Identity of Additional Aroma Constituents in Milk Cultures of Streptococcus lactis var. Maltigenes

Abstract

Gas chromatographic analyses of the headspace vapor over a series of milk cultures of malty and nonmalty strains of Streptococcus lactis revealed components in the malty strains tentatively identified as 2-methylpropanol and 3-methylbutanol. In a more detailed study the volatiles from milk cultures of a typical strain of S. lactis var. maltigenes were entrained and collected by an on-column trapping technique, chromatographed on l,2,3-tris(2-cyanoethoxy) propane and 1,2,4-butanetriol columns, and the separated components analyzed in a mass spectrometer. Ethanol, 2-methylpropanol, and 3-methylbutanol, as separated on both columns, were positively identified and the carbonyls including 2-methylpropanal and 3-methylbutanal were identified in the effluents from the former column.Although the culture volatiles contained more of the branched-chain alcohols than the corresponding aldehydes, organoleptic comparison of the aroma of an untreated culture with that in which the aldehydes had been removed by treatment with acidic hydroxylamine indicated that the typical malty aroma is due principally to the aldehydes.The presence of the alcohols in these cultures suggests that S. lactis var. maltigenes possesses a yeast-like alcohol dehydrogenase.