Effect of pH, aeration and feeding non-sterilized agave juice in a continuous agave juice fermentation

BACKGROUND: Continuous cultures have been used since the 1950s in beer and wine fermentations due to their higher productivities compared to traditional batch systems; nevertheless, the tequila industry has not taken advantage of the possible improvements that continuous fermentations could offer. In this work, the effect of pH, aeration and feeding of non-sterilized medium, on the fermentative capability of two Saccharomyces cerevisiae strains (Si and 52) cultured in continuous fermentation, using agave juice as the fermentation medium, were studied. RESULTS: In continuous cultures, the control of the medium pH (set point at 4) did not have a significant effect on fermentation efficiency compared to fermentations in which the pH was not controlled (pH 2.5 +/- 0.3). Conversely, aeration of the cultures of both strains improved biomass production and consumption of reducing sugars and ammonium. The aeration also significantly augmented ethanol production only for Si cultures (P < 0.05). Furthermore, the feeding of medium, either sterilized or not, did not show significant differences on the production of ethanol for Si cultures. Higher concentrations of acetoin, succinic acid and diacetyl were found in the cultures fed with non-sterilized medium. CONCLUSIONS: Compared to S2, S1 has a better fermentative performance in continuous non-sterilized medium fermentations. Not controlling the pH during the cultures could prevent the possibility of microbial contamination as a result of the extreme medium acidity (pH 2.5 0.3). This work showed the possibility of scaling up agave juice continuous fermentation feeding non-sterilized medium with no control of pH. (C) 2010 Society of Chemical Industry