Lactobacillus helveticus growth and lactic acid production during pH-controlled batch cultures in whey permeate/yeast extract medium. Part I. multiple factor kinetic analysis

Abstract

Twenty pH-controlled batch cultures with Lactobacillus helveticus were carried out in whey permeate-yeast extract medium according to a composite design with three factors: pH setpoint, and yeast extract and initial whey permeate concentrations. Growth and production parameters were estimated from experimental data with the Richards and Luedeking and Piret models, respectively, and analyzed statistically with response surfaces. The maximum specific growth rate, μ max, depended primarily on pH, with an optimum of 0.7 h −1 near pH 5.5. Whey permeate concentration had no direct effect on maximum specific growth rate, but showed a strong interaction with pH. Yeast extract addition had a strong positive effect on maximum specific growth rate. During nitrogen-limited batch cultures X max depended on yeast extract concentration and pH, as well as on interactions of these variables with whey permeate concentration. The growth-associated lactic acid production parameter a was constant at 4.5 g lactic acid (g biomass) −1, while the nongrowth-associated production parameter b, estimated during growth and early stationary phase, was a linear function of pH. This study allowed for the first detailed multifactor kinetic analysis of Lb. helveticus growth and lactic acid production, with a limited number of experiments, and demonstrated the importance of interactions among tested culture conditions.