Bioconversion of hemicellulose: aspects of hemicellulase production by Trichoderma reesei QM 9414 and enzymic saccharification of hemicellulose.
The growth of Trichoderma reesei QM9414 in shake flasks at 28 degrees C on hemicellulose substrates and bagasse resulted in rather low yields of hemicellulolytic enzymes (1.0-1.5 units/mL xylanase and 0.05-0.08 units/mL beta-xylosidase). The influence of pH on the synthesis of beta-xylosidase was greater than on the synthesis of xylanase. Both xylanase and beta-xylosidase showed optimal activity at pH 4-5 and 55-60 degrees C. Xylanase was stable at pH 2-10 but was heat labile and totally inactivated after 1 h at 65 degrees C. Enzyme stability towards heat could be increased in the presence of bovine serum albumin. The beta-xylosidase was more tolerant to heat, but stable over a pH range 2.5-6.0. The D-xylose inhibited both enzymes in a competitive manner. Hemicellulose (heteroxylan) was degraded to the extent of 30-40%within 24 h. The degree of hydrolysis decreased as the substrate concentration increased and increased with increased amounts of enzyme. Multiple enzyme doses resulted in increased saccharification in reduced times. The degree of hydrolysis was influenced by the amount of beta-xylosidase present in the hemicellulolytic enzyme preparation. The -;xylosidase was demonstrated to play an important role in the overall conversion of heteroxylan into xylose that is analogous to the role of beta-glucosidase in the saccharification of cellulose by cellulases.
CSR Limited, Sugar Division, Sydney, 2001, NSW, Australia.
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