Hydrolysis of Brewers' Spent Grain by Carbohydrate Degrading Enzymes

Abstract

In this work four commercial cellulase-hemicellulase mixtures with different activity profiles were used for solubilization of carbohydrates from brewers' spent grain (BSG). After the enzyme treatment, both the solubilised fraction and the unhydrolysed residue were characterized. Treatment with 5,000 nkat/g xylanase for 5 h at 50°C resulted in the solubilisation of 13-14% of the BSG dry weight as monosaccharides. This corresponded to the solubilisation of 26-28% of the original carbohydrates and 30-34% of original arabinoxylans, depending on the enzyme cocktail used. The relatively low hydrolysis level indicates that the majority of the BSG biomass is rather recalcitrant towards the cellulose-hemicellulase enzyme mixtures applied in this study. The enzyme activity profile had a crucial impact on the chemistry of the oligosaccharides produced through the solubilisation of BSG. The presence of feruloyl esterase (FAE) activity in the enzyme cocktail resulted in the production of free ferulic acid, arabinoxylo-oligosaccharides and their corresponding monomers. However, when the enzyme mixture was devoid of FAE activity, ferulic acid was still bound to the oligosaccharides. The unhydrolysed fraction was still found to contain over 40% of carbohydrates after enzymatic treatment despite the extensive enzyme dosages used. The protein fraction remained largely unaffected (i.e. insoluble) by the carbohydrate-disrupting enzyme treatments. In addition to the recalcitrant carbohydrates, the residue was enriched with lignin and lipid type structures.

Brewers' spent grain; bioactivity of phenolic component, its role in animal nutrition and potential for incorporation in functional foods: a review

“…16 % mono and dimeric phenolic acids, with 53 % of the monomeric phenolic acids accounted for by ferulic acid. The vast majority of phenolic acids were also found to be in the bound form (20) . It has been reported that following ferulic and p-coumaric acids, the next most abundant phenolic acids in BSG were found to be sinapic, caffeic and *Values expressed as % dry matter, which has been documented in two studies to be 20 .…”

Effect of extrusion conditions and hydrolysis with fiber-degrading enzymes on the production of C5 and C6 sugars from brewers’ spent grain for bioethanol production

“…Such sugar composition indicated that both cellulose and hemicellulose were present in approximately equal amounts. Forssell et al (2008) reported 45% carbohydrates and 21.5% protein in BSG. The BSG tested herein contained 41.15% carbohydrates (as sugars) and 22.77% protein.…”

“…However, they reported higher xylan and lignin contents. The composition differences could be ascribed to differences in barley genotype, harvest time, and the malting and mashing conditions employed during brewing (Mussatto et al, 2006;Forssell et al, 2008).…”

“…By using the extrusion pretreatment, the total sugars yield was improved by 14.6%. Forssell et al (2008) tested various commercial fibrolytic cocktails on BSG and achieved 28% recovery of the total sugars. Likewise, White et al (2008) treated the BSG with hot water at 121°C and after the hydrolysis with fiber-degrading enzymes achieved 184 mg total sugars g -1 .…”

“…Moreover, since BSG is rich in protein and fibers, it has been used successfully as an ingredient for production of high-fiber snacks and breads and as a feedstock for protein hydrolysis and fractionation. It has also been used for the extraction of prebiotics rich in xylo-oligosaccharides (Forssell et al, 2008). Shindo and Tachibana (2006) and White et al (2008) investigated the conversion of BSG into bioethanol with steam explosion and acid hydrolysis, respectively.…”