Differences in the Ability of Lactic Streptococci to Form Aldehydes from Certain Amino Acids

Abstract

Resting cells of five cultures of lactic streptococci were examined as to their ability to form flavorful aldehydes from four amino acids. Two strains of Streptococcus cremoris~ two strains of Streptococcus tactis, and one strain of Streptococcus lactis ear. maltigenes were incubated with isoleucine, valine, methionine, and phenylalanine, and the resulting aldehydes were isolated and identified as their 2,4-dinitrophenylhydrazones. The incubated mixtures of the amino acids and S. laetis ear. maltigenes cells were the only ones in which 2-methylbutanal~ 2-methylpropanal, ~-methylthiopropanM, and phenylacetaldehyde accumulated in sufficient quantities to allow isolation and identification of their derivatives. One of the strains of S. lactis formed trace quantities of these aldehydes; whereas, neither strain of S. cremoris, nor the freshly isolated strain of S. lactis, appeared to degrade the amino acids to aldehydes. The activity of the alpha-keto acid decarboxylase system present in some lactic streptococci and its possible role in the development of Cheddar cheese flavor are discussed.