Effect of solid-state fermentation over the release of phenolic compounds from brewer's spent grain revealed by UPLC-MSE

Abstract

Brewers' spent grain (BSG) is the major by-product of the brewing industry and presents a rich chemical composition as substrate for fermentation, besides a valuable source of bioactive compounds. Solid-state fermentation (SSF) was applied using five strains of filamentous fungi in different types of BSG to evaluate the release of phenolic compounds (PC) characterized by UPLC-ESI-QTOF-MSE. Aspergillus oryzae after 3 days of fermentation was the most effective in the release of antioxidant compounds based on Folin-Ciocalteu and DPPH results. Globally, a total of 102 compounds were tentatively identified. Ferulic, p-coumaric and caffeic acids were the most abundant PC in BSG. Metabolomic approach was essential to reveal distinct PC when SSF was applied to BSG, the ratio bound to free PC was strongly reduced, probably due to the release of compounds from the lignocellulosic matrix by the fungi β-glucosidase. The malt types also significantly impacted the fermentation behavior, resulting in different phenolic profiles. Unlike the number of identifications, the total abundance was 50% reduced after fermentation, probably due to the biotransformation/degradation of hydroxycinnamic acids into their derivatives. SSF effectively increased the release of bound PC leading to a more complex and distinguished profile according to type of malt.