COMPARATIVE ENZYME BIODEGRADABILITY OF XYLAN, CELLULOSE, AND STARCH DERIVATIVES

The enzyme biodegradability of xylan and of two of its prominent deriv atives, (hydroxypropyl)xylan and xylan acetate, were examined comparat ively vis-a-vis similar cellulose and starch derivatives, using a comm ercially available xylanase-rich enzyme preparation. The results indic ate that xylan, like cellulose and its derivatives, is subject to enzy matic depolymerization in relation to degree of substitution. Degradat ion paralleled the presence of unmodified xylose units in the polysacc haride. 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 le ss biodegradability loss as substitution rises to 0.25 or 0.4, after w hich loss of degradability parallels that of the corresponding cellulo se and starch derivatives. This apparent tolerance to low degrees of s ubstitution is attributed to molecular heterogeneity which suggests th at 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 resp ect to DS) than corresponding starch acetates. Size exclusion chromato graphy results suggest that xylan degrades to monosaccharides, that xy lan derivatives degrade to monosaccharides and oligosaccharides, and t hat substitution with lignin prevents xylan from being recognized by x ylanolytic enzymes, resulting in loss of degradability.