HEAT SHOCK REDUCES BOTH CHILLING INJURY AND THE OVERPRODUCTION OF REACTIVE OXYGEN SPECIES IN YELLOW PITAYA (HYLOCEREUS MEGALANTHUS) FRUITS

Yellow pitaya fruits were heat-shocked (25C/24 h), stored at 2C for 14 days and then held for 13 days at 18C. Chilling injury (CI), respiration rate, hydrogen peroxide (H2O2), superoxide anion radical (O2 center dot-) and lipid peroxidation product (LPP) levels were measured. Pitting and browning were detected in the control fruit when moving from 2 to 18C. Minor CI symptoms were found in the treated fruit. There was a rapid increase in the levels of H2O2, O2 center dot- and LPP in the control fruits when moved to 18C. At the end of the storage, the levels of these compounds were 4.5-, 4.9- and 6.2-fold higher, respectively, in the control than in the treated fruit. The results suggest that the reactive oxygen species levels in the heat-shocked fruit were adequate for normal ripening, while the levels in the control group were excessively high, inducing CI symptoms.