Brewing and malting technology by-products as raw materials in L-(+)-lactic acid fermentation

Abstract

BACKGROUND Brewer's spent grain (BSG), brewer's yeast (BY), malt rootlets (MR), and soy lecithin (SL) are valuable and abundant by-products obtained from brewing, malting, and oil industry, respectively. L-(+)-lactic acid (LA) is organic acid that has a wide range of application. In this study hydrolysate obtained from BSG and MR mixture (BSGMR), was used in combination with SL and BY extract (BYE) in LA fermentation. The aim was to evaluate the effect and to optimize the addition of SL (0.1% and 0.2%) or BYE (10% and 20%) compared with Tween 80 (0.1%) and yeast extract (0.8%), in batch and fed-batch LA fermentation. RESULTS Using optimal SL and BYE concentrations (0.19% and 19.12%, respectively) obtained by response surface methodology (RSM), the highest LA concentration, yield, and volumetric productivity of 28.43 g L-1, 93.03%, and 1.04 g L-1 h(-1), respectively, were achieved in batch fermentation, with further increase using fed-batch fermentation (70.17 g L-1, 94.57%, and 1.22 g L-1 h(-1), respectively). CONCLUSION The results achieved indicated that the combination of industrial by-products, BSG, MR, SL, and BYE can be used as very suitable fermentation media for LA production, and that SL and BYE could be used as cheap replacements for Tween 80 and YE without decreasing fermentation efficiency.