COMPARATIVE ENZYME BIODEGRADABILITY OF XYLAN, CELLULOSE, AND STARCH DERIVATIVES

The enzyme biodegradability of xylan and of two of its prominent derivatives, (hydroxypropyl)xylan and xylan acetate, were examined comparatively vis-a-vis similar cellulose and starch derivatives, using a commercially available xylanase-rich enzyme preparation. The results indicate that xylan, like cellulose and its derivatives, is subject to enzymatic depolymerization in relation to degree of substitution. Degradation paralleled the presence of unmodified xylose units in the polysaccharide. Degradation proceeded rapidly, with greater than 80% of total degradation being complete after only 1 day. A comparison with starch and cellulose derivatives revealed that hydroxypropyl xylan suffers less biodegradability loss as substitution rises to 0.25 or 0.4, after which loss of degradability parallels that of the corresponding cellulose and starch derivatives. This apparent tolerance to low degrees of substitution is attributed to molecular heterogeneity which suggests that constituents other than xylose become propoxylated initially. Xylan acetate was found to lose enzymatic biodegradability at a rate which parallels that of cellulose acetate, and this is 35% slower (with respect to DS) than corresponding starch acetates. Size exclusion chromatography results suggest that xylan degrades to monosaccharides, that xylan derivatives degrade to monosaccharides and oligosaccharides, and that substitution with lignin prevents xylan from being recognized by xylanolytic enzymes, resulting in loss of degradability.