The Effect of Cellulases on the Biodegradation and Morphology of Naturally Colored Cotton Fibers

The effect of cellulases on the biodegradation and structure of natural colored cotton (FoxFibre) was examined. Cottons containing brown pigments, the varieties Buffalo (mocha brown) and Coyote (reddish brown), were quite resistant to hydrolysis by Trichoderma reesei cellulase (Celluclast) and purified cellobiohydrolase I (CBH I) and endoglucanase II (EG II), while white and Palo Verde (sage green) varieties derived from the same germplasm stock were more susceptible to hydrolysis. No differences in the binding isotherms of CBH I and EG II to the different FoxFibre cottons were observed. Atomic force microscopy of the colored cotton fibers treated with CBH I detected peeling of the outer surface. The surface of cotton fibers treated with EG II appeared to be smoothed or polished. After alkaline extraction of the pigments, the brown cottons were rapidly hydrolyzed by Celluclast, CBH I, or EG II. Extracts of the colored cotton contained yellow pigments with absorption peaks at 270 nm. The extracts were found to be strong inhibitors of cellulase activity, but had no effect on β-glucosidase. Incubation of the extracts with β-glucosidase decreased the inhibition of cellulases. Analysis with nmr, IR, and hplc indicated that the extracted pigments were associated with oligosaccharides.