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

Achieving efficient and rapid high-solids enzymatic hydrolysis for producing high titer ethanol with the assistance of di-rhamnolipids

High-solids enzymatic hydrolysis is the premise of obtaining high concentration ethanol by fermentation. In this study, corn stover was first pretreated with formic acid under mild conditions, and more than 70 % of xylan and lignin were removed within the first hour. 173.0 g/L glucose was achieved from total 30 % solid of the pretreated corn stover via fed-batch mode. Moreover, the glucose concentration rose to 194.5 g/L and the hydrolysis time was significantly reduced by 42.9 % with the addition of di-rhamnolipid. On this basis, 89.1 g/L ethanol was obtained by fermentation, and the presence of di-rhamnolipid had no negative effect on fermentation. The effective conversion of corn stover to high titer ethanol provides support for the conversion of stover to ethanol in industrial production.

Synthesis of NMN by cascade catalysis of intracellular multiple enzymes

β-Nicotinamide mononucleotide is a biologically active nucleotide compound, and its excellent anti-aging activity is widely used in medicine and has multiple functions, making NMN have broad application prospects in the fields of nutrition, health food, and even medicine. Herein, based on the supply of the co-substrate PRPP, we designed and constructed three in vivo NMN synthesis pathways using glucose, xylose, and arabinose as raw materials and Escherichia coli as the host. The best in vivo pathway through whole-cell catalysis was identified. Then, we optimized the cell culture and catalytic conditions of the optimal path to determine the optimal conditions and ultimately obtained an NMN titer of 1.8 mM.

Employing Cationic Kraft Lignin as Additive to Enhance Enzymatic Hydrolysis of Corn Stalk

A water-soluble cationic kraft lignin (named JLQKL₅₀), synthesized by combining quaternization and crosslinking reactions, was used as an additive to enhance the enzymatic hydrolysis of dilute-alkali-pretreated corn stalk. The chemical constitution of JLQKL₅₀ was investigated by Fourier transform infrared spectroscopy, ¹H nuclear magnetic resonance (NMR) and ¹³C NMR spectroscopy, and elemental analysis. The enzymatic hydrolysis efficiency of corn stalk at solid content of 10% (w/v) was significantly improved from 70.67% to 78.88% after 24 h when JLQKL₅₀ was added at a concentration of 2 g/L. Meanwhile, the enzymatic hydrolysis efficiency after 72 h reached 91.11% with 10 FPU/g of cellulase and 97.92% with 15 FPU/g of cellulase. In addition, JLQKL₅₀ was found capable of extending the pH and temperature ranges of enzymatic hydrolysis to maintain high efficiency (higher than 70%). The decrease in cellulase activity under vigorous stirring with the addition of JLQKL₅₀ was 17.4%, which was much lower than that (29.7%) without JLQKL₅₀. The addition of JLQKL₅₀ reduced the nonproductive adsorption of cellulase on the lignin substrate and improved the longevity, dispersity, and stability of the cellulase by enabling electrostatic repulsion. Therefore, the enzymatic hydrolysis of the corn stalk was enhanced. This study paves the way for the design of sustainable lignin-based additives to boost the enzymatic hydrolysis of lignocellulosic biomass.