PRODUCTION OF LACTIC ACID FROM BREWER’S SPENT GRAIN BY USING DIFFERENT NITROGEN SOURCES AND DIFFERENT LACTOBACILLUS PENTOSUS STRAINS

Brewer's spent grain (BSG), which is released as a by-product from brewing process, has attracted the attention of scientific research as a low-cost raw material for biotechnological applications. In this study, BSG was used as fermentation medium for production of lactic acid by using different Lb. pentosus strains (Lactobacillus pentosus O157, Lactobacillus pentosus O18, Lactobacillus pentosus O19). Initially, BSG was diluted with 1.25% of H₂SO₄, a solid/liquid ratio (1:8 g/g) for hydrolysis of the medium containing hemicellulose sugars. Lactic acid production conditions by using Lactobacillus pentosus strains were optimized as: pH 6.0, 96 hours at 31°C and 20.0 % of xylose concentration. The maximum amount and yield for lactic acid (22.4 g/L; 13.80 %) was produced with a strain of Lactobacillus pentosus O18, respectively.  In the second part of the study, different nitrogen sources (yeast extract, corn steep water, peptone, urea and tryptone) were used for production of lactic acid by using Lactobacillus pentosus O18 strain. In order to meet the complex organic matter needs of lactic acid bacteria, different nitrogen sources were calculated on the basis of equivalent nitrogen (10 g/L of yeast extract) amount. Among used sources the highest yield was obtained with yeast extract followed by peptone.