A comprehensive biorefinery process for valorising brewers' spent grains using conventional and deep eutectic solvents.

A holistic biorefinery concept integrating cell wall deconstruction, downstream separation and purification steps to convert brewers' spent grains (BSG) into high-value fractions was developed using alkali and deep eutectic solvents. Protein and arabinoxylan yields significantly increased with ultrasound (US) pretreatment, reaching 21% and 27% (w/w) of starting dry BSG, respectively. Protein purity reached 67% with 58% recovery efficiency, and arabinoxylans achieved 90% purity with 94% recovery efficiency using conventional sodium hydroxide (NaOH). Furthermore, the branched structure of arabinoxylans was preserved in NaOH biorefining with an arabinose/xylose ratio > 0.4. However, choline chloride maleic acid (CCM) selectively cleaved side-chain acyl substitutions, identified in phenolic fractions as 5-O-trans-p-coumaroyl-l-arabinofuranose and 5-O-trans-p-feruloyl-l-arabinofuranose. Consequently, linear monodispersed xylopyranose homopolymers and low molecular weight xylo-oligosaccharides were produced with higher phenolic yield than conventional biorefining. Holistic biorefinery concepts demonstrated the potential to extensively valorise BSG into a cascade of high-value products, promoting circular bio-economy principles through waste-to-value conversion.