PC2 accounted for 76.36% and 19.94% of the total variance, respectively, explaining 96.30% cumulative variability (Fig. 7 ). The PCA score plot revealed a clear separation of treatments along PC1, indicating a strong influence of melatonin on the overall physicochemical profile of guava fruits. Control fruits (T₁) were distinctly positioned away from treated samples, reflecting rapid deterioration, whereas T₄ (600 µM) formed a distinct cluster associated with superior quality retention. The spatial distribution suggested a clear opposition between quality-related attributes and deterioration parameters, where treatments maintaining higher fruit weight, size, sugars and ascorbic acid were separated from those associated with increased physiological loss in weight (PLW), shrinkage and decay. This pattern indicated that melatonin effectively modulated postharvest physiological processes, leading to delayed senescence and improved biochemical stability. Overall, the PCA highlighted a strong treatment-dependent response, with 600 µM melatonin exhibiting the most favourable positioning, confirming its effectiveness in preserving fruit quality during storage. Correlation Analysis of Physicochemical Attributes Pearson’s correlation analysis revealed strong correlations among physicochemical attributes of guava (Fig. 8 ). Quality-related parameters such as ascorbic acid, total sugars, reducing sugars and fruit weight exhibited strong positive correlations with each other (r = 0.73–0.99), indicating their coordinated role in maintaining fruit quality during storage. Similarly, fruit volume, length and diameter were highly positively correlated (r = 0.91–0.98), reflecting their dependence on cellular turgidity and structural integrity. In contrast, physiological loss in weight (PLW), shrinkage and decay showed strong negative correlations with most quality attributes, particularly fruit weight (r = − 0.98), ascorbic acid (r = − 0.96) and sugars (r = − 0.84 to − 0.89), highlighting the inverse relationship between quality retention and postharvest deterioration. Moreover, decay exhibited a strong positive correlation with PLW (r = 0.96) and shrinkage (r = 0.94), indicating that moisture loss and tissue collapse significantly contribute to disease progression. The correlation pattern clearly demonstrated that deterioration processes are closely associated with loss of structural and biochemical integrity, whereas maintenance of antioxidant capacity and carbohydrate status supports overall fruit quality. These findings confirm that effective treatments reducing PLW and oxidative degradation can simultaneously preserve multiple quality attributes. Hierarchical clustering analysis of physicochemical attributes Hierarchical cluster analysis revealed a distinct clustering pattern among treatments based on their physicochemical characteristics (Fig. 9 ). The dendrogram distinctly separated the samples into major clusters, indicating substantial variation in fruit quality as influenced by melatonin treatments and storage duration. Control samples (T₁) were grouped separately and formed a distinct cluster, reflecting their pronounced deterioration and poor quality retention during storage. In contrast, melatonin-treated samples exhibited closer clustering, particularly those treated with 600 µM (T₄), which consistently grouped with samples characterized by superior physicochemical attributes. The proximity of T₄ samples across different storage intervals suggested greater stability and uniformity in maintaining fruit quality. Intermediate clustering was observed for T₃ (400 µM), whereas T₂ (200 µM) and T₅ (800 µM) showed comparatively dispersed grouping, indicating less consistent performance. The clustering pattern corroborates the PCA results, confirming that treatments preserving higher fruit weight, structural integrity and biochemical quality were distinctly separated from those associated with increased PLW, shrinkage and decay. Overall, the dendrogram highlighted a strong treatment-dependent response, with 600 µM melatonin demonstrating the most consistent and favourable clustering pattern, indicative of its effectiveness in maintaining postharvest quality. Integrated physicochemical profiling using radar analysis The overall response of guava fruits to different melatonin treatments across physicochemical attributes is illustrated in Fig. 10 . The radar plot provided an integrated visualization of both quality-related and deterioration-associated parameters, clearly demonstrating treatment-dependent variation during storage. Among the treatments, T₄ (600 µM melatonin) exhibited the most expanded and uniform profile, indicating superior retention of fruit quality. This treatment maintained higher levels of fruit weight, dimensional attributes, sugars and ascorbic acid, while simultaneously showing lower values of physiological loss in weight (PLW), shrinkage and decay. In contrast, control fruits (T₁) displayed a comparatively restricted profile, reflecting reduced quality retention and increased susceptibility to deterioration. Treatments T₃ (400 µM) showed moderate performance, whereas T₂ (200 µM) and T₅ (800 µM) exhibited relatively variable responses, suggesting less effective regulation of physiological and biochemical processes. Overall, the radar-based assessment confirms that melatonin treatment, particularly at 600 µM, effectively maintained physicochemical stability and minimized postharvest deterioration. These findings were consistent with the multivariate analyses, reinforcing the role of melatonin in preserving fruit quality during storage. Conclusion The results demonstrated that post-harvest application of melatonin effectively improved fruit quality and extended the storage period of guava by minimizing moisture loss and decay while maintaining structural integrity. The best response was observed with 600 µM of melatonin, which effectively preserved fruit quality and appearance under ambient storage conditions. However, higher concentration (800 µM) showed comparatively lower efficacy for maintaining overall quality of fruit. These findings highlight the importance of optimizing melatonin concentration for postharvest applications. Overall, melatonin emerged as a promising, eco-friendly and non-toxic approach for postharvest management of guava and its integration with advanced storage and packaging technologies could further enhance its commercial applicability. This study also provided practical implications for commercial postharvest handling and export-oriented supply chains. Future studies should focus on molecular-level mechanisms and integration with packaging technologies. Declarations Conflict of Interest The authors declare that there is no conflict of interest regarding the publication of this manuscript. Ethics Approval The authors confirm that all applicable guidelines and standards for plant research were followed during the course of this study. Author Contribution Conceptualization and experimental design were carried out by TC and RP. Execution of the experiment, data collection, analysis and interpretation were performed by TC. Experimental materials were provided by P and RP. Manuscript preparation and editing were carried out by TC, RR, K, KS, RP and P. All authors read and approved the final manuscript. Acknowledgements The authors gratefully acknowledge the Horticulture Research Centre, Govind Ballabh Pant University of Agriculture and Technology (GBPUAT), Pantnagar, for providing the necessary facilities and support for conducting the experiment. Data Availability The datasets generated and analysed during the current study are available from the corresponding author on reasonable request. References Abbasi, K.S., Anjum, N., Sammi, S., Masud, T. and Ali, S. 2011. Effect of coatings and packaging material on the keeping quality of mangoes ( Mangifera indica L.) stored at low temperature. Pakistan Journal of Nutrition, 10(2): 129–138. Aghdam, M.S. and Fard, J.R. 2017. Melatonin treatment attenuates postharvest decay and maintains nutritional quality of strawberry fruits ( Fragaria × ananassa cv. Selva) by enhancing GABA shunt activity. 