Structural Changes in the Cell-Wall Pectic Polysaccharides Accompanied by Softening of Apple (Malus pumila Mill.) Cultivars Fuji and Kinsei

Abstract

Cell wall material (CWM) prepared from apple cultivars, cv. Fuji with excellent storability and cv. Kinsei with poor storability, before and after storage were fractionated into four pectic polysaccharide fractions (CDTA-1, CDTA-2, Na2CO3-1 and Na2CO3-2), three hemicellulose fractions (KOH-1, KOH-2 and KOH-3) and CWM residue (cellulose rich fraction). Quantitative changes of their fractions from apple cultivars with different storability before and after storage were also compared. In cv. Fuji, the weight of each fraction changed only slighting after storage for 42 day at 20°C, but in cv. Kinsei, the weight of Na2CO3-1 fraction containing pectic polysaccharides decreased most markedly among 8 fractions after storage for 42 days at 20°C. The analysis of monosaccharide composition of Na2CO3-1 fraction showed that the release of arabinose and galactose from the pectic polysaccharide was markedly higher in cv. Kinsei than in cv. Fuji after storage for 42 days at 20°C, suggesting that the reduction of Na2CO3-1 fraction is closely correlated with the release of arabinose and galactose moieties from the pectic polysaccharide of Na2CO3-1 fraction accompanied by softening. This suggests that degradation of bulky arabinogalactan side chain in major pectic substances, rhamnogalcturonan I in Na2CO3-1, may have an important role in the softening process of apples.