LAUSR

Abstract 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.