Structural features of hairy regions of pectins isolated from apple juice produced by the liquefaction process

Abstract

A high-molecular-weight pectic fraction, released from the cell walls of apple tissue by pectolytic, hemicellulolytic, and cellulolytic enzymes, was isolated from apple juice prepared by the liquefaction process. The fraction, termed modified hairy regions (MHR), was characterized as a highly branched rhamnogalacturonan with arabinose-rich side chains and represented 0.26% of the fresh apple. Arabinose was the most abundant sugar (55 mol%) in MHR, which had a high rhamnose-galacturonic acid ratio (0.29) and degrees of methylation and acetylation of 42% and 60%, respectively. The sugar and linkage compositions, distribution of molecular weights, susceptibility to .beta.-elimination mediated by alkali and 4-methylmorpholine N-oxide, and the effect of various technical and pure enzymes on MHR and chemically and enzymically modified MHR have been studied. From the results and 13C-n.m.r. data, a tentative structure for MHR is proposed.