Acetaldehyde and diacetyl production by Streptococcus thermophilus and other lactic streptoccocci

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Abstract
Summary: The quantities of acetaldehyde and diacetyl produced in skim-milk and MRS media are reported for strains of Streptococcus lactis, Str. cremoris, Str. diacetilactis, Str. faecalis and Str. thermophilus obtained from culture collections or freshly isolated from natural milk cultures used in cheese manufacture. The diacetyl: acetaldehyde ratio in skim-milk medium was found to be approximately 0·1:1 for Str. lactis and Str. cremoris, 0·5:1 for Str. diacetilactis (5:1 for Str. diacetilactis PIM 13 and K.2 strains) and for Str. thermophilus 0·3:1, in skim-milk medium, and 0·8:1, in MRS medium; in the latter species cultured in MRS medium the ratio varied from 3·5:1 to 0·04:1 and when cultured in milk from 1·2:1 to 0·03:1.In both media all strains of Str. thermophilus formed more acetaldehyde and diacetyl than other homofermentative lactic streptococci.The ratio diacetyl: acetaldehyde in 9 strains of Str. diacetilactis was found to be unsuitable for a good culture flavour.