Degradation of water-soluble polysaccharides in pulp of litchi during storage

Abstract

Water-soluble polysaccharides (WSP) were extracted from the pulp of litchi. Its main component was identified as arabinogalactan. The dominant monosaccharide constituents were arabinose and galactose. Galactose and mannose accumulated at the end of storage. ATP, ADP and AMP levels declined with increasing pulp breakdown index. WSP depolymerized which was characterized by a decrease in its content and molecular weight, while its structure remained stable during storage. Polygalacturonase and pectate lyase (PL) were active at the early storage time, and β-galactosidase (GAL) and α-l-arabinofuranosidase followed thereafter. Except for some pectin methylesterase (LcPME), LcPL, LcGAL and LcPME gene expression was downregulated. It was deduced that depolymerization of polysaccharides was mainly caused by the rupture of the branched side chain and glacturonic acid backbone to smaller repeating units, and both cell wall-degrading enzymes and nonenzymatic factors, such as energy level, participated in the degradation of polysaccharides, and consequently pulp breakdown of litchi.

Keywords: Cell wall degrading enzymes; Energy status; Gene expression; Litchi chinensis; Pulp autolysis; Water-soluble polysaccharide.