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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.

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Brewer's spent grain (BSG) is an abundant, protein-rich coproduct from the beer industry. There is a growing interest in increasing and diversifying the exploitation of BSG and related coproducts for economic and environmental reasons. In this paper, we report on a study of the solubilization of proteinaceous material from BSG using several commercial peptidase preparations. Our data show that Alcalase is the most effective peptidase for solubilization of BSG proteins, with an ability to release up to 77% of total protein. The peptides produced by Alcalase had lower average molecular weight than peptides produced by the less effective enzymes. Processes that combined peptidase treatment with carbohydrate-degrading enzyme preparations such as Depol740 increased the solubilization of dry matter (from 30 to 43% under optimal conditions). However, such additional treatment had little effect on the solubilization of protein. The choice of enzyme dosage depends on the desired hydrolysis time and was assessed through several experiments. Protein solubilization was consistently better at pH 8.0 as compared to pH 6.8. Maximum protein solubilization at pH 8.0 within 4 h required the use of 10-20 microL Alcalase per g of dry matter. However, a considerable degree of solubilization (64%) and hydrolysates with high protein content could be obtained using doses down to only 1.2 microL. Amino acid composition analyses showed that Alcalase treatment solubilizes proline and glutamine (constituents of barley hordein) slightly more efficiently than the other amino acids in BSG.