The Effect of Edible Coating with Alginate and Shirazi Thyme Essential Oil on the Qualitative Characteristics of Ber Fruit (Ziziphus mauritiana Lam.) during Storage

Introduction Ziziphus mauritiana, also known as Ber fruit, is a tropical fruit from the Rhamnaceae family with high nutritional value and a short shelf life. Edible coatings the surface of the fruit can play a positive role in increasing its shelf life. The application of alginate (Al), a linear polysaccharide derived from brown seaweed (Macrocystis pyrifera), which has the advantage of moisture retention, and also Shirazi thyme (Zataria multiflora) essential oil (ZEO), which contains antioxidant and antimicrobial compounds, can improve the fruit's characteristics and preserve its quality for a longer period. In recent years, the application of ZEO together with organic coatings in order to enhance the quality characteristics of different fruits during storage has been the focus of researchers. This study aims to investigate the effect of alginate coating and ZEO on the post-harvest and physicochemical characteristics of Ber fruit during storage at 6±1 C˚ and a relative humidity of 90-95%.   Material and Methods This study was conducted to enhance the shelf life of Ber fruits by treating them with alginate (Al) and Shirazi thyme essential oil (ZEO). Ber fruits at their mature green stage were harvested in 2022 from a commercial orchard in Minab, Hormozgan province. After harvesting, the fruits were transported to the Horticulture Laboratory University of Hormozgan, to apply the treatments. Factors include six treatments (control, Shirazi thyme essential oil 0.5%, Shirazi thyme essential oil 1%, alginate, alginate + Shirazi thyme essential oil 0.5% and alginate + Shirazi thyme essential oil 1%) and five storage periods(zero, 7, 14, 21, 28 days). The treated fruits were then stored at 6±1 C˚, and relative humidity of 90-95% for 28 days. The factorial experiment was conducted as a completely randomized design with four replications, and ten fruits were used in each replication. Fruit parameters such as fruit weight loss, respiration rate, total soluble solids (TSS), organic acid, ascorbic acid, fruit firmness, carotenoids, and chlorophyll content were evaluated. Statistical analysis of data was done using SAS software. Figures were drawn using Excel software.   Results and Discussion Based on the results of the analysis of variance, the main effects of time and treatment were significant (P<0.01) for all characteristics. Additionally, the interaction effect of treatment and time was significant (P<0.01) for all traits except for ascorbic acid. Comparisons of means showed that all treatments, maintained fruit quality compared to the control. The Al + ZEO treatment had a significant effect on reducing respiration rate. This combined treatment reduced weight loss, decay percentage, and fruit softening while slowing down the increase in TSS. The alginate coating and Shirazi thyme essential oil delayed ripening and subsequent fruit softening by reducing ethylene activity. Furthermore, the coated fruits had higher levels of ascorbic acid compared to the untreated fruits. These coatings are impermeable to water vapor and create a saturated atmosphere, preventing fruit evaporation and wrinkling, thus delaying ripening. The use of essential oils in the form of a semi-permeable layer also reduces respiration and surface transpiration by inhibiting the movement of oxygen, carbon dioxide, and moisture, playing a positive role in preserving fruit quality.   Conclusion The aim of this study was to investigate the effect of alginate coating and Shirazi thyme essential oil on the post-harvest and physicochemical characteristics, as well as the shelf life of Ber fruit. The results clearly indicated the enhancement of fruit quality using edible coatings compared to the control. The combination of Al + ZEO (0.5%) had significantly positive effects on preserving the postharvest quality of Ber fruit. In fact, by creating a semi-permeable coating on the surface of the fruit, thyme essential oil and alginate lead to limiting the fruit respiration and metabolism and fungi growth, thus delaying the ripening process, increasing TSS and ascorbic acid and total acidity. According to these results, to reduce post- harvest losses and increase productivity of fruit, the use of 0.5% Shirazi thyme essential oil in combination with alginate coating is recommended due to its beneficial effects on the appearance and physicochemical characteristics of Ber fruit during storage.   Acknowledgement The authors of this article express their gratitude and appreciation for the financial support from the Hormozgan Science and Technology Park and the University of Hormozgan.