Non-ionic surfactant formulation sequentially enhances the enzymatic hydrolysis of cellulignin from sugarcane bagasse and the production of Monascus ruber biopigments

Critical analysis of process parameters towards smart bioreactors development in biorefinery for biorenewables production

The development of sustainable biotechnological processes is important for advancements in production of renewable chemicals, biofuels, and materials. A significant challenge is handling high biomass total solids (TS) loading, which is significant to enhance the cost-effectiveness and efficiency of biorefineries. Further, advancements in biomass pretreatment methods, such as hydrodynamic cavitation, that are employed to disrupt the complex structure of biomass, facilitating enzymatic hydrolysis and improving overall process yields, have shown promising results. Efficient pretreatment, novel enzyme evolution and hydrolysis using high TS concentration coupled with process intensification approaches i.e. simultaneous saccharification and co-fermentation (SSCF), simultaneous saccharification and fermentation (SSF), and consolidated bioprocessing (CBP) could be revolutionary in the biomass refineries. There are some key factors influencing reactor performance, such as biomass characteristics, mass transfer, enzyme characteristics, rheology, and heat transfer. These factors are critical in overcoming the challenges associated with high TS loading, including increased viscosity, microorganism selection and reduced mixing efficiency. This review highlights such critical factors when dealing with high biomass loading, by presenting strategies and reactor configurations to improve the scalability and economic viability of lignocellulosic biorefineries.

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 (We, 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.

In-depth recognition of mixed surfactants maintaining the enzymatic activity of cellulases through stabilization of their spatial structures

Mixed surfactants improve the enzymatic hydrolysis of lignocellulosic substrates by enhancing cellulase stability against heat, pH, shear, and air-liquid interface stress. Under conditions of multiple factorial stresses (50 °C, pH 4.8, 180 rpm, and 15.5 cm2 air-liquid interface), cellulase with ternary surfactants (Tween 60/Triton X-114/CTAB, the molar ratio 14:5.5:1) retained 84 % of its activity after 48 h of incubation, representing 1.15 and 1.29 folds that of the cellulase activity with the single Tween 60 and with no surfactants, respectively. This is attributed to the fact that ternary surfactants possess better rheology modulation and air-liquid interface competitiveness. In addition, the computational approach demonstrated that the ternary surfactants were capable of forming stronger hydrophobic and hydrogen-bond interactions with cellulase enzymes, thus maintaining its secondary structure and preventing the detrimental α-helix to β-sheet transformation known to compromise cellulase activity. This synergy offers valuable insights into surfactant-cellulase interactions and supports efficient enzymatic hydrolysis in biorefineries.

Surfactants, Biosurfactants, and Non-Catalytic Proteins as Key Molecules to Enhance Enzymatic Hydrolysis of Lignocellulosic Biomass

Lignocellulosic biomass (LCB) has remained a latent alternative resource to be the main substitute for oil and its derivatives in a biorefinery concept. However, its complex structure and the underdeveloped technologies for its large-scale processing keep it in a state of constant study trying to establish a consolidated process. In intensive processes, enzymes have been shown to be important molecules for the fractionation and conversion of LCB into biofuels and high-value-added molecules. However, operational challenges must be overcome before enzyme technology can be the main resource for obtaining second-generation sugars. The use of additives is shown to be a suitable strategy to improve the saccharification process. This review describes the mechanisms, roles, and effects of using additives, such as surfactants, biosurfactants, and non-catalytic proteins, separately and integrated into the enzymatic hydrolysis process of lignocellulosic biomass. In doing so, it provides a technical background in which operational biomass processing hurdles such as solids and enzymatic loadings, pretreatment burdens, and the unproductive adsorption phenomenon can be addressed.