关键词: 梨, 果实发育软化, 果胶多糖, 分子量分布, 酶活性

Abstract: 【Objective】The aim of this study is to investigate the relationship between the characteristics of cell wall pectin polysaccharide degradation and textural softening and storability of pear fruit, these results will further demonstrate the mechanism of fruit softening and provide a basis for improving fruit quality and developing better storage technology.【Method】Take the fruits of ‘Yali’ and ‘Jingbaili’ pears as the materials to compare the difference of the changes of pectin polysaccharide content, the molecular weight distribution and the related enzyme activity between two pear cultivars with different storabilities and textural properties during growth and softening.【Result】During development, in ‘Yali’ fruit, the content of both covalent soluble pectin (CSP) and ironic soluble pectin (ISP) increased rapidly, which were significantly higher than that of ‘Jingbaili’ fruit, and the water soluble pectin (WSP) content of ‘Yali’ fruit increased slowly which was lower than that of ‘Jingbaili’ fruit. Moreover, both WSP and CSP components were transferred from the low molecular weight to the high molecular weight in ‘Yali’ fruit. During storage, in ‘Yali’ fruit, the CSP showed a high and constant content with a slow increase in the content of WSP, which all maintained the higher molecular weight. But in ‘Jingbaili’ fruit, the CSP content decreased rapidly and a rapid increase showed in WSP and ISP content, and the pectin components were shifted from higher molecular mass to the lower ones. Moreover, changes of CSP, WSP and ISP contents were obviously related to fruit firmness only during development stage in ‘Yali’ fruit, but in ‘Jingbaili’ fruit, the changes of the contents of the three pectin compositions showed significant correlations with firmness loss mainly at stage of storage. The results indicated that it showed mainly the significant differences of pectin degrading enzymes activity between the two pear cultivars during storage, which the activities of polygalacturonase (PG), pectinmethylesterase (PME), β-galactosidase (β-Gal) and α-arabinofuranosidase (α-Af) and the increased rate in ‘Jingbaili’ fruit was significantly higher than that of ‘Yali’ fruit. Among them, β-Gal and α-Af activities increased rapidly just after harvest, while the increase date of PG and PME activities were relatively lagged and the correlations of the changes of β-Gal and α-Af activities with the changes of firmness and pectin components were stronger than that of PME and PG in ‘Jingbaili’ fruit, while in ‘Yali’ fruit only the change of α-Af activity had a significant relationship with the ISP content during storage. In summary, the pectin polysaccharide degradation showed significant differences between ‘Yali’ and ‘Jingbaili’ pear fruits and the related-factors played different roles at different softening stages, thus resulting in significantly different softening and storage characteristics.【Conclusion】The pectin polysaccharide fractions showed obvious accumulation of large molecular component and slowly degradated with fruit ripening in ‘Yali’ fruit, while the larger molecular components accumulated during fruit development degradated rapidly into smaller ones with fruit softening in ‘Jingbaili’ fruit. The insoluble pectin content and its molecular mass distribution may be an important index for measuring storability of pear fruit. Both β-Gal and α-Af played stronger roles in promoting ‘Jingbali’ fruit softening.

Key words: pear, fruit development and softening, pectin polysaccharide, molecular weight distribution, enzyme activity