Lactic acid fermentation modelling of Streptococcus thermophilus YI-B1 and Lactobacillus casei  Shirota using food waste derived media

Lactic acid (LA) fermentation performances and characteristics of Streptococcus thermophilus YI-B1 and Lactobacillus casei Shirota were evaluated by the development of unstructured models including both substrate and product inhibitions on semi-defined medium. Cell growth was ceased at 300 g L−1 of glucose, 320 g L⁻¹ of fructose and 101.1 g L⁻¹ of LA for L. casei  Shirota, while in the case of S. thermophilus YI-B1 they were 180 g L⁻¹ for glucose and 49.9 g L⁻¹ for LA. An unstructured modified Monod expression was used to predict the fermentation process. The obtained R² values for the fitted models were 0.95 for L. casei Shirota and 0.80 for S. thermophilus YI-B1. Since L. casei  Shirota was more tolerant than S. thermophilus YI-B1, it was chosen for further examination in a laboratory-scale bioreactor. With the re-optimisation of a few model parameters, the unstructured models had shown a good agreement between experimental data and model simulations by using both semi-defined medium and complex media derived from food waste. Future work could further expand this dynamic model to predict fed-batch fermentation and investigate the fermentation characteristics using other carbon sources.