猕猴桃果实软化过程中细胞壁多糖物质含量与果胶降解相关酶活性变化

Changes of polysaccharide content and pectin degradation related enzyme activities in cell wall during softening of kiwifruit

为研究不同贮藏温度下不同品种猕猴桃果实软化过程中细胞壁多糖物质降解特性,以及相关果胶降解酶对猕猴桃果实软化进程的影响,测定25℃和4℃贮藏过程中徐香、金丽、晚绿猕猴桃果实的硬度、细胞壁多糖物质含量和果胶降解相关酶活性,并对其进行相关性分析。结果表明,3个品种猕猴桃果实软化过程中半纤维素、纤维素和共价型果胶(covalent soluble pectin,CSP)含量不断降低,水溶性果胶(water soluble pectin,WSP)含量不断增加,而离子结合型果胶(ionic soluble pectin,ISP)含量相对稳定。晚绿猕猴桃各细胞壁多糖组分含量变化速度最快,金丽次之,徐香最慢。4℃贮藏延缓了猕猴桃果实细胞壁多糖物质的降解。相关性分析结果表明,3个品种猕猴桃果实硬度与WSP含量之间均呈显著(P<0.05)负相关,与CSP、半纤维素、纤维素含量之间呈显著正相关。果胶降解酶活性测定结果显示,25℃贮藏前期,晚绿猕猴桃内切多聚半乳糖醛酸酶(endo-polygalacturonase,PG)和β-半乳糖苷酶(β-galactosidase,β-Gal)活性显著高于其他两个品种,徐香猕猴桃PG和β-Gal的活性显著低于其他两个品种;4℃贮藏前期,晚绿猕猴桃中果胶酸裂解酶(pectate lyase,PL)和α-L-阿拉伯呋喃糖苷酶(α-L-arabinofuranosidase,α-AF)活性显著高于其他两个品种,徐香猕猴桃中PL和α-AF活性显著低于其他两个品种。25℃贮藏条件下,与徐香果实软化显著相关的果胶降解酶是PG和β-Gal;4℃贮藏条件下,与徐香果实软化显著相关的果胶酶是α-AF和果胶甲酯酶(pectin methylesterase,PME);与金丽和晚绿果实软化显著相关的果胶酶分别是α-AF和PL。综上所述,软化最快的晚绿猕猴桃细胞壁多糖组分含量变化最快,软化最慢的徐香猕猴桃细胞壁多糖组分含量变化最慢。25℃贮藏前期,PG和β-Gal活性在晚绿中最高,在徐香中活性最低;4℃贮藏前期,PL和α-AF的活性在晚绿中最高,在徐香中最低。这些果胶酶活性的差异是导致晚绿果实软化较快而徐香果实软化较慢的原因之一。

To investigate the degradation characteristics of cell wall polysaccharides and effects of related pectin degrading enzymes on the softening process of kiwifruit fruits at different storage temperatures.Fruit firmness,cell wall polysaccharide content and pectin degradation related enzyme activities of Xuxiang,Jinli and Wanlv fruits during storage at 25℃and 4℃were determined,and their correlation was analyzed.The firmness of Wanlv decreased the fastest and the storage time was the shortest,while the firmness of Xuxiang changed the slowest and the storage time was the longest.With fruit softening,contents of hemicellulose,cellulose and covalent soluble pectin(CSP)in kiwifruit of these three cultivars showed a decreasing trend,content of water soluble pectin(WSP)showed an increasing trend,while content of ionic soluble pectin(ISP)was relatively stable.The degradation rates of cell wall components of different cultivars were different at the two storage temperatures.Change rate of polysaccharide components in Wanlv kiwifruit was the fastest,followed by Jinli and Xuxiang.Storage at 4℃delayed the degradation of cell wall polysaccharides.The results of correlation analysis showed that there was a significant(P<0.05)negative correlation between fruit firmness and WSP content,and a significant positive correlation between fruit firmness and CSP,hemicellulose and cellulose content in three varieties of kiwifruit.The results of pectin degradation enzyme activity determination showed that PG andβ-Gal activities of Wanlv were significantly higher than those of the other two cultivars at 25℃,and PG andβ-Gal activities of Xuxiang kiwifruit were significantly lower than those of the other two cultivars.In the early stage of storage at 4℃,activities of PL andα-AF in Xuxiang were significantly lower than those of the other two cultivars.At 25℃,PG andβ-Gal were the pectin degrading enzymes that was significantly related to the softening of Xuxiang fruit.Under 4℃storage condition,the enzymes significantly related to fruit softening of the three kiwifruit cultivars were different.The pectinase that was significantly related to the softening of Xuxiang fruit wasα-AF and PME.The pectinases significantly associated with the softening of Jinli and Wanlv fruits wereα-AF and PL,respectively.Wanlv kiwifruit softened the fastest,and its cell wall polysaccharide content changed the fastest.The softening rate of Xuxiang kiwifruit was the slowest,and the change of polysaccharide content in cell wall was also the slowest.In the early stage of storage at 25℃,the activities of PG,β-Gal andα-AF in Wanlv were the highest,while the activities of PME,PG,PL,β-Gal andα-AF in Xuxiang were the lowest.In the early stage of storage at 4℃,PL andα-AF activities were the highest in Wanlv,and the lowest in Xuxiang.These differences in pectinase activity may be one of the reasons for the rapid softening of Wanlv fruit and the slow softening of Xuxiang fruit.