Lactic acid fermentation of brewer's spent grain hydrolysate byLactobacillus rhamnosuswith yeast extract addition and pH control

Lactic acid (LA) is a versatile chemical with a wide range of applications in food, pharmaceutical, cosmetic, textile and polymer industries. Brewer's spent grain (BSG) is the most abundant brewing by-product. In this study BSG hydrolysates were used for LA fermentation by Lactobacillus rhamnosus ATCC 7469. The aim of this study was to evaluate the effects of pH control during fermentation, reducing sugar content and yeast extract content in BSG hydrolysate on LA fermentation parameters. The pH control greatly increased reducing sugar utilization, l-(+)-LA content, yield and volumetric productivity. The highest l-(+)-LA yield and volumetric productivity were achieved with the reducing sugar content of 54 g/L. Yeast extract addition significantly increased reducing sugar utilization, l-(+)-LA content, L. rhamnosus cell viability, l-(+)-LA yield and volumetric productivity. The highest l-(+)-LA content (39.38 g/L), L. rhamnosus cell viability (9.67 log CFU/mL), l-(+)-LA yield (91.29%) and volumetric productivity (1.69 g/L/h) were achieved with the reducing sugar content of 54 g/L and yeast extract content of 50 g/L.