Diversion of the Lactic Acid Fermentation with Oxidized Substrate

Abstract

By using an oxidized substrate and shifting the reaction during growth to an alkaline pH, it is possible to eliminate lactic acid as a fermentation product of certain homofermentative lactic acid bacteria. Therefore, the lactic acid fermentation is not essential to the reactions yielding energy for the growth of these organisms. The products of fermentation of citric acid at pH 8.5 are 1 mole each of CO2 and formic acid and 2 moles of acetic acid. At an acid reaction, acetylmethylcarbinol is formed and lactic acid becomes an important product of citric acid fermentation. These changes are accompanied by an increase in CO2 which parallels the increase in lactic acid plus acetylmethylcar-binol. A corresponding decrease in the yield of formic and acetic acids occurs. Cell suspensions harvested from a citrate-containing medium yield approx. the same products as do growing cultures. With resting cells, pyruvic acid accumulates at an alkaline reaction. The results indicate the presence of several enzymes similar to those present in other types of organisms.