Effect of extraction and enzymatic esterification of ethanol on glucose consumption by two Saccharomyces cerevisiae strains: A comparative study

Extractive alcoholic fermentations of high glucose concentrations (300 and 400 g dm(-3)) using a flocculent (sake) and a non-flocculent (DER24) Saccha romyces cerevisiae strain were compared. The introduction of a Rhizomucor m iehei lipase, in the extractive fermentations of 300 g dm(-3) of glucose, i ncreased the ethanol. extraction due to its esterification with oleic acid, allowing complete glucose consumption at an organic solvent/fermentation m edium phase ratio of 1. In these conditions, an increase of ethanol yield w as observed. Total glucose consumption was also obtained in enzymatic extra ctive fermentations of 400 g dm(-3) of glucose, but only when oleic acid wa s added at the exponential growth phase. From the comparison of the extract ive fermentation performances obtained using the two yeast strains it was o bserved that the flocculent strain led to a lower glucose metabolisation ra te. This behaviour was related to the highest diffusional limitations that occur in the presence of flocs. The developed processes showed that the ass ociation of alcoholic fermentation with enzymatic extraction led to the red uction of inhibitory effects as well as to the simultaneous production of f atty esters which are compounds with several commercial applications. (C) 2 001 Society of Chemical Industry.