Optimization of enzymatic hydrolysis and fermentation of rice husk for lactic acid production

Abstract

Lactic acid is an industrially important compound due to its versatility in the food, pharmaceutical, and chemical sectors. This study addresses the valorization of rice husk through an integrated process involving sequential autohydrolyzed and alkaline pretreatment, followed by enzymatic hydrolysis and lactic acid fermentation. The effects of solids loading, enzyme dosage, and pH were evaluated using a Box–Behnken experimental design, achieving glucose concentrations of up to 130 g/L. Considering the inhibitory effects observed at high sugar concentrations during fermentation, the hydrolysate was diluted to 40 g/L glucose for subsequent processing. The resulting hydrolysate was fermented by Heyndrickxia coagulans DSM 2314 under anaerobic conditions at 50 °C and pH 7.0, reaching a lactic acid concentration of 30.8 g/L after 24 h. The results demonstrate the effectiveness of the process for producing high concentrations of fermentable sugars and their rapid conversion into lactic acid, highlighting its potential for the scalable valorization of lignocellulosic residues.