Study on acid-hydrolysis of spent cells for lactic acid fermentation

To reduce nutrient cost for lactic acid production, spent cells, a by-product in fermentation processes, were used as a nutrient source and the treatments of spent cells were investigated in this study. Untreated spent cells did not show significant effect on lactic acid production. After acid-hydrolysis, spent cells gave an increase in productivity to some extent, but the low glucose consumption indicated a nutrient limitation. The nutrient limitation was overcome easily by supplementing a small amount of yeast extract (YE). The combination of 5 g/L YE and the spent cell hydrolyzate (SCH) had high performance in lactic acid production relative to 15 g/L YE. Moreover, two kind of acid-hydrolysis methods, diluted acid based hydrolysis and concentrated acid based hydrolysis, were also compared. The diluted acid based hydrolysis had the advantages over the concentrated acid based one in lactic acid production due to its less nutrient destruction and lower salt inhibition. When diluted acid based SCH was supplemented, YE supplementation could be cut down to 20% with no significant decrease in productivity and yield.