The effect of fatty acids on the metabolism of pyruvate in lactic acid streptococci

Abstract

SummaryThe metabolism, of pyruvate by resting whole-cell suspensions of Group N streptococci was studied over the pH range 4·0–7·0, in the presence and absence of oleic acid. In the absence of oleic acid pyruvate was utilized maximally at pH 4·5 with the formation of acetate (volatile acid), acetoin + diacetyl and carbon dioxide. The formation of acetate took precedence over the formation of acetoin + diacetyl. In the presenoe of oleic acid the utilization of pyruvate was maximal at pH 6·5 and completely inhibited at pH 4·5. The only products detected at pH 6·5 were acetoin + diacetyl and carbon dioxide. This effect of oleic acid on the metabolism of pyruvate was also obtained after treating the cells with acetone. The mechanism of action of oleic acid on cells of Group N streptococci and its possible influence on the formation of flavour compounds in cultured dairy products is discussed.