Lactic acid production with the supplementation of spent cells and fish wastes for the purpose of reducing impurities in fermentation broth

Taken impurities in fermentation broth into account, effect of concentration of fish waste hydrolyzate (FWH) on lactic acid production was investigated in this study. The efficiency of the fermentation using 6.8% FWH as a nutrient source was competitive to that using 1.5% yeast extract (YE), however, with a result of much higher impurities in the fermentation broth due to the much larger amount of addition of FWH. Reducing the amount of FWH reduced the amount of impurities in fermentation broth, but the fermentation efficiency dropped significantly. In order not to make fermentation efficiency drop, spent cells obtained after each fermentation were combined with FWH and their joint effect on lactic acid production was investigated. Spent cells as sole nutrient source did not show good performance in lactic acid production. Contrarily, the combination of the two nutrient sources showed complementary effect and the fermentation with the combination had much higher efficiency than that of either of the two nutrient sources. When 1.7% FWH was combined with spent cells, the fermentation efficiency was similar to that using 1.5% YE and the impurities were also in appropriate values. Finally, the feasibility of the fermentation process with the combination was determined. (C) 2007 Elsevier B.V. All rights reserved.