Production of lactic acid from soybean straw using immobilized Lactobacillus casei and batch or repeated-batch fermentation

Abstract

Approximately 18 million tons of soybean straw are produced annually in China, with its disposal becoming an increasingly serious problem. Moreover, the Chinese government has banned the open burning of agricultural straw for environmental reasons. One potential solution is to use soybean straw for lactic acid (LA) production, avoiding open burning and waste. In this study, a Ca-alginate-immobilized Lactobacillus casei strain was used to produce LA from soybean straw enzymatic hydrolysate. Optimized conditions for the production of LA were initially established, consisting of Ca-alginate beads made from 2.5% sodium alginate with a diameter of 2 mm and a fermentation process using a 10% inoculum at 30 °C for 30 h. Lactic acid productivity was increased with only a slight decrease in overall yield by raising the initial sugar concentration from 8 g L-1 to 35 g L-1. Finally, immobilized cells could be reused at least 10 times without a noticeable performance decrease. These results indicated that production of LA from soybean straw enzymatic hydrolysate is a sustainable and feasible method to utilize these resources.