Production of narrow-range size-classes of polygalacturonic acid oligomers

A structural component of citrus processing residues with significant functionality is the homogalacturonan region of pectin. Its functional properties include ion binding, gelation, water retention and elicitation of plant defense responses to pathogens. It is also the site of attack by commercial pectinolytic enzymes used as processing aids for viscosity reduction, enzymatic peeling and conversion of peel polysaccharides to monomeric sugars for subsequent fermentation. More recently endo-polygalacturonases (EPG) have been used as research tools to probe the mode of action of pectin methylesterases and to map pectin fine structure. Consequently, knowing how EPG acts on oligomers of polygalacturonic acid is needed. A major limitation in studying these oligomers has been the limitations on chromatographic detection. In the work presented here, three size-classes with a degree of polymerization ranging from 1-13, 8-24 and 22-46 were prepared by enzymatic digestion followed by a combination of differential pH and alcohol precipitation. The oligomers were characterized using improved chromatographic techniques that enabled us to estimate masses of individual oligomers. Strawberries were treated with each size-class to determine if the fragments elicited a biological response. Only the medium-DP size-class resulted in a delay in fruit decay not observed with the low-or high-DP size-classes.