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

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 have been investigated. The effects of pit of substrate, temperature of incubation, and oxygen removal from substrate on VFA production from some selected amino acids were also studied. Two strains of lactic acid bacteria, S. diacetilactis DRC1 and Lactobacillus No. 138, produced acetate from alanine, glycine, or serine, propionate from threonine, isobutyrate from valine, and isovalerate or a valerate from leucine and isoleucine. These reactions may be ascribed mainly to oxidative deamination and decarboxylation. Optimum pH was at neutral or slightly alkaline range, and optimum temperature was 32 C for streptococci and 42 C for lactobacilli. The removal of oxygen from substrate brought about some changes of 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 production from pyruvate by strains DRC1 and No. 138 was also found. Some possible explanations of the mechanism of individual VFA production from amino acids are discussed.