Bioconversion effects of brewer's spent grain with L. pentosus on lactic and phenolic acids

In this thesis we were investigated the effects of brewer's spent grain biotransformation by L.pentosus strains on lactic and phenolic acids. At the beginning, brewing spent grain was diluted with 1,25% H₂SO₄ (1:8 g / g) solid/liquid ratio for hydrolysis of complex compounds. The bioconversion was performed by different strains of L.pentosus as Lactobacillus pentosus O157, Lactobacillus pentosus O18, Lactobacillus pentosus O19. Fermentation conditions were determined as: pH 6.0; follow up to 96 hourst/ 31 ° C and %20 xylose concentrations. The highest amount of lactic acid (22.4 g/L) was determined to be produced by Lactobacillus pentosus O18 at the second day of fermentation with highest yield value of % 13.80. In the second part of the study, during bioconversion of brewer's spent grain by Lactobacillus pentosus O18 were used different nitrogen sources (yeast extract, corn steep water, peptone, urea, tryptone). Used nitrogen sources quantities were determined on the basis of equivalent nitrogen 10 g/L of yeast extract. Values obtained at each 12th hour of fermentation were evaluated by HPLC technique. The best results for gallic acid, coumaric acid, ferulic acid, benzoic acid, vanillic acid and sinapic acid were obtained with yeast extract and peptone nitrogen sources. The maximum increases were detected for hydroxycinnamic acids ferulic (60-175 mg / L) and p-coumaric acid (100 to 322.5 mg / L).