Enhanced Enzymatic Digestibility of Crystalline Cellulose After AFEX Treatment: The Role of Cellulose I Conversion to Other Alloforms

AFEX (ammonia fiber expansion) pretreatment of lignocellulosic biomass substantially increases the rate and extent of enzymatic digestion of glucan and xylan. Using crystalline cellulose (Avicel) as a model substrate to study the effect of AFEX on cellulose has several advantages since it is free of lignin and hemicellulose. Ongoing experiments have shown that AFEX treatment with liquid ammonia under certain conditions significantly enhances the rate of cellulose digestion (by 2-5 folds) to glucose by commercial and purified cellulolytic enzymes. Severe AFEX pretreatment (at high ammonia loading, moisture, temperature and residence time) has the opposite effect of decreasing digestion. AFEX pretreated cellulose digestibility will be correlated to X-ray diffraction patterns and to FT-Raman spectra. By this approach, we can develop a fundamental understanding of the conditions under which native cellulose I is converted to other alloforms (Cellulose II, III) and the resultant effect on enzymatic digestion.