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Influence of edible coatings with and without calcium on physico-chemical characteristics of guava ( Psidium guajava L.) cv. Gwalior-27 during storage. International Journal of Current Microbiology and Applied Sciences, 10(2): 1200–1208. Navarro-Tarazaga, M.L., Massa, A. and Gago, M.B.P. 2011. Effect of beeswax content on hydroxypropyl methylcellulose-based edible film properties and postharvest quality of coated plums (cv. Angeleno). Food Science and Technology, 44: 23–34. Oliveira, V.R.L., Santos, F.K.G., Leite, R.H.L., Aroucha, E.M.M. and Silva, K.N.O. 2018. Use of biopolymeric coating hydrophobized with beeswax in postharvest conservation of guavas. Food Chemistry, 259: 55–64. Panwar, R., Chaudhary, T. and Rai, R. (2025). Elevating Himalayan horticulture: Innovative post-harvest and value addition strategies for apricot. Indian Farmers’ Digest, 58(12), 31–35. Raj, R., Singh, A. K., Negi, K., Joshi, D., Tiwari, C., Devrani, N., Tiwari, C., Devrani, N., Kakkar, P., Bora, H. and Chaudhary, T. (2026). Biopolymer-Based Edible Coatings for Maintaining Postharvest Fruit Quality: A Review. Applied Fruit Science, 6 8 (1), 34. Ranganna, S. 1986. Handbook of analysis and quality control for fruits and vegetables. Tata McGraw-Hill Publishing Company Limited, New Delhi. Rastegar, S., Khankahdani, H.H. and Rahimzadeh, M. 2020. Effects of melatonin treatment on the biochemical changes and antioxidant enzyme activity of mango fruit during storage. Scientia Horticulturae, 259: 108835. Samra, N.R., Shalan, A.M. and Eltair, B.T. 2014. Efficacy of different edible coatings in improving ‘Murcott tangor’ fruit quality during chilled and ambient storage. Journal of Plant Production, 5: 1283–1302. Snedecor, G.W. and Cochran, W.G. 1987. Statistical methods. Oxford and IBH Publishing Co., New Delhi. Tanada-Palmu, P.S. and Grosso, C.F. 2005. Effect of edible wheat gluten-based films and coatings on refrigerated strawberry ( Fragaria × ananassa ). Postharvest Biology and Technology, 36(2): 199–208. Wills, R.B.G. and Rigney, C.J. 1979. Effect of calcium on activity of mitochondria and pectic enzymes isolated from tomato fruits. Journal of Food Biochemistry, 3(2): 103–110. Yan, J., Luo, Z. and Ban, Z. 2019. Effect of layer-by-layer edible coating on strawberry quality and metabolites during storage. Postharvest Biology and Technology, 147: 29–38. Yousaf, A.A., Abbasi, K.S., Ibrahim, M.S., Sohail, A., Faiz, M. and Khadim, M. 2024. Storage stability assessment of guava ( Psidium guajava L.) cv. ‘Gola’ in response to different packaging materials. Sustainable Food Technology, 2(1): 210–221. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Reviewers agreed at journal 03 May, 2026 Reviewers agreed at journal 25 Apr, 2026 Reviewers invited by journal 20 Apr, 2026 Editor assigned by journal 18 Apr, 2026 Submission checks completed at journal 18 Apr, 2026 First submitted to journal 17 Apr, 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. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9449990","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":629467391,"identity":"3225aec7-68a8-4bc7-b520-5aea02a9f500","order_by":0,"name":"Tanshu Chaudhary","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA3ElEQVRIiWNgGAWjYJACZgaGA0CKsfEBkOThI6ScB66FjbHZACTARoIWBjYJkAhBLfbsZw9/Lmy7I2c+v7mt8muOnQwbA/PDRzfw2cKTlyY9s+2ZscwxxrbbstuSgQ5jMzbOweuwHDNm3rbDiTPYgFoktzEDtfCwSePVwv/G+DNMS7HktnoitEjkGEjDtDB+3HaYCC033phJ85w7bCzBltgszbjtOA8bMwG/sPfnGH/mKTssJ8F8/OHHn9uq7fnZmx8+xqcFBTDzgElilYMA4w9SVI+CUTAKRsGIAQAlbkAEwuWY5QAAAABJRU5ErkJggg==","orcid":"","institution":"Govind Ballabh Pant University of Agriculture and Technology","correspondingAuthor":true,"prefix":"","firstName":"Tanshu","middleName":"","lastName":"Chaudhary","suffix":""},{"id":629467392,"identity":"863d708d-cbcf-4235-8349-64536df0bb0e","order_by":1,"name":"Rashmi Panwar","email":"","orcid":"","institution":"Govind Ballabh Pant University of Agriculture and Technology","correspondingAuthor":false,"prefix":"","firstName":"Rashmi","middleName":"","lastName":"Panwar","suffix":""},{"id":629467397,"identity":"0463d1b4-3622-4fe2-a138-d75c91d234d0","order_by":2,"name":"Pratibha .","email":"","orcid":"","institution":"Govind Ballabh Pant University of Agriculture and Technology","correspondingAuthor":false,"prefix":"","firstName":"Pratibha","middleName":"","lastName":".","suffix":""},{"id":629467399,"identity":"f8e96117-7e9f-4268-bfee-4f34b96c820b","order_by":3,"name":"Rishabh Raj","email":"","orcid":"","institution":"Govind Ballabh Pant University of Agriculture and Technology","correspondingAuthor":false,"prefix":"","firstName":"Rishabh","middleName":"","lastName":"Raj","suffix":""},{"id":629467402,"identity":"c65d4db1-69a6-424a-8935-f91bc8bb9317","order_by":4,"name":"Krishna .","email":"","orcid":"","institution":"Govind Ballabh Pant University of Agriculture and Technology","correspondingAuthor":false,"prefix":"","firstName":"Krishna","middleName":"","lastName":".","suffix":""},{"id":629467404,"identity":"bc4b7429-79b2-4876-94be-7146e4d615df","order_by":5,"name":"Kirtika Sharma","email":"","orcid":"","institution":"Govind Ballabh Pant University of Agriculture and Technology","correspondingAuthor":false,"prefix":"","firstName":"Kirtika","middleName":"","lastName":"Sharma","suffix":""}],"badges":[],"createdAt":"2026-04-17 13:55:33","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9449990/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9449990/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":108000314,"identity":"a043402e-e0cf-46be-a481-c6c670411437","added_by":"auto","created_at":"2026-04-28 11:53:35","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":103105,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of melatonin treatments on physiological loss in weight (PLW) and fruit weight of guava during 15 days of ambient storage. Different letters indicate significant differences at p ≤ 0.05.\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-9449990/v1/d95ed5b9c891f4126f984d58.png"},{"id":108007498,"identity":"696fb97c-8bc4-4c89-83f9-9b1e4c7f2ee0","added_by":"auto","created_at":"2026-04-28 13:00:15","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":91310,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of melatonin treatments on fruit volume, length and diameter of guava during ambient storage. Values represent mean ± SE; different letters indicate significant differences (p ≤ 0.05)\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-9449990/v1/5255f610c3d49d84011c209a.png"},{"id":108000470,"identity":"c38bae47-97f9-4b15-ba82-62e8578e8d9a","added_by":"auto","created_at":"2026-04-28 11:54:10","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":100307,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of melatonin treatments on shrinkage and decay (%) of guava during ambient storage. Means with different letters differ significantly at p ≤ 0.05.