Production of Depolymerised Xylooligosaccharides Via Steam Explosion and Enzymatic Hydrolysis of Brewers’ Spent Grain

Purpose Brewers’ spent grain (BSG) is a major processing residue from the beer brewing industry, often applied for low-value animal feed or, process energy, or otherwise disposed. The processing of BSG into xylooligosaccharides (XOS), a proven prebiotic with application in the food, beverage and health industries, can be achieved through selective solubilisation/hydrolysis of its hemicellulose content. Methods In this study, the sequential processing of BSG to maximise the yield of XOS was achieved by screw-pressing to remove a protein-rich press liquid fraction, followed by steam explosion pretreatment prior to enzymatic hydrolysis of the remaining hemicellulose in the feedstock. Results A combined XOS yield of 37% (kg XOS/kg hemicellulose) was achieved from the steam explosion liquor (two-thirds) and the enzymatic hydrolysis of pretreated solids (one-third). The crude, longer-chain XOS products were subsequently depolymerised through an additional enzymatic hydrolysis step, to achieve the desired XOS molecules with degrees of polymerisation between 2 and 3, resulting in an overall XOS yield of 16%. Conclusion The overall XOS yield was increased by adding enzymatic hydrolysis of the solids fraction to the XOS production process, however, the findings of the study presented a potential trade-off between the increase in XOS yield and the cost of the increased enzyme requirements.