The influence of calcium-carbonate and yeast extract addition on lactic acid fermentation of brewer's spent grain hydrolysate

•Lactobacillus fermentum PL-1 produced similar L-(+)- and D-(−)-lactic acid concentrations.•Lactobacillus rhamnosus ATCC 7469 produced mostly L-(+)-lactic acid (95-98%).•Yeast extract addition increased lactic acid yield by 6-8% in L. rhamnosus fermentations.•BSG hydrolysate supplemented with yeast extract is a good substrate for lactic acid production.

Brewer's spent grain (BSG) is the major by-product of the brewing industry, representing around 85% of the total by-products generated. In this study BSG hydrolysate was produced using optimal conditions. Hydrolysates were used for lactic acid (LA) fermentation by Lactobacillus fermentum (PL-1) and Lactobacillus rhamnosus (ATCC 7469). The aim of this study was to evaluate possibilities of the BSG hydrolysate utilization as a substrate for LA fermentation. The effect of calcium-carbonate (2%) and yeast extract (0.5 to 5%) addition in hydrolysate on LA fermentation were investigated. The LA production by L. fermentum and L. rhamnosus in BSG hydrolysate was influenced by calcium-carbonate and yeast extract supplementation. L. fermentum produced a racemic mixture of L-(+)- and D-(−)-LA while L. rhamnosus produced mostly L-(+)-LA (95-98%) in all fermentations. Calcium-carbonate addition increased total LA yield by 13% in L. fermentum fermentations and by 17% in L. rhamnosus fermentations. Yeast extract addition increased total LA yield by 4-26% in L. fermentum fermentations and by 6-8% in L. rhamnosus fermentations.