不同品种苹果采后后熟软化过程中细胞壁多糖的降解

Degradation of Cell Wall Polysaccharides during Postharvest Fruit Rip-ening and Softening of Different Apple Varieties

以2种苹果为试材,提取了不同贮藏时期果实的细胞壁物质和8种细胞壁多糖组分,并采用气相色谱法分析了细胞壁多糖组分的单糖组成。结果表明,在贮藏过程中,‘金星’苹果果肉的硬度下降明显,在贮藏第10天前后出现明显的乙烯释放量高峰,而耐贮藏性‘富士’苹果在贮藏期间只释放极少量的乙烯。‘金星’苹果的Na2CO3-1溶性果胶多糖组分的减少尤为显著。这些结果表明,苹果果实Na2CO3-1溶性果胶多糖组分侧链成分的酶降解,是引起苹果细胞壁多糖网络结构的变化,进而导致果实软化的重要原因之一。

The cell wall material （CWM） and eight cell wall polysaccharides fractions were extracted from ‘Fuji＇ and ‘Kinsei＇ apples during storage at different time （0 and 42 days）. The sugar composition characteristics of each fraction were determined by gas chromatography. The results showed that, during storages, the firmness of ‘Kinsei＇ apples decreased significantly （Fig. 1）, and a significant peak of ethylene production was shown after 10 d storage, but only a little ethylene was produced in ‘Fuji＇ apples, which had a better storability （Fig.2）. Compare to other cell wall polysaccharide fractions, in Na2CO3-soluble pectic fractions of apple fruit, there were abundant rhamnogalacturonan Ⅰ（RG-Ⅰ）, which branched highly in side chains due to the compositions of arabinans, galactans, arabinogalactans etc （Tables 2-5 and Fig.4）. As for cell wall polysaccharides, in ＇Kinsei＇ apples, the decrease of pectic fractions was shown most significantly in NaECO3-1 fraction （Table 1 and Fig.3）, which was associated with a significant degradation of arabinosyl and galactosyl residues on the side chains （Table 3）. Further more, higher molecular mass in Na2CO3-1 pectic polysaccharides degraded and turned into ones with smaller molecular mass （Fig.5）. From these results, the degradation of side chains in Na2CO3- 1 pectic polysaccharides under the activity of enzyme was considered one of the most significant factors of apple fruit softening through modifying the network of cell wall polysaccharides.