Specificity of Amino Acid Profiles Produced in Soybean Fermentations by Three spp.

We compared the salt tolerance and proteolytic activity of 120 strains of each of , , and . Most strains exhibited growth in 12% (w/v) NaCl and showed proteolytic activity in 10% or 11% NaCl. The majority of strains grew in 14% NaCl and showed proteolytic activity in 12% or 13% NaCl. Most strains grew in 14% NaCl and exhibited proteolytic activity in 5%-7% NaCl. We selected nine representative strains of each species based on their proteolytic activities and analyzed the free amino acid (FAA) profiles produced by culture of the bacteria on soybean. Statistical analyses of the 22 FAAs quantified in the cultures revealed clustering of FAA production profiles at the species level. The FAA production profiles of and were similar, and both differed from that of . These trends persisted in cultures containing 7% NaCl. These results suggest that FAA production profiles are characteristic of each species. Specifically, in soybean cultures compared with uninoculated soybeans, increased the amounts of leucine and phenylalanine; increased the amounts of leucine, phenylalanine, and tyrosine; and increased the amounts of alanine, glutamic acid, tyrosine, and ornithine, and dramatically decreased the amount of arginine. The proteolytic activity of strains correlated with the quantity of FAAs in their soybean cultures. Considering its salt tolerance and proteolytic activity, showed high potential for contributing to the ripening of high-salt fermented soybean foods. Our results regarding the specific production of amino acids at the species level and correlations between proteolytic activities and produced amino acid quantities will facilitate the determination and selection of target strains for functional -fermented foods.