The activities of several stage specific enzymes (SSE) and the changes of some compounds during softening of “Qinmei” kiwifruit (Actinidia deliciosa) were studied. The resuits showed that there were two phases of kiwifruit softening. Firstly the rapid softening phase was coincided with starch degradation (r= 0. 99) and the increase of amylase activity. It suggested that amylase was the key SSE for softening at this phase. In the second phase, the rate of softening was decreased, the contents of water insoluble pectin and cellulose apparently were reduced and the activities of polygalacturoase (PG) and cellulase were markedly increased, which indicated the PG and cellulase were the key SSE in the second softening phase. Besides, ethylene forming enzyme (EFE) activity and ethylene production were at their peaks between the two phases as they might play the part as triggers of the PG and cellulase activities. The experiments also showed that the activity of pectin methylesterase (PME) was not related to the softening of kiwifruit. The maximum activities of peroxidase (POX), catalase (CAT) and superoxide dismutase (SOD) were found after the softening stages. It seemed that they were not the key SSE for the softening of kiwifruit.
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