The effect of acetyl structure optimization of spruce (Picea abies.) mannan on promoting enzymatic hydrolysis

In spruce, hemicelluloses containing acetyl groups hinder cellulase accessibility to cellulose, which reduces hydrolysis efficiency. This study investigated the effect of acetylation on cellulose hydrolysis. With an addition of 2-8 mg/mL, natural spruce galactoglucomannan (GGM) exhibited inhibition rates of 17.66 %-26.64 % on cellulose hydrolysis. Deacetylated galactoglucomannan (DGM) further intensified hydrolysis inhibition, reaching up to 41.95 % at 8 mg/mL. Conversely, the addition of 2 mg/mL of highly acetylated galactoglucomannan (AGM) significantly alleviated hydrolysis inhibition, thereby reducing inhibition by 76.44 %. The inhibition effect of acetylation on cellulose hydrolysis was directly proportional to AGM amount and inversely proportional to hydrolysis time, as confirmed by cellulose adsorption experiments. Infrared spectroscopy and nuclear magnetic resonance spectroscopy revealed structural changes in GGM due to acetylation and deacetylation. The effect of mannan on cellulase activity was examined via fluorescence spectroscopy. Steric hindrance and electrostatic repulsion from acetyl groups on mannan reduced enzyme adsorption. Highly acetylated mannose enhanced cellulase stability. These findings provide new insights for biorefining applications in spruce.