Chitosan elicits antioxidant defense mechanisms and alters oxidative stress-associated browning responses in postharvest apples
1Fruit Crops Handling Research Department, Chemical Analysis Central Laboratory, Horticulture Research Institute (HRI), Agricultural Research Center (ARC), Giza, Egypt. 2Deciduous Fruits Research Department, Biotechnology Central Laboratory, Horticulture Research Institute (HRI), Agricultural Research Center (ARC), Giza, Egypt, Corresponding e-mail: raaniaahmed@arc.sci.eg
DOI: https://doi.org/10.37855/jah.2026.v28i02.70
Oxidative stress plays a central role in postharvest browning of apples, particularly following mechanical wounding. Chitosan is considered a promising preservative that enhances stress tolerance and maintains postharvest fruit quality. The study explored antioxidant defense mechanisms elicited in response to mechanical damage-induced oxidative stress in four apple cultivars differing in their susceptibility to browning for providing integrated insights into cultivar-specific defense strategies. Wounding induced the accumulation of reactive oxygen species (ROS), whereas chitosan treatment elicited antioxidant defense mechanisms, effectively modulating ROS metabolism and preventing the loss of membrane integrity. The responses varied significantly among the tested cultivars, reflecting inherent differences in browning susceptibility. Golden Delicious accumulated high malondialdehyde (MDA) levels, accompanied by peak cell membrane leakage. Royal Gala exhibited reduced phenylalanine ammonia-lyase (PAL) activity under all conditions and generally contained the lowest levels of total phenolics. In contrast, Red Delicious was characterized by the highest phenolic content along with elevated activities of polyphenol oxidase (PPO) and peroxidase (POD); these enzymatic activities were further stimulated under stress conditions. Granny Smith exhibited a significant increase in PAL activity in response to all treatments, with relatively high phenolic content ranking second only to Red Delicious. It also showed the highest H2O2-scavenging activity, while maintaining lower cell membrane permeability under all conditions. Furthermore, Granny Smith showed lower POD enzyme activity, followed by Royal Gala. The diversity among apple cultivars allowed investigation of how POD activity and its isoforms are involved in oxidative stress-associated potential browning responses and antioxidant defense mechanisms.
