Fermentative production of l-lactic acid from hydrolysate of wheat bran by Lactobacillus rhamnosus

Abstract

To reduce the nutrient cost of l-lactic acid production, wheat bran was chosen as a nutrient source. Various pretreatment processes were investigated, and 80 °C for 20 h by acid-hydrolysis was a suitable method considering the energy consumption. Pretreated wheat bran showed a better performance than that without treatment, especially for l-lactic acid yield (0.99 g/g). Moreover, when 25 g/l wheat bran hydrolysate was combined with 30 g/l corn steep liquor, the l-lactic acid fermentation efficiency (yield 0.99 g/g, productivity 3.75 g/l/h) was even higher than that of the control with 15 g/l yeast extract (yield 0.95 g/g, productivity 2.46 g/l/h). Although much more wheat bran hydrolysate and corn steep liquor were used than yeast extract in total amount, the cost of nitrogen in fermentation was estimated to be ¥1286/t l-lactic acid (25 g/l wheat bran hydrolysate and 30 g/l corn steep liquor), which is only 11% of the ¥11471/t l-lactic acid (15 g/l yeast extract) in control test. Therefore, nutrients of wheat bran hydrolysate and corn steep liquor could be employed to substitute yeast extract for l-lactic acid production.