Effects of short-term N2 treatment on lipid peroxidation, anti-oxidant enzymes and flesh softening of kiwi fruits during cold storage
Flesh softening is the main limitation to the postharvest storage, handling and marketing life of kiwifruit. Evidences suggest that pre-storage treatment with pure N2 gas is potentially effective in inhibiting senescence of many harvested horticultural crops. To better understand the role of short-term N2 treatment in softening of kiwi fruit, flesh firmness, malondialdehyde (MDA) and hydrogen peroxide (H2O2) contents, superoxide anion (O2.-) production rate, as well as activities of lipoxygenase (LOX), peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT) were investigated. Kiwifruits were exposed to pure N2 gas for 6 h, and then kept in closed but vented containers for 35 days in the dark at 0-1°C and 95-100% relative humidity. Flesh firmness decreased rapidly during the cold storage time, and short-term N2 treatment inhibited the decrease in flesh firmness, particularly the rapid decrease within 7 days of the early storage, which suggested pure N2 could delay flesh softening of kiwi fruits at 1°C. MDA content, O2.- production rate and H2O2 content increased in kiwifruit with storage time. Short-term N2 treatment showed a lower level of lipid peroxidation compared to non-N2 treated fruit, with a delay in increasing in both O2.- production rate and H2O2 content. SOD, CAT and POD activities of the fruits markedly decreased during the cold storage, while LOX activity showed a maximum value on day 7, followed by a decline. The treatment with pure N2 increased activities of SOD, CAT and POD, and decreased LOX activity. These data indicated that short-term N2 treat¬ment delayed softening of cold stored kiwifruit involve alleviating lipid peroxidation via suppressing oxidative damage and enhancing antioxidant defense.