Medium optimization and kinetics modeling for the fermentation of hydrolyzed cheese whey permeate as a substrate for Saccharomyces cerevisiae var. boulardii

Abstract

This paper presents an efficient approach to culture medium optimization by a central composite rotatable design (CCRD) coupled to non-linear mathematical programming (NLP). This procedure was applied for the investigation regarding the growth of Saccharomyces cerevisiae var. boulardii in cheese whey permeate (CWP), which is an attractive raw material for the production of bioproducts, mainly due to its high lactose content. The tests comprehended lactose hydrolysis followed by glucose-galactose anaerobic fermentation in a batch system. A CCRD was proposed to evaluate the following factors: concentration of hydrolyzed CWP, and N, Mg and K supplementation, where the system response was considered to be cell growth. The cultivation media NLP model was empirically determined by a statistical methodology, and was also based on the elemental composition and the stoichiometry of the yeast anaerobic cultivation. The kinetic mathematical model of the yeast cultivation was proposed, where inhibition by the substrates of fast-glucose and slow-galactose metabolization, inhibition by the product ethanol, catabolite repression by glucose, and metabolic products formation were adequately considered. In addition, the response surface provided by the kinetic modeling was also analyzed. The global optimum value of biomass yield was equal to Yx/s=0.50, where the cell biomass was estimated to be 8.20gL−1 by using 40gL−1 hydrolyzed CWP.