Overcoming the lignin barrier in Brewer’s spent grain: synergistic effect of additives on enzymatic hydrolysis

Abstract

Brewer’s spent grain (BSG), an abundant lignocellulosic byproduct, has significant potential for biofuel and biochemical production, but its recalcitrant structure, particularly lignin, hinders enzymatic hydrolysis. This study evaluated the effect of additives on the enzymatic hydrolysis of Ca(OH)2 pretreated brewery residue to improve cellulose accessibility and glucose recovery. Nine additives were initially tested, of which PEG 6000, Tween 80, and a cationic polymer improved hydrolysis yield. Response Surface Methodology (RSM) with Central Composite Design (CCD) was applied to optimize additive concentrations. The synergistic use of PEG 6000 and the cationic polymer achieved up to 87.9% glucose recovery with high model reliability (R2 = 94%). The optimized conditions increased glucose release at different solid loadings, with improvements of 34.35%, 30.4%, and 15.7% for 5%, 10%, and 15% solids, respectively. While higher polymer concentrations showed some yeast inhibition, PEG 6000 exhibited no adverse fermentation effects. These findings demonstrate that the synergistic application of PEG 6000 and a cationic polymer effectively mitigates lignin barriers, increases the efficiency of enzymatic hydrolysis, and supports the sustainable valorization of BSG into fermentable sugars for bioeconomy applications.