title: Vicinal diketone formation in yogurt: (13)C precursors and effect of branched-chain amino acids.
abstract: Addition of branched-chain amino acids (BCAA) or an inhibitor of the BCAA biochemical pathways during fermentation of milk with a lac(-) mutant of Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus strongly influenced the formation of two aroma-impact compounds, 2,3-butanedione and 2,3-pentanedione, as well as their direct precursors 2-acetolactate and 2-acetohydroxybutyrate. This suggests a connection between vicinal diketone formation and BCAA biosynthesis in yogurt bacteria. A recently developed static-and-trapped headspace technique combined with gas chromatography-mass spectrometry demonstrated incorporation of (13)C from [U-(13)C(6)]-D-glucose and [U-(13)C(4)]-L-threonine into both vicinal diketones. For 2,3-butanedione, glucose is the major precursor via pyruvate and activated acetaldehyde. For 2, 3-pentanedione, L-threonine is a precursor via 2-ketobutyrate, but glucose is the major contributor via activated acetaldehyde and, possibly, also via 2-ketobutyrate, which is a degradation product of 3-methylaspartate, an intermediate in glutamate synthesis.
authors.affiliation: Nestlé Research Center, NESTEC Ltd., P.O. Box 44, Vers-chez-les-Blanc, 1000 Lausanne 26, Switzerland.
authors.forename: A
authors.initials: A
authors.lastname: Ott
authors.forename: J E
authors.initials: JE
authors.lastname: Germond
authors.forename: A
authors.initials: A
authors.lastname: Chaintreau
mesh_terms: D000597:Amino Acids, Branched-Chain / Q000096:biosynthesis*; D002247:Carbon Isotopes; D003931:Diacetyl / Q000737:chemistry*; D005285:Fermentation; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D007778:Lactobacillus / Q000378:metabolism; D009812:Odorants; D010422:Pentanones / Q000737:chemistry*; D013291:Streptococcus / Q000378:metabolism; D015014:Yogurt / Q000032:analysis*
chemical_list: D000597:Amino Acids, Branched-Chain; D002247:Carbon Isotopes; D010422:Pentanones; D003931:Diacetyl; C013186:2,3-pentanedione