High L(+)-lactic acid productivity in continuous fermentations using bakery waste and lucerne green juice as renewable substrates

The biotechnological production of platform chemicals from renewable resources is in the scientific spotlight, as researchers seek to develop environmentally friendly and cost-efficient processes to compete with the petroleum-based ones. Lactic acid (LA) is an established platform chemical, registering an important market share, mainly owing to the increasing demand for polylactic acid. This study investigated the feasibility to produce LA from bakery waste hydrolysates and lucerne green juice (LGJ) as inexpensive substrates, using a Bacillus coagulans strain. A final LA concentration of 62.2 g/L, with a productivity of 2.59 g/(L.h) and a conversion yield of 0.57 g LA/ g bakery waste was achieved in batch fermentation mode. LA productivity reached 11.28 g/(L.h), using a continuous fermentation system coupled with cell retention membranes at a dilution rate of 0.2 h(-1). The results indicate that bakery waste hydrolysates and LGJ can be utilized for the production of highly optical pure L (+)-LA.