Sunday, April 29, 2007

Hydrolysis of ammonia pretreated sugar cane bagasse with cellulase, ß-glucosidase and hemicellulase preparations

Bernard A. Prior and Donal F. Day. Audubon Sugar Institute, LSU Agricultural Center, 3845 Hwy 75, St Gabriel, LA 70776

Sugar cane bagasse is an attractive substrate for ethanol bioconversion. Approximately 24 and 38 % (dry weight) of bagasse consists of hemicellulose and cellulose respectively and bioconversion of both fractions to ethanol is recommended for a viable process. We have evaluated the degree of hydrolysis of pretreated bagasse with combinations of cellulase, β-glucosidase and hemicellulase. Ground bagasse was pretreated either by the AFEX process (2 NH3: 1 biomass, 100C, 30 min; kindly provided by MBI) or with ammonium hydroxide (0.5 g NH4OH of a 28 % (v/v) per g dry biomass; 160C, 60 min) and in both samples, the amounts of glucan and xylan fractions remained largely intact. The enzyme activities of 14 commercial enzyme preparations and supernatants of six laboratory grown fungi were determined. Eight preparations with significant xylanase activity were evaluated for their ability to boost xylan hydrolysis when used in combination with cellulase and β-glucosidase (10 FPU: 20 CBU/g glucan). When evaluated at a 1 % glucan loading, one commercial enzyme preparation (added at 10 % level of total enzyme protein) boosted xylan hydrolysis by at least 40 % of both pretreated bagasse samples. The glucan hydrolysis was also boosted by the xylanase. Xylanase addition at 10 % protein level also improved hydrolysis of xylan and glucan fractions up to 10 % glucan loading (28 % solids loading). Significant xylanase activity in enzyme cocktails appears to be required for greater hydrolysis of both glucan and xylan fractions of ammonia pretreated sugar cane bagasse.