Abstract
The disposal of whey, the by-product of cheese or casein production, represents serious environmental problems. On the contrary, recovery of whey components or use of whey as fermentation medium may be advantageous not only for the environment but also for a sustainable economy. In this study we investigate the possibilities for whey fermentation with kefir grains. Firstly, optimal cultivation conditions were determined, afterwards construction of a mathematical model that describes the dynamic process of whey fermentation with kefir grains was developed. The attention was placed on maximum biomass increase, and not on the quality of the resulting kefir-like drink. Kinetic parameters were estimated and adjusted using a non-linear regression technique in order to fit with the experimental data. All experiments were performed in a laboratory batch bioreactor with whey from a commercial dairy plant. The gravimetric method was used to determine daily kefir grain increases under selected operating conditions (temperature, rotational frequency of the stirrer, and initial kefir grain mass concentration). Maximum specific growth rates of cells in whey and milk were compared. It was found that kefir grain increase was nearly the same in whey and in milk. From the obtained results, it is obvious that whey as dairy industry waste, could be effectively used in fermentation processes to obtain value added products. The estimated kinetic parameters could be used to bioreactor design.
