Comparison of volatile metabolic profiles in fermented milk of Streptococcus thermophilus during the postripening period at different incubation temperatures

Streptococcus thermophilus has been extensively ap-plied in fermented milk. This study used gas chroma-tography-ion mobility spectroscopy to determine and evaluate the volatile metabolites in raw milk, milk fermented at 37 degrees C, and milk fermented at 42 degrees C. Ten discriminatory volatile metabolites were identified at different incubation temperatures: acetone, 2-hepta-none, 2-pentanone, 2-hexanone, butanal, hexanal, ethyl acetate, 3-methylbutanal, 3-methylbutanoic acid, and 2-methylpropanoic acid, indicating that fermentation temperature affected the spectrum of volatiles in milk fermented by different strains of S. thermophilus. Spe-cifically, fermentation at 37 degrees C led to accumulation of short-chain fatty acids, whereas fermentation at 42 degrees C enriched ketones and other flavor substances in the fermented milk, enhancing the flavor of the product. This work examined the differences between the vola-tile metabolites produced by different S. thermophilus strains fermented at different temperatures to evaluate the effect of temperature on the metabolic pathways.