| In order to find out proper harvest stage and the reason leading to rapid softening process of fruits, two cultivars plum 'Gulf ruby' and 'Beauty' that were different in fruit texture were used as main materials to study physiological and biochemical changes and activity of main enzymes causing fruit softening of plum with different maturation degree. Physiological and biochemical changes of 'Gulf ruby' that was sprayed calcium solution before harvest were analyzed to investigate cultivation and management technology that could improve storage quality. In order to find a proper method and technology that could improve storage life and storage quality, different treatments such as heat shock, illumination and SA (Salicylic Acid) treatments during postharvest stage were used to half maturation plum to analyze their effects using 'Gulf ruby' and '86-7 plum' as materials. The main results were as follows:1 Peel color was found to be the standard of plum harvest. Storage life of yellow plum, half maturation plum and red maturation plum was 7, 5 and 4 days respectively at room temperature, and there was no significant difference in the quality of between half maturation plum and red maturation plum, but TSS content of the yellow plum was lower than the red maturation plum. Peel color of three kinds of maturation degrees plum was not significantly different. The 'Gulf ruby' should harvest in half maturation when the 'a' values of peel color appeared about -2.0 and the firmness of flesh about 8.5 X105Pa2 Flesh firmness of plum that was treated with calcium solution was significantly higher than the control. Furthermore, its starch content was significantly higher than the control in early stage of storage. And there is no significant difference between the two kinds from the third day after harvest. Preharvest calcium treatment was able to improve TSS content in fruit, but it has little effect on storage life and other quality index.3 Storage life of plum could be prolonged by 3 days by heat shock treatment after harvest compared with the control. The rate of starch and pectin decomposition, and the rate of ethylene production was slowed after heat shock treatment, but showed no significant difference in flavor and appearance quality compared with the control.4 Illumination treatment at low temperature had little effect on plum storage life and quality after harvest, and its color-changing rate was similar to the control at room temperature. Illumination treatment under low temperature could inhibit starchhydrolyzation. When plum fruits stored at low temperature were transferred to the room temperature, the starch content was declined rapidly.5 SA treatment after harvest reduced fruit ethylene production and decomposition rate of pro pectin, and had little effect on flavor and appearance quality. SA of three concentrations all could delay fruit softening process, and the most significant effect was observed for SA of 0.05mmol/L, while 5mmol/L had the least significant effect.6 Ethylene peak value of 'Gulf ruby1 fruit was significantly higher than that of 'Beauty', and the time when ethylene peak appeared was 6 to 8 days earlier than that of 'Beauty'. Softening of 'Gulf ruby' plum was very fast. Starch and pro pectin content of 'Gulf ruby' were higher than those of 'Beauty plum'. Starch and pectin content of 'Gulf ruby' declined rapidly, while those of 'Beauty' declined slowly.7 The main reason leading to 'Gulf ruby' softening was of starch and pectin decomposition according to the analysis of Amylase, PG and PME, and the decomposition of starch was increased during Amylase activity was increased. PG activity changing rate was stable softening process, while PME activity increased rapidly along with fruit softening. So, PME was mainly responsible for the hydrolyzation of pectin. Softening process of 'Gulf ruby' was slow at low temperature, and the main reason was the depressed amylase activity at low temperature.
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