Nutrient balance and metabolic analysis in a kluyveromyces marxianus fermentation with lactose-added whey

Abstract

Addition of lactose on whey to produce an alcoholic product by fermentation is optimized in order to maximise final ethanol concentrations and lactose consumption. The effect of the supplementation of the broth with yeast extract, ammonium sulphate, oxygen, protein, peptides and the vitamins nicotinic acid, biotin, pantothenic acid and inositol on aerobic cell growth was also studied. The Crabtree-negative yeast Kluyveromyces marxianus is employed in this study, so oxygen should enhance cell growth and reduce ethanol production. Addition of yeast extract, a source of vitamins, shifts metabolism towards fermentation. The same effect is observed when nicotinic acid and biotin are added to the medium. Individual and mixed effects of the four assayed vitamins are studied, showing that combinations of two or more vitamins diminished cell growth and lactose consumption and increased ethanol production