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-9449990/v1/77ee84e02f47e5fbea120315.png"},{"id":108000404,"identity":"401580fc-af82-4b4e-a189-2e8e5584dfc2","added_by":"auto","created_at":"2026-04-28 11:53:55","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":744663,"visible":true,"origin":"","legend":"\u003cp\u003eVisual changes in guava fruits under different treatments during ambient storage (0, 3, 6, 9, 12 and 15 days). Control fruits exhibited rapid deterioration, whereas T₄ (600 µM melatonin) maintained better quality and reduced decay.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-9449990/v1/9dd8cb4fe27b22dc9e04bdcf.png"},{"id":108000506,"identity":"48eab8b0-4953-4b28-8512-28db2e146206","added_by":"auto","created_at":"2026-04-28 11:54:16","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":158229,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of melatonin treatments on pH, TSS, titratable acidity and ascorbic acid of guava during storage. Different letters indicate significant differences (p ≤ 0.05).\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-9449990/v1/bddb16cc7a781ea24237b20c.png"},{"id":108000500,"identity":"d2cba2eb-9110-4432-9dca-9aeaf495ed1e","added_by":"auto","created_at":"2026-04-28 11:54:15","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":97817,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of melatonin treatments on total, reducing and non-reducing sugars of guava during storage. Values are mean ± SE; different letters indicate significant differences (p ≤ 0.05).\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-9449990/v1/101d017924e600a8defcf57b.png"},{"id":108000322,"identity":"c7c8795c-76c2-4d0a-bca9-c02f73d6e35e","added_by":"auto","created_at":"2026-04-28 11:53:41","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":43645,"visible":true,"origin":"","legend":"\u003cp\u003ePrincipal component analysis (PCA) score plot showing treatment distribution based on physicochemical attributes of guava.\u003c/p\u003e","description":"","filename":"image7.png","url":"https://assets-eu.researchsquare.com/files/rs-9449990/v1/6667e83ebd1e63fa4ab4da91.png"},{"id":108000605,"identity":"75e4f1e1-0565-4ce2-a5e9-9303df063b5a","added_by":"auto","created_at":"2026-04-28 11:54:44","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":191495,"visible":true,"origin":"","legend":"\u003cp\u003ePearson correlation heatmap showing relationships among physicochemical attributes of guava under melatonin treatments.\u003c/p\u003e","description":"","filename":"image8.png","url":"https://assets-eu.researchsquare.com/files/rs-9449990/v1/5508b450de961a0639f0f71c.png"},{"id":108000472,"identity":"35118740-e72d-4c8f-92ae-afb2a9b24ce7","added_by":"auto","created_at":"2026-04-28 11:54:11","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":26516,"visible":true,"origin":"","legend":"\u003cp\u003eHierarchical clustering dendrogram illustrating grouping of treatments based on physicochemical attributes.\u003c/p\u003e","description":"","filename":"image9.png","url":"https://assets-eu.researchsquare.com/files/rs-9449990/v1/75e407d16958dd39fa315edc.png"},{"id":108000323,"identity":"94967c5e-9a0f-4a30-a344-3b7f772d50d6","added_by":"auto","created_at":"2026-04-28 11:53:41","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":108357,"visible":true,"origin":"","legend":"\u003cp\u003eRadar plot showing integrated physicochemical profiling of guava under different melatonin treatments.\u003c/p\u003e","description":"","filename":"image10.png","url":"https://assets-eu.researchsquare.com/files/rs-9449990/v1/28c395340bc88be2595f82c4.png"},{"id":108008939,"identity":"781f61cb-7c96-4bb5-8066-e5acc035fbbe","added_by":"auto","created_at":"2026-04-28 13:08:42","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1938262,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9449990/v1/afdffccf-46aa-4b08-a909-d04f94085592.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Optimal melatonin threshold for postharvest quality preservation of guava under ambient storage","fulltext":[{"header":"Introduction","content":"\u003cp\u003eGuava (\u003cem\u003ePsidium guajava\u003c/em\u003e L.) is a widely cultivated tropical fruit valued for its high nutritional and economic importance (Kumar et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). India is the leading producer of guava, contributing 5.61\u0026nbsp;million tonnes from 0.37\u0026nbsp;million hectares with an average productivity of 15.11 MT ha⁻\u0026sup1;, ranking fourth and fifth among fruit crops in area and production, respectively, after mango, banana, citrus and papaya (MoA\u0026amp;FW, 2025). It is an excellent source of dietary fibre, vitamins and bioactive compounds such as phenolics and flavonoids, which contribute to its strong antioxidant and health promoting properties (Anjum et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Owing to its superior nutritional and medicinal attributes, guava is often referred to as a \u0026ldquo;superfruit\u0026rdquo; and plays a significant role in ensuring nutritional security. Despite its immense nutritional and economic importance, guava is highly perishable in nature due to its climacteric behaviour, high respiration rate and rapid metabolic activity after harvest (Mangaraj et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). These physiological characteristics lead to accelerated ripening, moisture loss, tissue softening and increased susceptibility to microbial decay, ultimately resulting in significant postharvest losses (Fan et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Under ambient storage conditions, guava fruits exhibit a very short shelf life, typically ranging from 4 to 7 days, which poses a serious constraint in marketing, transportation and export (Francisco et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Yousaf et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Furthermore, improper postharvest handling leads to rapid deterioration in physicochemical quality attributes such as firmness, acidity, ascorbic acid content and overall fruit acceptability.\u003c/p\u003e \u003cp\u003eIn recent years, increasing consumer awareness regarding food safety and environmental sustainability has shifted the focus from synthetic chemical treatments to eco-friendly and biologically safe alternatives for postharvest management (Chen et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Yan et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Chaudhary et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2026\u003c/span\u003e). Among these, edible coatings and plant-derived bioactive compounds have emerged as promising approaches to enhance shelf life and maintain fruit quality (Kohli et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Panwar et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2025\u003c/span\u003e; Raj et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2026\u003c/span\u003e). These treatments function as semi-permeable barriers that regulate gas exchange, reduce transpiration losses, delay ripening and inhibit microbial growth, thereby improving postharvest performance. Among these bioactive approaches, melatonin has recently emerged as a promising postharvest treatment that can be applied either independently or incorporated into coating systems to enhance fruit quality and storage life.