Influência conjunta do pH, temperatura e concentração de sulfito na fermentação alcoólica de mostos de sacarose

Abstract

This work presents as objective to study the simultaneous influence of pH, temperature and sulphite concentration on situations comprising stress situations for the yeast on the alcoholic fermentation by the use of a central composite design (CCD). The yeast Saccharomyces cerevisiae Y-940 was used and the experiments were carried out in a temperature and agitation controlled mixture reactor with a useful volume of 2L. The conditions defined on the CCD were: temperature ranging from 21.5 to 48.5ºC, pH ranging from 1.5 to 5.5 and sulphite concentration ranging from 0 to 345mg/L. The fermentations were accompanied throughout time by sucrose, ethanol, glycerol and cells concentrations and, by the end of 12 hours, cell viability and trehalose concentration were determined as well. From the obtained data, cell viability, the final amount of intracellular trehalose, ethanol yield and productivity and glycerol yield were analyzed as responses. The variables values that maximized the cell viability were temperature ranging from 21.5 to 31ºC, pH ranging from 3.2 to 4.2 and sulphite concentration from 0 to 45mg/L. For the final amount of trehalose, the temperature interval that maximized the response ranged from 23.5 to 38ºC, the pH ranging from 3.5 to 4.6 and the sulphite concentration ranging from 0 to 90mg/L. To achieve the maximum ethanol yield (g/g), the temperature ranged from 32.5 to 39ºC, the pH ranged from 3.5 to 4.3 and the sulphite concentration from 0 to 90 mg/L. The ethanol maximum productivity (g/L.h) was attained in a temperature of 33.5ºC, in a pH of 3.9 and in absence of sulphite. The conditions for a maximum glycerol yield were: 48.5ºC, pH of 5.5 and a sulphite concentration of 345 mg/L. With the objective of investigating the sulphite effect on fermentation with a greater level of detail, additional experiments were conducted by adopting conditions that allowed to evaluate the isolated effect of sulphite on fermentations, allowing to reach the conclusion that greater sulphite concentrations generates a high glycerol yield and lowers ethanol productivity and cell viability. The fermentation kinetic at the point defined as optimal by analyzing the CCD responses was well adjusted to the model proposed by Ghose and Thiagy. The found μmax parameter was 0,15h-1, Ks of 3,31g/L, Ki of 135,87g/L and a Pm of 84,23g/L.