Alcoholic Fermentation by Yeast is Improved by Immobilization in Freeze-Dried Poly(Vinyl Alcohol) Foam

Abstract

Yeast cells were immobilized in freeze-dried poly(vinyl alcohol) (PVA) foam, and the subsequent fermentation of glucose was studied. The immobilized yeast was produced by freeze-drying a PVA solution containing dispersed yeast cells, yielding a porous foam. The prepared specimens were rigid enough to be used repeatedly in aqueous solutions for more than one week. The fermentation performance of the immobilized yeast was found to be significantly higher than that of the crude (non-immobilized) yeast. The immobilized yeast produced approximately 1.5 times more ethanol than the crude yeast. The freeze-dried PVA also appeared to protect the yeast cells against the reaction inhibition effects of ethanol. Also, the PVA foam had a considerable affinity for the yeast cells, whereas it had no significant affinity for ethanol. The kinetic constants obtained from the experimental reaction runs suggested that the improvement in the fermentation of the immobilized systems can be explained by the increase in the dissociation constant values in the Michaelis–Menten kinetic model, and that there is an optimal quantity of immobilized yeast that yields the best ethanol tolerance for this technique.