\u003c/p\u003e \u003cp\u003eMelatonin (N-acetyl-5-methoxytryptamine), a naturally occurring indoleamine molecule, has gained considerable attention in plant science due to its multifunctional role in regulating plant growth, development and stress responses (Dong et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). In postharvest biology, melatonin has been reported to act as a potent antioxidant and signalling molecule that enhances the activity of antioxidant enzymes, reduces reactive oxygen species (ROS) accumulation, stabilizes cellular membranes and delays senescence (Rastegar et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). These effects are associated with the regulation of antioxidant defense systems, suppression of lipid peroxidation and maintenance of membrane integrity. Additionally, melatonin is known to modulate ethylene biosynthesis by regulating key enzymes involved in the ripening process. Exogenous application of melatonin has been shown to effectively retard ripening, maintain firmness, preserve nutritional quality and extend shelf life in various fruits such as mango, strawberry, pear, cherry and jujube (Ma et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). These beneficial effects are largely attributed to its ability to modulate ethylene biosynthesis, suppress oxidative stress and improve cellular integrity.\u003c/p\u003e \u003cp\u003eAlthough several studies have demonstrated the positive effects of melatonin in different fruit crops, its application in guava, particularly under Indian conditions, remains limited, particularly in relation to concentration-dependent responses and their influence on physicochemical and biochemical changes during storage. Moreover, there is a lack of systematic studies focusing on the optimization of melatonin concentrations and their influence on physicochemical and biochemical attributes during storage. In the case of guava cv. Pant Prabhat, which is known for its superior fruit quality and market preference, information regarding postharvest melatonin-based coating strategies is still scarce. This highlighted a clear research gap in understanding the role of melatonin in enhancing shelf life and maintaining fruit quality in this cultivar. Therefore, the present investigation was undertaken to systematically evaluate the efficacy of melatonin-based coatings at different concentrations on physiological, biochemical and quality attributes of guava (\u003cem\u003ePsidium guajava\u003c/em\u003e L.) cv. Pant Prabhat, aiming to establish a robust protocol for maintaining quality under ambient storage conditions.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eProcurement of fruits and preparation of coating solutions\u003c/h2\u003e \u003cp\u003eFreshly matured, uniform-sized guava (\u003cem\u003ePsidium guajava\u003c/em\u003e L.) fruits cv. Pant Prabhat were procured from the Horticulture Research Centre, Patharchatta, Pantnagar, Uttarakhand, India. Fruits free from mechanical damage, disease and visible defects were selected for the study. Immediately after harvest, fruits were carefully transported to the laboratory in corrugated boxes to avoid physical injury. Analytical grade melatonin (N-acetyl-5-methoxytryptamine) was procured from Sigma-Aldrich (Sigma-Aldrich, USA) and all other chemicals and reagents used in the experiment were of analytical grade and obtained from CDH Pvt. Ltd. (New Delhi, India). Melatonin solutions of different concentrations (200, 400, 600 and 800 \u0026micro;M) were prepared using distilled water based on molarity calculations.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eCoating treatment and storage conditions\u003c/h3\u003e\n\u003cp\u003eThe selected fruits were washed with distilled water, air-dried at room temperature and subjected to coating treatments. Fruits were dipped in respective melatonin solutions for 10 minutes, followed by air drying under ambient laboratory conditions to allow uniform coating formation. Control fruits were kept untreated. After treatment, coated and uncoated fruits were stored under ambient conditions (15\u0026ndash;21\u0026deg;C) for further analysis. Observations on various physical and biochemical parameters were recorded at regular intervals (0, 3, 6, 9, 12 and 15 days of storage). However, in certain treatments, fruits became unmarketable due to severe decay and spoilage beyond 12 days and were therefore excluded from further evaluation at 15 days.\u003c/p\u003e\n\u003ch3\u003eExperimental design\u003c/h3\u003e\n\u003cp\u003eThe experiment was conducted in a factorial completely randomized design (FCRD) comprising two factors: (i) treatment, including control (untreated) and melatonin at 200, 400, 600 and 800 \u0026micro;M and (ii) storage duration (0, 3, 6, 9, 12 and 15 days), with three replications.\u003c/p\u003e\n\u003ch3\u003ePhysical parameters\u003c/h3\u003e\n\u003cp\u003eFully mature fruits were taken for analysis. Fruit weight was recorded using an electronic balance and expressed in grams (g). Fruit length and diameter were measured using digital vernier calipers and expressed in millimetres (mm). Fruit volume was determined by the water displacement method and expressed in millilitres (mL). Physiological loss in weight (PLW) was calculated as the percentage reduction in fruit weight during storage. Shrinkage (%) was estimated based on the reduction in fruit diameter over time and decay incidence was recorded based on the number of fruits showing dark brown or black lesions and expressed as percentage of total fruits (Dhami et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e\n\u003ch3\u003eTSS, pH, acidity, ascorbic and sugar\u003c/h3\u003e\n\u003cp\u003epH was estimated using a pH meter and total soluble solids (TSS) of guava juice were determined using a hand refractometer (Fisher, 0\u0026ndash;50 \u0026deg;Brix) following the method of Ranganna (\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e1986\u003c/span\u003e) and the results were expressed as \u0026deg;Brix. Titratable acidity (TA) was determined by titration according to AOAC (\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e1980\u003c/span\u003e) and expressed as % citric acid equivalents. Ascorbic acid content was estimated by the 2,6-dichlorophenol-indophenol titration method (Ranganna, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e1986\u003c/span\u003e). Total reducing and total sugars on fresh weight were determined following AOAC (\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e1980\u003c/span\u003e).