Otimização da produção do ácido láctico através da fermentação do soro de queijo por Lactobacillus helveticus
In this work the homolactic fermentation of cheese whey using Lactobacillushelveticus (ATCC 15009) was studied. The experiments were carried out in a batch reactor,with agitation, temperature and pH control during a period of 32 hours. The influences of fourvariables according to a composite design on the production of lactic acid were analyzed:temperature, pH, concentration of lactose and concentration of yeast extract, used as asupplement for the fermentation medium. The effects of these variables and its interactionswere analyzed by the response surface methodology. The biggest influences were exerted bypH and by the concentration of yeast extract. Through a canonic analysis of the adjustedresponse surface, the optimal variables values that led to the biggest production of lactic acidwere determined: 82 g/L of lactose, 23.36 g/L of yeast extract at 40 ºC and pH 6.8. In theseconditions, the concentration of the lactic acid reached 59 g/L. Through a kinetic study, it wasproved that the homolactic fermentation of whey is inhibited by the substrate as well as by theproduct. Models were tested to describe the microbial growth, the substrate consumption andthe product formation. The logistic equation represented well the growth of the Lactobacillushelveticus. The biggest deviations occurred at the beginning of the fermentation and at thestationary phase, where the condition of instantaneous rate of growth equal to zero is notpredicted by the model. The measures of bias from Box and of curvature from Bates andWatts referring to this model demonstrated that there is a statistic confidence for the leastsquare estimators of the parameters. The adjustment of the growth model from Amrane(1999) for the experimental data was slightly better than the one obtained from the logisticequation. However, the measures of bias from Box and of curvature from Bates and Wattsdemonstrated that the statistical inferences on the parameters estimative are not valid.Therefore, the possibility of using this model was discarded. The models of substrateconsumption from Pirt and of formation of product from Luedeking and Piret fitted well to theexperimental data.
Advisor:Marcos Antonio de Souza Barrozo; Luis Alexandre Pedro de Freitas; Euclídes Honório de Araújo; João Jorge Ribeiro Damasceno; Jonas Contiero; Eloizio Julio Ribeiro
School:Universidade Federal de Uberlândia
Source Type:Master's Thesis
Keywords:Lactobacillus helveticus Whey Lactic acid Optimization
Date of Publication:08/30/2006