Effects of Different Neutralizing Agents on D-(-)-Lactic Acid Fermentation by <i>Escherichia coli </i>W

Abstract

Effects of NH4OH, KOH, Ca (OH) 2, CaCO3, and a mixture of CaCO3 and NH4OH as neutralizing agents for efficient recovery of lactic acid fermented by Escherichia coli W were investigated. Maximum productivities of lactic acid were 11.3 g/L, 10.7 g/L, 5.5 g/L, 11.9 g/L, and 12.8 g/L respectively. The mixed neutralizing agent of CaCO3 and NH4OH was testified to be better than any single neutralizer used in this study. CaCO3 was the most appropriate neutralizer among the first four neutralizers, which could make lactic acid precipitate in the form of calcium lactate, and facilitate the downstream separation and extraction of lactic acid. Furthermore, it was a slow type of mild neutralizer and had a limited capacity to regulate pH. NH4OH could regulate pH easily, and it was beneficial to cell growth as an additional nitrogen source, thus resulting in a relatively lower lactic acid production.