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.

Efficient growth of Kluyveromyces marxianus biomass used as a biocatalyst in the sustainable production of ethyl acetate

“…The results refer to some problems at cultivation of K. marxianus in whey-based media; whey is poor in bioavailable nitrogen so that nitrogen can limit yeast growth [26][27][28][29]. Nitrogen-limited growth can even deregulate yeast metabolism and provoke ethanol formation at aerobic conditions [30].…”

Bioprocess Development for High Cell Mass Production of the Probiotic Yeast-Kluyveromyces lactis

“…The results that cell growth biomass did not increase significantly after increasing lactose above 60 g.L -1 can be attributed to the fact that higher lactose concentrations used in batch cultured yeasts can result in Crabtree repression which in turn inhibits the respiratory enzymes [26]. Additionally, higher lactose concentrations can lead to the osmotic inhibition of cell growth [28]. From these results, 60 g.L -1 initial lactose concentration was chosen as the optimum concentration for further cultivations.…”

Kinetic modeling of ethanol fermentation by yeast Kluyveromyces marxianus from lactose- and polyfructan- containing substrates

“…Thus, relevant parameters of Monod kinetics such as the maximum specific growth rate (µ max ), the saturation constant (K s ) and the yield of biomass (Y x/s ) can be considered as passport data for a particular organism [26]. Several kinetic models have been developed, which describe the ethanol production by different K. marxianus strains on lactose -containing substrates [27][28][29][30], including the strain DSM 5422 [12]. However, these models appear as differently structured, may contain quite distinctive parameters, as well as often disregard the possible effects of product and/or substrate inhibition [12; 27] and remain restricted by too narrow range of substrate concentrations.…”