Unveiling the mechanisms of mixed surfactant synergy in passivating lignin-cellulase interactions during lignocellulosic saccharification

Surfactants can synergistically enhance the enzymatic hydrolysis of lignocellulosic biomass, achieving higher sugar yields at lower enzyme loading. However, the exact mechanism by which mixed surfactants passivate lignin-cellulase interactions is not fully understood. This study found that the combination of ternary non-ionic and cationic surfactants (Tween 60, Triton X-114, and CTAB) significantly reduced the non-productive adsorption of lignin, with decreases of 35.4 %-55.4 % in equilibrium adsorption (W_e, 23.2 mg/g) compared to the single surfactant and the control. Meanwhile, mixed surfactants disrupted the entropy-enthalpy co-driven process for non-productive cellulase adsorption while promoting the desorption process. Non-ionic surfactants mainly contributed to reducing the hydrophobic interactions between lignin and cellulases. Positively charged CTAB enabled nonionic surfactants to form stronger H-bonds with lignin by electrophilic modification, and Triton X-114 increased van der Waals forces. Although surfactant-modified lignin exhibited lower hydrophobicity, zeta potential, and a more stable hydrogen bond network, the inhibitory effects of lignin-cellulase interactions by mixed surfactants were susceptible to lignin properties. According to the structure-activity relationship analysis (R² > 0.80), the main influencing factors included particle size, aliphatic/phenolic OH group contents, contact angle, and zeta potential of lignin. The study on the synergistic passivation of lignin-cellulase interactions by multi-component surfactant systems provides some theoretical insights for selecting and customarily designing effective additives for efficient enzymatic hydrolysis in lignocellulosic biorefineries.