Formulation of Fish Waste as a Low-Cost Fermentative Nutrient for Lactic Acid Production by Lactobacillus pentosus

Purpose The formulation of yeast extract and fish waste was developed as an alternative nutrient source for lactic acid fermentation to reduce the cost of nutrient input and to minimize the impurities brought in by fish waste. Method The formulation of fish waste with the supplement of small amounts of yeast extract was studied. Three levels of fish waste (10, 15, and 30 g/L) were investigated with 1–5 g/L yeast extract for the lactic acid fermentation using 100 g/L glucose as substrate. Results The microbial fermentation process for lactic acid requires certain types and amounts of nutrient. Our previous studies showed that fish waste could be used as an inexpensive nutrient source for lactic acid bacteria, but a relatively high dosage of fish waste is needed. The introduction of high loading of fish waste brought in impurities which complicated the downstream processing. In this study, satisfactory results were obtained with the optimal formulation of 10 g/L fish waste + 5 g/L YE, which gave 99.5% lactic acid yield with a productivity of 2.764 g/L/h. Experimental data showed good fitness to an empirical kinetic model with regression coefficient (r 2 ) in the range of 0.931 to 0.997. Conclusion Compared to using either yeast extract or fish waste as nutrient alone, optimal formulation significantly lowered the lactic acid fermentation cost and impurity input. A simplified kinetic model based on product availability adequately reflected substrate consumption and product production with a high degree of fidelity (r 2 > 0.93). Graphical Abstract