\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eStatistical Analysis\u003c/h2\u003e \u003cp\u003eThe experimental data were analysed using analysis of variance (ANOVA) appropriate for a factorial completely randomized design (FCRD), considering treatment, storage duration and their interaction effects, following Snedecor and Cochran (\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e1987\u003c/span\u003e). The significance of differences among treatments was tested at p\u0026thinsp;\u0026le;\u0026thinsp;0.05. For multivariate analysis, data were standardized using z-score normalization. Principal Component Analysis (PCA) was performed to identify major sources of variability among treatments. Pearson\u0026rsquo;s correlation coefficients (r) were computed to assess relationships among physicochemical attributes, with significance tested at p\u0026thinsp;\u0026le;\u0026thinsp;0.05 and p\u0026thinsp;\u0026le;\u0026thinsp;0.01. Hierarchical cluster analysis (HCA) was conducted using Euclidean distance and Ward\u0026rsquo;s method to classify treatments based on similarity. Radar plots were used for integrated visualization of quality and deterioration-related attributes.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003ePhysiological loss in weight (PLW) and fruit weight\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eA significant effect (p\u0026thinsp;\u0026le;\u0026thinsp;0.05) of melatonin treatments, storage duration and their interaction (T \u0026times; D) was observed on physiological loss in weight (PLW) and fruit weight (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). PLW increased progressively during storage, reaching 24.06% at 15 days, with control fruits (T₁) exhibiting the highest loss (31.52%), whereas T₄ (600 \u0026micro;M melatonin) consistently recorded the lowest values (11.34%), followed by T₃ (400 \u0026micro;M; 18.11%). In parallel, fruit weight declined significantly, with T₄ maintaining the highest retention (130.00 g) compared to control (99.33 g). This inverse relationship indicated that weight loss was primarily governed by moisture loss through transpiration and respiration. The pronounced reduction in PLW under T₄ suggested enhanced membrane stability and reduced permeability, likely due to melatonin-mediated scavenging of reactive oxygen species (ROS) and suppression of lipid peroxidation (Rastegar et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Dong et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Additionally, regulation of ethylene biosynthesis and respiration may have contributed to delayed senescence and reduced metabolic activity (Ma et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Similar reductions in weight loss have been reported under postharvest treatments that limit desiccation and enhance stress tolerance (Samra et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Navarro-Tarazaga et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Oliveira et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). The comparatively lower efficiency at higher concentration (800 \u0026micro;M) further indicated a concentration-dependent response.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eFruit volume, length and diameter\u003c/h2\u003e \u003cp\u003eFruit volume, length and diameter were significantly (p\u0026thinsp;\u0026le;\u0026thinsp;0.05) influenced by melatonin treatments and storage duration (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), showing a progressive decline during storage. Fruit volume decreased markedly from 126.00 to 84.87 cm\u0026sup3;, with control fruits (T₁) exhibiting the most pronounced loss (108.33 to 56.67 cm\u0026sup3;), whereas T₄ (600 \u0026micro;M melatonin) maintained substantially higher values (149.00 to 109.67 cm\u0026sup3;), followed by T₂ (130.00 to 91.67 cm\u0026sup3;). A similar declining pattern was observed in fruit length, which reduced from 58.48 to 46.47 mm, with maximum reduction in control (55.48 to 38.00 mm), while T₄ retained the highest values (61.09 to 53.00 mm). Likewise, fruit diameter decreased from 64.31 to 53.60 mm, with control fruits showing the greatest reduction (61.90 to 48.33 mm), whereas T₄ consistently maintained higher values (67.89 to 59.67 mm). The pronounced reduction in dimensional attributes in control fruits indicated severe loss of cell turgidity and structural collapse during storage, whereas the improved retention under melatonin treatment, particularly at 600 \u0026micro;M, suggested preservation of cellular integrity. This effect could be attributed to reduced transpirational water loss and stabilization of membrane systems, thereby limiting tissue shrinkage. Similar maintenance of fruit size under postharvest treatments has been reported in previous studies (Ma et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eShrinkage (%)\u003c/h2\u003e \u003cp\u003eShrinkage increased significantly (p\u0026thinsp;\u0026le;\u0026thinsp;0.05) during storage, with clear variation among treatments (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Shrinkage increased progressively during storage across all treatments, with control fruits (T₁) exhibiting the highest value (21.82%) at 15 days, indicating severe loss of cell turgidity and structural collapse. In contrast, melatonin-treated fruits showed significantly lower shrinkage, with T₄ (600 \u0026micro;M) recording the minimum value (12.15%), followed by T₃ (400 \u0026micro;M; 15.50%), whereas T₂ and T₅ exhibited comparatively higher shrinkage. This consistent trend across storage intervals suggested improved maintenance of cellular integrity under melatonin treatment. The reduced shrinkage in T₄ could be attributed to enhanced retention of cellular water status and preservation of cell wall structure, thereby limiting tissue contraction and surface deformation. Melatonin-mediated regulation of transpirational water loss and stabilization of membrane systems likely contributed to maintaining cell turgor and structural stability during storage (Ma et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Baldwin et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e1995\u003c/span\u003e; Bautista-Ba\u0026ntilde;os et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2006\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eDecay (%)\u003c/h2\u003e \u003cp\u003eDecay percentage also increased markedly with storage duration, with control fruits showing the highest decay (93.33%) at 15 days, reflecting rapid tissue deterioration and increased susceptibility to microbial infection. In contrast, melatonin treatments significantly suppressed decay, with T₄ (600 \u0026micro;M) recording the lowest value (46.67%), followed by T₃ (53.33%), whereas T₂ and T₅ exhibited substantially higher decay levels. These trends were also evident from visual observations (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e \u0026amp; \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e), where control fruits exhibited severe browning and decay, whereas melatonin-treated fruits (T₄, 600 \u0026micro;M) maintained superior visual quality with minimal deterioration throughout the storage period. The pronounced reduction in decay under melatonin treatment indicated enhanced resistance to pathogen development and delayed senescence. This may be associated with activation of defense-related enzymes such as peroxidase (POD) and phenylalanine ammonia-lyase (PAL), along with increased accumulation of phenolic compounds that strengthen cell walls and inhibit microbial proliferation (Dong et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Ma et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Additionally, improved membrane integrity and reduced metabolic activity likely restricted infection progression. Similar reductions in decay have been reported in melatonin-treated fruits, where enhanced antioxidant defense and delayed senescence contributed to extended shelf life (Aghdam and Fard, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Gao et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). The comparatively lower efficiency observed at higher concentration (800 \u0026micro;M) further indicated a concentration-dependent response. Overall, 600 \u0026micro;M melatonin consistently demonstrated superior effectiveness in minimizing shrinkage and decay, thereby preserving structural integrity and extending postharvest life.