The interactive effects of enriched sources of Aspergillus ferulic acid esterase and Trichoderma xylanase on the quantitative release of hydroxycinnamic acids from oat hulls

Abstract

Oat hulls contain relatively high amounts of hydroxycinnamic acids, mainly ferulic (4-hydroxy-3-methoxycinnamic) and p-coumaric acids (4-hydroxy-cinnamic), which are inhibitory to cell wall biodegradability by rumen microorganisms. In this paper, a study of the interactive effects of enriched sources of Aspergillus ferulic acid esterase (A-FAE) and Trichoderma xylanase (T-XYL) at different levels on the quantitative release of ferulic acid and p-coumaric acid from oat hulls was carried out. The results show that relative to A-FAE alone, the combined action of A-FAE and T-XYL was superior in causing the release of ferulic acid [up to 41.0% (± 2.1%)], indicating that T-XYL is important in acting with A-FAE in the degradation of feruloyl-polysaccharides of oat hulls. There was no effect of A-FAE alone, but a significant effect of A-FAE in combination with T-XYL on the release of p-coumaric acid from oat hulls. However, there was no extensive release of p-coumaric acid [(maximum release of 9.0% (± 0.7%)] by A-FAE in the presence of T-XYL, indicating a specificity of A-FAE for feruloyl groups, which only efficiently releases ferulic acid and not p-coumaric acid from oat hulls. This study suggests that A-FAE with T-XYL has an interactive effect to be able to break the ester linkage between ferulic acid and the attached sugar, releasing a significant proportion of the ferulic acid from oat hulls. This action, which causes disruption of crosslinks, has the potential to improve hydrolysis of the remaining polysaccharides by rumen microorganisms, which, in turn, would improve rumen degradability of oat hulls. Key words: Ferulic acid esterase, oat hulls, hydroxycinnamic acids, biodegradation