Antioxidant enzyme activity and chilling injury during low-temperature storage of Kiwifruit cv. Hongyang exposed to gradual postharvest cooling

Kiwifruits (Actinidia chinensis cv. Hongyang) were treated by direct cooling and gradual cooling to investigate the effect of cooling treatment on chilling injury. The direct cooling fruits were immediately cooled at 0A degrees C after harvest. The gradual cooling fruits were held for 3 days at 5 A degrees C (from 5 A degrees C to 0A degrees C), or for 7 days at 2A degrees C (from 2A degrees C to 0A degrees C), or decreased in temperature from 15A degrees C to 5A degrees C by 5A degrees C at 1 days intervals and then maintained at 5A degrees C for 3 days plus a subsequent period of of 7 days at 2 (from 15A degrees C to 0A degrees C). After the above treatments, then those fruit were stored at 0 +/- 0.5A degrees C, 90% to 95% RH for 80 days. Gradual cooling (from 15A degrees C to 0A degrees C) significantly maintained higher percentage of accepted fruit and lower chilling injury index and chilling injury incidence of fruit compared with the direct cooling. Some attributes were then assayed in the fruits treated with gradual cooling (from 15A degrees C to 0A degrees C). Gradual cooling (from 15A degrees C to 0A degrees C) inhibited increases in membrane permeability, malondialdehyde content, superoxide anion production rate, and H2O2 content. At the same time, fruit cooled gradually (from 15A degrees C to 0A degrees C) exhibited higher superoxide dismutase, catalase, ascorbate peroxidase, and peroxidase activities than those treated by direct cooling during storage. The present study indicated that enhancement in antioxidant enzyme activity may be attributed to the reduction in CI symptoms by the gradual cooling treatment (from 15A degrees C to 0A degrees C).