猕猴桃软化过程中阶段性专一酶活性变化的研究

STUDY ON THE ACTIVITIES OF STAGE SPECIFIC ENZYME DURING SOFTENING OF KIWIFRUIT

猕猴桃（Ａｃｔｉｎｉｄｉａ ｄｅｌｉｃｉｏｓａ Ｃ．Ｆ．Ｌｉａｎｇ ｅｔＡ．Ｒ．Ｆｅｒｇｕｓｏｎ． ｃｖ． Ｑｉｎｍ ｅｉ）果实采后的软化过程表现为两个明显的阶段，第一阶段软化较快，此时对软化起主要作用的阶段性专一酶是淀粉酶；第二阶段软化速度变慢，此时起主要作用的阶段性专一酶是多聚半乳糖醛酸酶和纤维素酶。乙烯形成酶（ＥＦＥ）的活性高峰出现在两个软化阶段之间，它所引起的乙烯释放对软化有促进作用，因此ＥＦＥ也是与果实软化有关的阶段性专一酶。但是，果胶甲酯酶（ＰＭＥ）的活性变化与果实的软化无相关关系，过氧化物酶（ＰＯＸ）、过氧化氢酶（ＣＡＴ）和ＳＯＤ的活性高峰出现在果实完全软化以后。

The activities of several stage specific enzymes (SSE) and the changes of some compounds during softening of 'Qinmei' kiwifruit (Actinidia deliciosa) were studied. The results 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.