猕猴桃软化过程中细胞壁修饰酶活性与果胶理化特性
摘要： 为探究低温贮藏中猕猴桃果实细胞壁修饰酶活性和细胞壁果胶多糖理化特性的变化规律，本研究以不同贮藏时期的猕猴桃果实为研究对象，测定了果肉质构和果实中多聚半乳糖醛酸酶（polygalacturonase, PG）、果胶甲酯酶（pectin methylesterase, PME）、果胶裂解酶（pectate lyases, PL）以及β-半乳糖苷酶（β-D-galaetosidase，β-Gal）等细胞壁修饰酶的活性。同时，分离得到三种细胞壁果胶多糖组分（水溶性多糖（water soluble polysaccharide, WSP）、CDTA溶性多糖（CDTA-soluble polysaccharide, CSP）和Na2CO3溶性多糖（Na2CO3-soluble polysaccharide，NSP）），并对其理化特性进行了研究。结果表明：猕猴桃果实的软化模式为“快速-缓慢”两段式。 PG在贮藏10 d出现最大值（670.76 U/mg）； PL和PME活性在贮藏5 d内增长幅度最大，分别为3.41 U/mg和9.17 U/mg。贮藏期间β-Gal的活性持续上升，与果实硬度呈显著负相关（r= -0.888）。WSP、CSP和NSP的含量随着贮藏时间的延长而呈现显著的增长。GPC结果表明贮藏期间WSP的分子量逐渐增大； CSP的分子量先减小后增加； NSP的分子量逐渐减小。SEM观察到WSP在贮藏的过程中面积减小且层叠度增大，CSP在贮藏15 d后呈柔软薄纱状，NSP团簇状堆积逐渐分散，碎屑增多。本研究旨在为阐明果实软化的详细机制提供一定的理论基础。
关键词: 猕猴桃, 果实软化, 果胶, 细胞壁修饰酶, 结构表征
Abstract: To explore the changes of cell wall modifying enzyme activities and the physicochemical properties of pectin polysaccharides of kiwifruit during low temperature storage, fruit hardness and the activities of polygalacturonase (PG), pectin methylesterase (PME), pectin lyases (PL) and β-galactosidase (β-Gal) in kiwifruit at different storage periods were determined. Meanwhile, the physicochemical properties of water soluble polysaccharide (WSP), CDTA-soluble polysaccharide (CSP) and Na2CO3-soluble polysaccharide (NSP) were further characterized in this study. Results showed that the kiwifruit went through "fast-slow" of softening. PG showed a maximum value of 670.76 U/mg at 10 d of storage; PL and PME activities showed a significant increase at 5 d of storage with 3.41 U/mg and 9.17 U/mg, respectively. Particularly, β-Gal activity continuously increased during storage and showed negatively correlated with fruit hardness (r= -0.888). The content of WSP, CSP and NSP increased significantly with the prolongation of storage time. Moreover, GPC results showed that the molecular weight of WSP increased while of NSP gradually decreased during storage. Furthermore, a decrease in the area and increase in the lamellarity of WSP was observed by SEM, whereas CSP was found to be soft and muslin after 15 d of storage, and the cluster-like accumulation of NSP was found gradually dispersed. Our results may provide a solid theoretical basis for elucidating the exact mechanism of fruit softening.
Key words: Kiwifruit, Fruit softening, Pectin, Cell wall modifying enzyme, Structural characterization
中图分类号:
TS201.4
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