Mono- and dimeric ferulic acid release from brewer's spent grain by fungal feruloyl esterases

Ultraflo L, a beta-glucanase preparation from Humicola insolens sold for reducing viscosity problems in the brewing industry, exhibited activity against the methyl esters of ferulic, caffeic, p-coumaric and sinapic acids, displaying mainly type-B feruloyl esterase activity. Ultraflo also contained the ability to release 65% of the available ferulic acid (FA) together with three forms of diferulate from brewer's spent grain (BSG). An "esterase-free" Ultraflo preparation greatly enhanced the ability of a feruloyl esterase from Aspergillus niger, AnFAEA, to release FA (from 23 to 47%) and its dimeric forms, especially the 8,5' benzofuran form, from BSG. While total release of these phenolic acids was not observed, this synergistic enhancement of ferulate release demonstrates that FA and its dimeric forms present in BSG require the addition of more than a xylanase. This suggests either that FA is not solely attached to arabinoxylan in the barley cell wall, or that the cell wall polysaccharides in BSG hinder the accessibility of enzymes to the ferulates, due to processing treatments.