Estudo de condições ótimas pelo método de análise de superfície de resposta para eficiência da fermentação acética.

Abstract

The acetic fermentation is an oxidation process accomplished by a group of bacterias of the gender Acetobacter. The acetic acid produced by bacterias of this gender is the main compound of the vinegar. The production of a good vinegar depends on a series of factors as concentration of alcohol, temperature, oxygenation, pH and nutritious. This work had objective to study on bench scale, the optimum conditions of acetic acid fermentation, a process very much used in small industries of the state of Paraiba in the production of the vinegar. Initially a kinetic study of the acetic fermentation was performed with the intention of determining the influence of the variables: ethanol concentration, phosphorous concentration and concentration of nitrogen on the process in different intervals of time. For this a study with concentrations of ethanol of 2%, 4%, 6% and 8%, of phosphorous 0,05g/ml and 0,2g/ml, and of nitrogen of 0,5g/ml and 2,0g/ml, was made. Through the kinetics, it was not possible to observe conclusively the influence of the variables of the process studied. The methodology of complete factorial 23 planning was used, where the entrance variables were initial concentrations of ethanol, phosphorous and nitrogen. Tests were, accomplished with concentrations of ethanol 3%, 6% and 9%, in volume, concentrations of phosphorus 0,01 g/ml, 0,03g/ml and 0,05g/ml and concentrations of nitrogen 0,1 g/ml,0,3g/ml and 0,5g/ml. After the analyses it was necessary to elaborate another planning, enlarging the range of the variables. This time the planning was of the type 22 plus star configuration. Through the empirical mathematical models obtained and analysis of surface response it was verified that the controlled variable that presented great influence on the yield and productivity of the process was initial concentration of ethanol which has an optimum value of 4%. The nitrogen presented a discreet influence at the concentration of 1,7g/ml while the phosphorus didn't show any perceptible influence. It was also possible to observe, through the data of the variance analysis, that the empirical model observed is statistically significant.