Modification of cell wall polysaccharide during ripening of Chinese bayberry fruit

Experiments were conducted to investigate the modification of cell wall polysaccharide in Chinese bayberry during ripening. Cellular wall materials were isolated from Chinese bayberry fruit at four ripening stages. Three pectin fractions and two hemicellulose fractions were obtained and their compositional changes were analyzed. The process of ripening and softening of the fruit corresponded to an increase in the water soluble pectin (WSP) and 1mol/L KOH-soluble hemicellulose (HC1) fractions, and a decrease in Na2CO3-soluble pectin (SSP) and 4mol/L KOH-soluble hemicellulose (HC2) fractions which suggested the solubilization and conversion of cellular wall components. However, the content of CDTA-soluble pectin (CSP) changed slightly. Furthermore, arabinose, as the major branch monosaccharide, decreased in three pectin fractions during the whole ripening period, whereas the relative content of rhamnose, the backbone monosaccaride, tend to decrease in CSP and SSP pectin fractions, but increased gradually in WSP pectin during ripening. Analysis of (Ara+Gal)/Rha ratio showed that the degradation of WSP pectin mainly occurred in branch chains, conversely, the degradation of backbone played a more important role in degradation of CSP and SSP. In HC1, the breakdown of the branch chain of matrix xyloglucan, arabinoxylan and arabinogalactan are predominant while more backbones of xyloglucan, arabinoxylan and arabinogalactan were depolymerized in HC2. Moreover, it was found that the molecular weight of WSP decreased gradually throughout ripening while the depolymerization of ionic CSP and covalent SSP mainly occurred at late and early ripening stages, respectively. Loosely bound (HC1) and tightly bound (HC2) hemicellulose fractions exhibited distinct molecular mass downshift throughout ripening stages, especially at late ripening stage. Overall, fruit softening of Chinese bayberry during ripening involved in differential modification of pectin and hemicellulose.