Bioconversion of Dilute Acid Pretreated Corn Stover to L-Lactic Acid Using Co-Culture of Furfural Tolerant Enterococcus mundtii WX1 and Lactobacillus rhamnosus SCJ9

Abstract

This study demonstrated the bioconversion of lignocellulosic by-product corn stover (CS) to the value-added fermentative product L-lactic acid using the furfural tolerant Enterococcus mundtii WX1 and Lactobacillus rhamnosus SCJ9. The efficacy of dilute acid pretreatment by sulfuric and formic acids varying from 1% to 4% (v/v) concentration was compared. CS pretreated with 1% (v/v) sulfuric acid was selected for L-LA fermentation regarding the highest efficacy of fermentable sugar release when combined with the enzymatic hydrolysis process. Optimal conditions achieved a highest sugar release of 24.5 g/L glucose and 11.2 g/L of xylose from 100 g/L pretreated CS with 1% (v/v) sulfuric acid at 121 °C for 30 min, followed by enzymatic hydrolysis with Cellic CTec2 30 FPU/g pretreated CS at 50 °C for 48 h. The maximum L-LA titer, yield, and average productivity reached 31.4 g/L, 0.90 g/g, and 1.73 g/L/h, respectively. Moreover, addition of a hemicellulose-degrading enzyme complex combined with Cellic CTec2 led to an increase in xylose release, which resulted in a higher L-LA titer of 36.7 g/L at 48 h fermentation. Moreover, the purification of LA from culture broth by a process of electrodialysis with 331 g/L of LA and purity of 99.7% (w/w), was successful, with an optically pure L-LA of 99.9%. This study not only presents a feasible process for L-LA production from lignocellulose hydrolysate derived from abundant corn stover; this study also showed an alternative approach for solving the problem of haze air pollution caused by inappropriate management of corn production residuals.

A sustainable synthesis of polyhydroxyalkanoate from stubble waste as a carbon source using Pseudomonas putida MTCC 2475

“…Sodium hydroxide pretreatment also solubilizes and extracts lignin from lignocellulosic biomass by affecting the acetyl and ester groups, decreasing the degree of polymerization, and breaking the bonds between lignin and other carbohydrate polymers. Therefore, alkali pretreatment is an important step to increase cellulose digestibility and improve lignin solubilization ( Venturin et al, 2018 ; Klongklaew et al, 2023 ).…”

“…Alkaline delignification enhances enzymatic saccharification. According to Klongklaew et al (2023) , the pretreated cornstover yielded increased sugar as the enzyme concentration increased from 10–40 FPU/g. The maximum sugar was released when the material was treated with 40 FPU/g after pretreatment with 1% sulfuric acid.…”

Advanced Fermentation Techniques for Lactic Acid Production from Agricultural Waste

“…Klongklaew et al performed a co-culture fermentation of furfural tolerant Enterococcus mundtii (xylose-utilizing LAB) and L. rhamnosus (glucose-utilizing LAB) for LA production. The co-culture was proved to be efficient without detoxification of corn stover hydrolysate, producing 31.4 g/L of 99.9% optically pure L-LA with a yield of 0.90 g/g and productivity of 1.73 g/(L•h) [83]. Co-cultures of L. plantarum and L. paracasei showed better performance in LA fermentation from orange peel than monocultures of the same strains [84].…”

Recent Advances in the Technologies and Catalytic Processes of Ethanol Production

“…Chemical pretreatment uses a variety of chemicals such as acid and alkaline chemicals to break down the structures present in the lignocellulosic biomass at a constant ambient temperature which subsequently enhances the biomass surface availability to enzymatic hydrolysis, permitting the cellulose and hemicellulose for further conversion of fermentable sugars into biofuels [99][100][101]. The research on the bioconversion of lignocellulosic byproduct corn stover into the value-added fermentative product L-lactic acid using the furfural tolerant Enterococcus mundtii WX1 and Lactobacillus rhamnosus SCJ9 showed that corn stover pretreated with 1% (v/v) sulfuric acid was selected for L-LA fermentation and shows the highest efficacy of fermentable sugar with the optimal conditions achieved for the release of glucose and xylose at 24.5 g/L and 11.2 g/L, respectively, from 100 g/L pretreated corn stover at 121 • C for 30 min [102]. A similar result was presented by other researchers reported in the study of tobacco stem waste [103], palm kernel shell [104], sugarcane bagasse [105], and oil palm frond bagasse [106] that the dilute acid for chemical pretreatment is effective to attain high reactivity and generates protons that have a quick diffusion which substantially enhances the hydrolysis of amorphous cellulose chains and the solubilization of hemicellulose.…”