Sequential extraction of protein, phenolic compounds, and oligosaccharides from brewer’s spent grains

The growing global population has intensified waste generation, creating significant environmental and sustainability challenges particularly in the agri-food sector, where large volumes of residues are generated demanding efficient management and valorization. In this regard, brewer's spent grains (BSG), the main by-product of the brewing industry, offers a valuable opportunity for valorization due to its rich composition. This study presents a strategy to valorize BSG by selectively extracting protein, phenolic compounds, and oligosaccharides, which are compounds with numerous applications in the food area. To reduce energy and water costs, wet BSG was used, eliminating the need for a drying step. A sequential process combining enzymatic hydrolysis and hydrothermal treatment was performed, achieving high extraction yields for protein (65 %) and oligosaccharides (91 %). Additionally, protein extraction using alcalase enzyme in a mild alkaline medium (pH 8.5) facilitated the recovery of phenolic compounds (1.1 g GAE/100 g dry BSG). Hydrothermal treatment was highly efficient and selective to recover oligosaccharides (i.e., gluco-, xylo-, and arabino-oligosaccharides) free of impurities such as furfural, 5-hydroxymethylfurfural, and acetic acid. These findings highlight a viable approach for the selective extraction of high-purity compounds from BSG, offering a sustainable strategy for its valorization.