Production of Volatile Fatty Acids by Some Lactic Acid Bacteria. II. Selective Formation of Volatile FattyAcids by Degradation of Amino Acids

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Abstract
The kinds and amounts of volatile fatty-acids (VFA) produced from single amino-acids, modified amino-acid mixtures and pyruvate by resting cells of some streptococci and lactobacilli were investigated. The effects of pH of substrate, temperature of incubation and O2 removal from substrate on VFA production from some selected amino-acids were studied. Two strains of lactic-acid bacteria (S. diacetilactis DRCl and Lactobacillus No.-138) produced acetate from alanine, glycin or serine, propionate from threonine, isobutyrate from valine and isovalerate or a valerate from leucine and isoleucine. These reactions are mainly due to oxidative deamination and decarboxylation. Optimum pH was at neutral or slightly alkaline range, and optimum temperature was 32[degree]C for streptococci and 42% for lactobacilli. The removal of O2 from substrate changed the total and individual VFA produced from certain amino-acids, although there was no reductive deamination. The VFA patterns from amino-acid mixtures depended upon a qualitative and quantitative balance of the amino-acids. Acetate was produced from pyruvate by strains-DRCl and No.-138. Some possible explanations of the mechanism of individual VFA production from amino-acids are discussed.