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eJuice pH, total soluble solids (TSS) and titratable acidity (TA)\u003c/h2\u003e \u003cp\u003epH, TSS and TA were significantly influenced (p\u0026thinsp;\u0026le;\u0026thinsp;0.05) by melatonin treatments, storage duration and their interaction (T \u0026times; D) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). A progressive increase in pH was observed during storage, with control fruits (T₁) showing a rapid rise (3.81 to 5.27 by day 9), indicating accelerated ripening, whereas melatonin-treated fruits exhibited a more controlled increase, particularly T₄ (600 \u0026micro;M), which maintained comparatively lower values (3.78 to 5.10 at day 15). TSS exhibited a typical climacteric pattern, increasing initially and declining thereafter; control fruits reached an early peak (13.73 \u0026deg;Brix at day 6) followed by a sharp decline, while melatonin-treated fruits, especially T₄, showed a gradual increase with sustained levels (12.57 \u0026deg;Brix at day 15), indicating delayed substrate depletion. In contrast, titratable acidity declined steadily during storage, with control fruits showing a pronounced reduction (0.35 to 0.15%), whereas T₄ retained higher acidity (0.34 to 0.19%), reflecting slower organic acid utilization. The rapid increase in pH and decline in acidity in control fruits indicated accelerated consumption of organic acids through respiration, whereas the moderated changes under melatonin treatment suggest suppression of metabolic activity. The delayed peak and stabilization of TSS further support reduced conversion and utilization of sugars, indicating a slower ripening process. This effect could be attributed to melatonin-mediated regulation of respiration and ethylene biosynthesis, thereby maintaining a more balanced sugar-acid metabolism (Ma et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Additionally, improved cellular integrity and reduced oxidative stress under melatonin treatment may have contributed to stabilization of biochemical attributes during storage (Dong et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Similar patterns have been reported in postharvest studies where treatments delayed metabolic turnover, resulting in moderated pH increase, stabilized TSS and improved retention of acidity (Tanada-Palmu et al. 2005; Martinez-Romero et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2002\u003c/span\u003e; Hernandez-Munoz et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). Overall, 600 \u0026micro;M melatonin effectively regulated biochemical changes, indicating its role in delaying ripening and maintaining fruit quality during storage.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eAscorbic acid (mg/100 g)\u003c/h2\u003e \u003cp\u003eAscorbic acid content was significantly affected (p\u0026thinsp;\u0026le;\u0026thinsp;0.05) by melatonin treatments, storage duration and their interaction (T \u0026times; D) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e), showing a consistent decline during storage. The reduction was most pronounced in control fruits (T₁), where ascorbic acid decreased sharply from 282.08 to 126.03 mg/100 g by day 12, indicating rapid oxidative degradation. In contrast, melatonin-treated fruits exhibited a slower rate of decline, with T₄ (600 \u0026micro;M) maintaining the highest levels throughout storage (203.79 mg/100 g at day 12 and 172.33 mg/100 g at day 15), followed by T₃ (400 \u0026micro;M), whereas T₂ and T₅ showed comparatively greater losses. This trend indicated enhanced preservation of antioxidant capacity under optimal melatonin concentration. The rapid depletion of ascorbic acid in control fruits reflects increased oxidative stress and higher metabolic turnover during ripening, whereas the moderated decline under melatonin treatment suggested reduced oxidation and improved redox stability. Ascorbic acid is readily oxidized during storage and its retention under melatonin treatment may be associated with suppression of reactive oxygen species and stabilization of antioxidant systems (Rastegar et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Additionally, reduced respiration and delayed ripening may limit its utilization, thereby maintaining higher levels (Ma et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Similar retention of ascorbic acid under postharvest treatments has been reported in earlier studies, where reduced oxidative degradation contributed to improved nutritional quality (Ali et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eSugar content\u003c/h2\u003e \u003cp\u003eTotal, reducing and non-reducing sugars were significantly affected (p\u0026thinsp;\u0026le;\u0026thinsp;0.05) by melatonin treatments, storage duration and their interaction (T \u0026times; D), exhibiting a progressive increase during storage followed by a slight decline at later stages (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). Control fruits (T₁) showed a rapid accumulation of sugars, with total sugars increasing from 7.66 to 10.23%, reducing sugars reaching 5.18% by day 9 and non-reducing sugars peaking at 5.07% by day 12, followed by a decline, indicating accelerated carbohydrate hydrolysis and early substrate depletion. A similar but less pronounced trend was observed in T₂ and T₅. In contrast, melatonin-treated fruits exhibited a moderated and sustained increase, with T₄ (600 \u0026micro;M) maintaining comparatively stable levels (total sugars: 7.61 to 9.93%; reducing sugars: up to 5.00%; non-reducing sugars: up to 4.93%), followed by T₃, indicating delayed carbohydrate conversion and improved metabolic stability. The initial increase in sugars reflects hydrolysis of complex carbohydrates and conversion of polysaccharides into soluble sugars, whereas the subsequent decline in control fruits suggested rapid utilization of sugars as respiratory substrates. The moderated accumulation under melatonin treatment indicated suppression of metabolic turnover and delayed ripening. This could be attributed to reduced activity of hydrolytic enzymes and regulation of respiration, leading to a more controlled conversion and utilization of carbohydrates. Additionally, melatonin-mediated stabilization of cellular metabolism may contribute to maintaining sugar balance during storage (Ma et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Similar patterns have been reported where postharvest treatments moderated sugar accumulation and delayed senescence by reducing metabolic intensity (Wills and Rigney, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e1979\u003c/span\u003e; Hoa and Ducamp, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Abassi et al. 2011; Nair et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). The comparatively lower stability observed at higher concentration (800 \u0026micro;M) further supports a concentration-dependent response. Overall, 600 \u0026micro;M melatonin effectively regulated sugar metabolism, resulting in sustained sugar levels and delayed ripening during storage.