Mechanism of L-malate stimulation on pediococcus cerevisiae growth

Abstract

The growth stimulation of L-malic acid added to a glucose-containing medium was conformed on six species of lactic acid forming bacteria, Pediococcus cerevisiae, Lactobacillus bulgaricus, L. acidophilus, Streptococcus lactis, S. thermophilus, and Escherichia coli. Among them P. cerevisiae was selected and the mechanism of growth stimulation by L-malic acid was studied. The stimulatory effect of L-malic acid on the growth rate of P. cerevisiae was shown only when the culture was initiated with acidic condition, particularly, it was striking around initial pH 5.0. When the culture started with low initial pH in the presence of L-malic acid, the pH level in the culture medium was found to be increased slowly reaching to a peak followed by a continuous decrease due to lactic acid produced from glucose. The temporary increase in pH was due to the conversion of added L-malic acid to L-lactic acid mediated by the action of P. cerevisiae. When the culture started with high initial pH such as above 8.0, however, no increase of culture pH and no stimulatory effect of L-malic acid were observed, under such conditions the added L-malic acid remained undegraded until the culture pH decreased. It was also found that the P. cerevisiae cells could grow best when the culture pH was controlled at 7.0 throughout the period of growth. When the pH levels of culture medium was maintained constantly, the addition of L-malic acid in the medium did not stimulate the growth of this organism. The synthesis of LDH of P. cerevisiae was not stimulated by the presence of L-malic acid. From these observations it was concluded that the presence of L-malic acid in the culture medium stimulated growth of P. cerevisiae by increasing the initial low pH to the level favorable for this organism. The increase of pH during the growth was due to the conversion of L-malic acid to L-lactic acid mediated by the activity of P. cerevisiae.