Enhancing the biorefinery of brewery spent grain by deep eutectic solvent pretreatment: Optimisation of polysaccharide enrichment through a response surface methodology

One of the main challenges in biorefinery is the efficient fractionation and use of lignocellulosic biomass. In this sense, pretreatment with deep eutectic solvents (DES) is highlighted as a clean and effective separation method, due to its selective solubilisation of hemicellulose and lignin fractions while preserving cellulose. This study presents a process of the enrichment of polysaccharide content and the improvement of enzymatic digestibility using choline chloride (ChCl) and lactic acid (LA) or glycerol (Gly) in brewery spent grain (BSG) pretreatment. Additionally, it describes how improvements can be made in obtaining polysaccharide-rich material through a response surface methodology, this by means of analysing the operational conditions (temperature, reaction time, and molar ratio) using ChCl:LA. The optimised operational conditions (130 °C, 90 min, and 1:8 mol/mol) generate a 75 % enrichment of polysaccharide fraction and the removal of 77.13 %, 50.70 %, and 100 % of acid-soluble lignin, xylan, and arabinan, respectively. Moreover, the process enhances the saccharification of glucan and xylan to almost 70 % using Cellic CTec2, and to 80 % of glucan and 40 % of xylan using A. niger CECT 2700 enzymatic extract. This constitutes a promising approach to the fractioning of cellulose and lignin from BSG through DES pretreatment, which is unfeasible using traditional pretreatment methods.