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003eIntegrated multivariate analysis of physicochemical attributes\u003c/h2\u003e \u003cdiv id=\"Sec18\" class=\"Section3\"\u003e \u003ch2\u003ePrincipal component analysis of physicochemical attributes\u003c/h2\u003e \u003cp\u003ePrincipal component analysis (PCA) showed that PC1 and PC2 accounted for 76.36% and 19.94% of the total variance, respectively, explaining 96.30% cumulative variability (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e). The PCA score plot revealed a clear separation of treatments along PC1, indicating a strong influence of melatonin on the overall physicochemical profile of guava fruits. Control fruits (T₁) were distinctly positioned away from treated samples, reflecting rapid deterioration, whereas T₄ (600 \u0026micro;M) formed a distinct cluster associated with superior quality retention. The spatial distribution suggested a clear opposition between quality-related attributes and deterioration parameters, where treatments maintaining higher fruit weight, size, sugars and ascorbic acid were separated from those associated with increased physiological loss in weight (PLW), shrinkage and decay. This pattern indicated that melatonin effectively modulated postharvest physiological processes, leading to delayed senescence and improved biochemical stability. Overall, the PCA highlighted a strong treatment-dependent response, with 600 \u0026micro;M melatonin exhibiting the most favourable positioning, confirming its effectiveness in preserving fruit quality during storage.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003eCorrelation Analysis of Physicochemical Attributes\u003c/h2\u003e \u003cp\u003ePearson\u0026rsquo;s correlation analysis revealed strong correlations among physicochemical attributes of guava (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e). Quality-related parameters such as ascorbic acid, total sugars, reducing sugars and fruit weight exhibited strong positive correlations with each other (r\u0026thinsp;=\u0026thinsp;0.73\u0026ndash;0.99), indicating their coordinated role in maintaining fruit quality during storage. Similarly, fruit volume, length and diameter were highly positively correlated (r\u0026thinsp;=\u0026thinsp;0.91\u0026ndash;0.98), reflecting their dependence on cellular turgidity and structural integrity. In contrast, physiological loss in weight (PLW), shrinkage and decay showed strong negative correlations with most quality attributes, particularly fruit weight (r\u0026thinsp;=\u0026thinsp;\u0026minus;\u0026thinsp;0.98), ascorbic acid (r\u0026thinsp;=\u0026thinsp;\u0026minus;\u0026thinsp;0.96) and sugars (r\u0026thinsp;=\u0026thinsp;\u0026minus;\u0026thinsp;0.84 to \u0026minus;\u0026thinsp;0.89), highlighting the inverse relationship between quality retention and postharvest deterioration. Moreover, decay exhibited a strong positive correlation with PLW (r\u0026thinsp;=\u0026thinsp;0.96) and shrinkage (r\u0026thinsp;=\u0026thinsp;0.94), indicating that moisture loss and tissue collapse significantly contribute to disease progression. The correlation pattern clearly demonstrated that deterioration processes are closely associated with loss of structural and biochemical integrity, whereas maintenance of antioxidant capacity and carbohydrate status supports overall fruit quality. These findings confirm that effective treatments reducing PLW and oxidative degradation can simultaneously preserve multiple quality attributes.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003eHierarchical clustering analysis of physicochemical attributes\u003c/h2\u003e \u003cp\u003eHierarchical cluster analysis revealed a distinct clustering pattern among treatments based on their physicochemical characteristics (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e). The dendrogram distinctly separated the samples into major clusters, indicating substantial variation in fruit quality as influenced by melatonin treatments and storage duration. Control samples (T₁) were grouped separately and formed a distinct cluster, reflecting their pronounced deterioration and poor quality retention during storage. In contrast, melatonin-treated samples exhibited closer clustering, particularly those treated with 600 \u0026micro;M (T₄), which consistently grouped with samples characterized by superior physicochemical attributes. The proximity of T₄ samples across different storage intervals suggested greater stability and uniformity in maintaining fruit quality. Intermediate clustering was observed for T₃ (400 \u0026micro;M), whereas T₂ (200 \u0026micro;M) and T₅ (800 \u0026micro;M) showed comparatively dispersed grouping, indicating less consistent performance. The clustering pattern corroborates the PCA results, confirming that treatments preserving higher fruit weight, structural integrity and biochemical quality were distinctly separated from those associated with increased PLW, shrinkage and decay. Overall, the dendrogram highlighted a strong treatment-dependent response, with 600 \u0026micro;M melatonin demonstrating the most consistent and favourable clustering pattern, indicative of its effectiveness in maintaining postharvest quality.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003eIntegrated physicochemical profiling using radar analysis\u003c/h2\u003e \u003cp\u003eThe overall response of guava fruits to different melatonin treatments across physicochemical attributes is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e. The radar plot provided an integrated visualization of both quality-related and deterioration-associated parameters, clearly demonstrating treatment-dependent variation during storage. Among the treatments, T₄ (600 \u0026micro;M melatonin) exhibited the most expanded and uniform profile, indicating superior retention of fruit quality. This treatment maintained higher levels of fruit weight, dimensional attributes, sugars and ascorbic acid, while simultaneously showing lower values of physiological loss in weight (PLW), shrinkage and decay. In contrast, control fruits (T₁) displayed a comparatively restricted profile, reflecting reduced quality retention and increased susceptibility to deterioration. Treatments T₃ (400 \u0026micro;M) showed moderate performance, whereas T₂ (200 \u0026micro;M) and T₅ (800 \u0026micro;M) exhibited relatively variable responses, suggesting less effective regulation of physiological and biochemical processes. Overall, the radar-based assessment confirms that melatonin treatment, particularly at 600 \u0026micro;M, effectively maintained physicochemical stability and minimized postharvest deterioration. These findings were consistent with the multivariate analyses, reinforcing the role of melatonin in preserving fruit quality during storage.