Abstract
Analysis of variance was used to evaluate the simultaneous effects of strain, incubation temperature (15 to 25 degrees C), agitation time (0 to 24 h), and initial sulfite concentration (100 to 300 ppm) on glycerol production in grape juice by Saccharomyces cerevisiae. Fourteen strains were studied to determine their growth patterns in the presence of sulfites and ethanol. Baker's yeast strains were more sensitive to sulfite than wine strains, and little growth occurred at initial sulfite levels greater than 150 ppm. Sensitivity to sulfite increased with increasing levels of ethanol. Three strains exhibiting the best growth in the presence of sulfites and ethanol were selected for interaction studies. Fermentations were carried out until the solids content had decreased to less than 6 degrees Brix, which was the point that glycerol content became stable. For the three strains used, the greatest level of glycerol production was observed in the presence of 300 ppm of sulfite for most incubation temperatures and agitation times. There was significant interaction between the strain, incubation temperature, and agitation time parameters for glycerol synthesis, and a response surface method was used to predict the optimal conditions for glycerol production. Under static conditions, the highest level of glycerol production was observed at 20 degrees C, while incubation at 25 degrees C gave the best results when the cultures were agitated for 24 h. Response surface equations were used to predict that the optimum conditions for glycerol production by S. cerevisiae Y11 were a temperature of 22 degrees C, an initial sulfite concentration of 300 ppm, and no agitation, which yielded 0.68 g of glycerol per 100 ml.
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