Effect of Natural Antimicrobial Substances with Packaging System on Improving Quality of ‘ETMANI’ Guava (Psidium guajava L.) Fruit during cold storage

The effect of postharvest treatments of thyme oil and chitosan under different concentrations and combined with the packaging on weight loss%, firmness, decay index, malondialdehyde(MDA) content, total chlorophyll, hue angle (ho), ripening index, ascorbic acid and pectin methylesterase enzyme(PME) on  ‘Etmani’ guava (Psidium guajava L.) fruit, were investigated during 2017 and 2018 successive seasons. Obtained results indicate that weight loss %was diminished by (T7) thyme oil at 1000 μLL−1 + packaging and (T8) chitosan at 1% + packaging, as well as firmness and PME were reduced significantly (p˂0.05) when treated with chitosan at 1% and 2% (T3 and T 4) and thyme oil at 1000 μLL−1  ( T2) compared to control treatment (T0). Simultaneously, it indicated that the most effective treatment in decreasing  MDA and decay index were the treatment T3 and T4. Therefore, Chitosan and Thyme oils treatments could maintain normal cell membrane structure and function through down-regulating MDA content and pectin methylesterase enzyme activity, which due to reducing softening, weight loss%, and decay index in guava cv. ‘Etmani’ fruits during storage periods in comparison to other treatments and control