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.