Postharvest chitosan treatment affects quality, antioxidant capacity, antioxidant compounds and enzymes activities of 'El-Bayadi' table grapes after storage

The effect of postharvest chitosan treatments at 1, 1.5 and 2% on quality, antioxidant capacity, antioxidant compounds and some related enzymes activities of 'El-Bayadi' table grapes after 30 days of storage plus 2 days of shelf life were investigated. Chitosan treatments decreased decay after storage (ranged from 2.95 to 4.42%) compared to control (16.25%). However, weight loss was lower only at 1% chitosan (0.39%) than other rates and control (1.66). Quality characteristics TSS, acidity and pH of berries slightly changed after storage compared to initial and were not affected by chitosan treatments. However, berry firmness decreased after storage, but chitosan treatments retained higher firmness than control. Chitosan treatments, especially at 1%, maintained higher total phenols and flavonoids concentration than control. Total phenols concentration decreased as chitosan rate increased, in contrast to total flavonoids. However, vitamin C concentration showed higher values after storage than initial and was not affected by chitosan treatments. Peroxidase (POD) showed higher activity after storage, in all treatments, than initial and was higher in chitosan treatments than control. POD activity increased as chitosan rate increased. Polyphenoloxidase (PPO) showed lower activity after storage in control compared to initial. While, chitosan treatments maintained higher PPO activities than control. Both polygalacturonase (PG) and xylanase activities slightly changed after storage in most treatments compared to initial. However, chitosan treatments maintained higher PG and xylanase activities than control. Both PG and xylanase activities increased as chitosan rate increased. Antioxidant capacity measured by the DPPH method decreased after storage in control compared with initial. Chitosan treatments showed higher antioxidant capacity than control. However, antioxidant capacity measured by the ABTS method was not affected by chitosan treatments. It is concluded that chitosan treatments enhanced antioxidant systems, retained and improved quality of 'El-Bayadi' table grapes after storage.