Extended Abstract
1. Introduction: White button mushroom (Agaricus bisporus) is a widely consumed edible fungus with high nutritional value but a very short postharvest life due to rapid physiological deterioration. The absence of a protective cuticle, high respiration rate, and high moisture content make mushrooms highly perishable, leading to weight loss, browning, cap opening, and texture degradation during storage. Enzymatic browning, mainly associated with polyphenol oxidase activity, together with oxidative stress induced by reactive oxygen species (H₂O₂ and MDA), is a key factor accelerating senescence and quality loss. Edible coatings based on natural polysaccharides have been proposed as an eco-friendly method to extend the shelf life of fresh produce. Guar gum, a galactomannan polysaccharide, is of interest due to its film-forming ability and barrier properties against moisture and gas exchange, which may reduce respiration and delay quality deterioration. However, limited information exists on its application in mushrooms under cold storage. Therefore, this study evaluated the effect of guar gum coatings on the physicochemical, biochemical, and antioxidant quality of Agaricus bisporus during refrigerated storage.
2. Materials and Methods: Fresh white button mushrooms (Agaricus bisporus) were harvested from a commercial farm in Meimeh, Ilam Province, Iran, and transported to the laboratory under cooled conditions. Uniform samples were selected and divided into three groups: control (distilled water dip), 0.5% guar gum, and 1% guar gum (2 min immersion). After air-drying at 21°C, samples were packaged (10 mushrooms per container) and stored at 3 ± 1°C and 85-90% RH for 9 days. The experiment was arranged in a completely randomized design (CRD) in a factorial scheme with three replications. Data were analyzed using SAS (v9.2), and means were compared by Duncan’s test at the 5% significance level. Shelf life and quality attributes were evaluated based on cap opening, browning, weight loss, TSS, titratable acidity, protein, phenolics, flavonoids, PPO and PAL activities, hydrogen peroxide, malondialdehyde, and antioxidant capacity (DPPH assay).
3. Results and Discussion: Results demonstrated that guar gum coating had a significant positive effect on maintaining postharvest quality and extending the shelf life of white button mushrooms compared to the control. At the end of the storage period, untreated samples exhibited a shelf life of 9.3 days, whereas mushrooms treated with 0.5% and 1% guar gum showed extended shelf lives of 11.6 and 13.3 days, respectively. This improvement indicates the effectiveness of guar gum in delaying senescence and slowing down postharvest deterioration processes. Coated mushrooms showed markedly reduced weight loss, delayed cap opening, and lower browning intensity throughout storage. The superior performance of the 1% guar gum treatment suggests that higher coating concentration enhances the formation of a more effective semi-permeable barrier on the mushroom surface, which likely reduces water vapor loss and restricts gas exchange. Consequently, respiration rate and transpiration processes were suppressed, leading to improved visual and structural quality. From a biochemical perspective, guar gum-coated samples maintained significantly higher levels of total soluble solids, titratable acidity, protein content, total phenolics, and flavonoids compared to the control during storage. The preservation of these quality-related compounds suggests that the coating effectively slowed down metabolic activities and delayed the degradation of key nutritional and bioactive constituents. In particular, the higher retention of phenolic and flavonoid compounds in coated samples reflects improved stability of antioxidant-related metabolites during storage. Enzymatic results further supported these findings, as guar gum coating significantly reduced polyphenol oxidase (PPO) activity while maintaining higher phenylalanine ammonia-lyase (PAL) activity. The suppression of PPO activity indicates a reduction in enzymatic browning, whereas the sustained PAL activity suggests continued biosynthesis of phenolic compounds and delayed senescence. These enzymatic modifications collectively contributed to better visual quality and slower deterioration in coated mushrooms. Moreover, oxidative stress indicators revealed that guar gum coating effectively reduced the accumulation of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA), both of which are key markers of oxidative damage and lipid peroxidation. The lower levels of these compounds in coated samples indicate that the coating helped mitigate reactive oxygen species accumulation and protected cellular membranes from oxidative injury during storage. Although antioxidant capacity decreased progressively in all treatments over time, coated mushrooms, particularly those treated with 1% guar gum, consistently exhibited significantly higher antioxidant activity compared to the control. This suggests that the coating not only slowed down oxidative degradation but also helped preserve the functional antioxidant system of the mushrooms during storage.
4. Conclusion: The present study demonstrates that guar gum coating is an effective natural and biodegradable approach for maintaining postharvest quality of white button mushrooms during refrigerated storage. The application of guar gum significantly reduced weight loss, delayed browning and cap opening, and preserved nutritional and bioactive compounds. Furthermore, guar gum coating reduced oxidative stress and modulated key enzymatic activities associated with senescence. Among the tested concentrations, 1% guar gum was most effective at maintaining overall quality and extending shelf life. In conclusion, guar gum can be recommended as a safe and cost-effective edible coating for improving the postharvest storage life of Agaricus bisporus under cold storage conditions. Further studies are suggested to evaluate its combination with other natural coatings or antimicrobial agents to enhance preservation efficiency.