ACTION OF TRICHODERMA-REESEI AND ASPERGILLUS-ORYZAE ESTERASES IN THE DEACETYLATION OF HEMICELLULOSES

Xylans and mannans contain different esterified substituents such as a cetyl, feruloyl and p-coumaroyl side groups, The functions of hemicell ulose-deacetylating esterases of Trichoderma reesei and Aspergillus or yzae are discussed in this paper, Both fungi produce multiple esterase s and two different esterases were isolated from both T. reesei and A, oryzae, The enzymes differed significantly in their substrate specifi cities, Acetyl xylan esterase of T. reesei was highly active on polyme ric xylan but was unable to remove acetyl substituents from glucomanna n or phenolic substituents from wheat straw arabinoxylan, Another este rase, acetyl esterase from T. reesei, had activity only towards short oligomeric and monomeric acetates derived both from xylan and glucoman nan, The acetyl glucomannan esterase of A. oryzae was most active towa rds polymeric glucomannan, but was also able to remove acetyl groups f rom xylan, The only esterase studied which was active against phenolic substituents in arabinoxylans was the feruloyl esterase from A, oryza e, Feruloyl esterase had the widest substrate specificity of the ester ases studied, It was also able to act on acetyl groups both in xylan a nd in glucomannan, The simultaneous enzymic liberation of acetyl group s from xylan and glucomannan clearly enhanced the action of xylan- and mannan-degrading enzymes, thus increasing the hydrolysis yield signif icantly, However, none of the esterases was able to remove all acetyl substituents when acting alone and simultaneous action of two esterase s was needed for complete deacetylation.