Developing a detailed kinetic model for the production of yogurt starter bacteria in single strain cultures

• A kinetic model was developed for yogurt starters’ production.
• RSM was implemented to estimate pH and temperature effects on bacterial growth.
• The model was function of pH, temperature, substrate, and product concentrations.
• The parameters were estimated with the use of particle swarm algorithm.
• The estimated parameters were validated against the experimental data.

Streptococcus thermophilus and Lactobacillus bulgaricus are the most common yogurt starter cultures used in the dairy industry. Generally, they are produced by single strain fermentation and then mixed together in appropriate proportions for the purpose of yogurt production. In the present study a kinetic model was developed for the growth and lactic acid production by these two bacteria in pH-controlled single strain batch cultures and whey based medium. The model is a function of pH, temperature, biomass, lactic acid, carbon, and nitrogen substrate concentrations. A four-parameter function was used to describe the effect of pH on the growth of each bacterium. Moreover, a modified Arrhenius law was applied in the model to describe the temperature effect. Response surface methodology was implemented to design the experiments in order to estimate the effect of pH and temperature on bacterial growth. The model was validated on a set of 12 experiments for each bacterium.