Metabolic footprint analysis of volatile metabolites by gas chromatographyion mobility spectrometry to discriminate between different fermentation temperatures during Streptococcus thermophilus milk fermentation

摘要

Streptococcus thermophilus is widely used in the dairyindustry to produce fermented milk. Gas chromatography-ion mobility spectrometry–based metabolomicswas used to discriminate different fermentation temperatures(37°C and 42°C) at 3 time points (F0: pH= 6.50 ± 0.02; F1: pH = 5.20 ± 0.02; F2: pH = 4.60± 0.02) during S. thermophilus milk fermentation, anddifferences of fermentation physical properties andgrowth curves were also evaluated. Fermentation wascompleted (pH 4.60) after 6 h at 42°C and after 8 hat 37°C; there were no significant differences in viablecell counts and titratable acidity; water-holding capacityand viscosity were higher at 37°C than at 42°C.Different fermentation temperatures affected volatilemetabolic profiles. After the fermentation was completed,the volatile metabolites that could be used todistinguish the fermentation temperature were hexanal,butyraldehyde, ethyl acetate, ethanol, 3-methylbutanal,3-methylbutanoic acid, and 2-methylpropionic acid.Specifically, at 37°C of milk fermentation, branchedchainAA had higher levels, and leucine, isoleucine, andvaline were involved in growth and metabolism, whichpromoted accumulation of some short-chain fatty acidssuch as 3-methylbutanoic acid and 2-methylpanprooicacid. At 42°C, at 3 different time points during fermentation,ethanol from glycolysis all presented higher levels,including acetone and 3-methylbutanal, producinga more pleasant flavor in the fermented milk. This workprovides detailed insight into S. thermophilus fermentedmilk metabolites that differed between incubation temperatures;these data can be used for understandingand eventually predicting metabolic changes duringmilk fermentation.