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThe results demonstrated that post-harvest application of melatonin effectively improved fruit quality and extended the storage period of guava by minimizing moisture loss and decay while maintaining structural integrity. The best response was observed with 600 \u0026micro;M of melatonin, which effectively preserved fruit quality and appearance under ambient storage conditions. However, higher concentration (800 \u0026micro;M) showed comparatively lower efficacy for maintaining overall quality of fruit. These findings highlight the importance of optimizing melatonin concentration for postharvest applications. Overall, melatonin emerged as a promising, eco-friendly and non-toxic approach for postharvest management of guava and its integration with advanced storage and packaging technologies could further enhance its commercial applicability. This study also provided practical implications for commercial postharvest handling and export-oriented supply chains. Future studies should focus on molecular-level mechanisms and integration with packaging technologies.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eConflict of Interest\u003c/h2\u003e \u003cp\u003eThe authors declare that there is no conflict of interest regarding the publication of this manuscript.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eEthics Approval\u003c/strong\u003e \u003cp\u003e The authors confirm that all applicable guidelines and standards for plant research were followed during the course of this study.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eConceptualization and experimental design were carried out by TC and RP. Execution of the experiment, data collection, analysis and interpretation were performed by TC. Experimental materials were provided by P and RP. Manuscript preparation and editing were carried out by TC, RR, K, KS, RP and P. All authors read and approved the final manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eThe authors gratefully acknowledge the Horticulture Research Centre, Govind Ballabh Pant University of Agriculture and Technology (GBPUAT), Pantnagar, for providing the necessary facilities and support for conducting the experiment.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e \u003cp\u003eThe datasets generated and analysed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAbbasi, K.S., Anjum, N., Sammi, S., Masud, T. and Ali, S. 2011. Effect of coatings and packaging material on the keeping quality of mangoes (\u003cem\u003eMangifera indica\u003c/em\u003e L.) stored at low temperature. 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Oxford and IBH Publishing Co., New Delhi.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTanada-Palmu, P.S. and Grosso, C.F. 2005. Effect of edible wheat gluten-based films and coatings on refrigerated strawberry (\u003cem\u003eFragaria \u0026times; ananassa\u003c/em\u003e). Postharvest Biology and Technology, 36(2): 199\u0026ndash;208.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWills, R.B.G. and Rigney, C.J. 1979. Effect of calcium on activity of mitochondria and pectic enzymes isolated from tomato fruits. Journal of Food Biochemistry, 3(2): 103\u0026ndash;110.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYan, J., Luo, Z. and Ban, Z. 2019. Effect of layer-by-layer edible coating on strawberry quality and metabolites during storage. Postharvest Biology and Technology, 147: 29\u0026ndash;38.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYousaf, A.A., Abbasi, K.S., Ibrahim, M.S., Sohail, A., Faiz, M. and Khadim, M. 2024. Storage stability assessment of guava (\u003cem\u003ePsidium guajava\u003c/em\u003e L.) cv. \u0026lsquo;Gola\u0026rsquo; in response to different packaging materials. Sustainable Food Technology, 2(1): 210\u0026ndash;221.\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":false,"email":"","identity":"applied-fruit-science","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Applied Fruit Science","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"VoR Journals","inReviewEnabled":false,"inReviewRevisionsEnabled":false},"keywords":"Melatonin, postharvest physiology, shelf life, ambient storage, guava","lastPublishedDoi":"10.21203/rs.3.rs-9449990/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9449990/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003ePostharvest losses and rapid quality deterioration under ambient conditions remain major constraints in guava storage and optimal strategies for extending shelf life using naturally occurring plant growth regulator-like molecules are still not well established. This study evaluated the efficacy of postharvest melatonin (MT) application in enhancing shelf life and maintaining the quality of guava cv. Pant Prabhat stored under ambient conditions. Fruits were treated with various MT concentrations (0, 200, 400, 600 and 800 \u0026micro;M) and evaluated over a 15-day storage period. Results demonstrated a significant dose-dependent response, with 600 \u0026micro;M MT emerging as the optimal treatment. This concentration significantly reduced physiological loss in weight (11.34%), shrinkage (12.15%) and decay incidence (46.67%), while maintaining higher ascorbic acid (172.33 mg/100 g), total soluble solids (12.57 \u0026deg;Brix) and titratable acidity compared to the control. In contrast, the 800 \u0026micro;M dose showed reduced effectiveness, suggesting a possible metabolic threshold. Overall, melatonin application at 600 \u0026micro;M effectively delayed senescence and preserved fruit quality, highlighting its potential as a sustainable and non-toxic strategy for improving postharvest management and extending the marketable life of guava.\u003c/p\u003e","manuscriptTitle":"Optimal melatonin threshold for postharvest quality preservation of guava under ambient storage","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-28 11:53:14","doi":"10.21203/rs.3.rs-9449990/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"219955831539629034087062336612088336375","date":"2026-05-03T18:02:31+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"164510120809413846528134064816892546105","date":"2026-04-25T12:46:01+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-04-20T07:46:09+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-04-18T18:58:59+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-04-18T18:58:31+00:00","index":"","fulltext":""},{"type":"submitted","content":"Applied Fruit Science","date":"2026-04-17T13:40:49+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":false,"email":"","identity":"applied-fruit-science","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Applied Fruit Science","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"VoR Journals","inReviewEnabled":false,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"1e985303-55af-4991-a6f4-057b7ea926db","owner":[],"postedDate":"April 28th, 2026","published":true,"recentEditorialEvents":[{"type":"reviewerAgreed","content":"219955831539629034087062336612088336375","date":"2026-05-03T18:02:31+00:00","index":11,"fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-04-28T11:53:14+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-28 11:53:14","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9449990","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9449990","identity":"rs-9449990","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}