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

Abstract

Streptococcus thermophilus is widely used in the dairy industry to produce fermented milk. Gas chromatography-ion mobility spectrometry-based metabolomics was 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, and differences of fermentation physical properties and growth curves were also evaluated. Fermentation was completed (pH 4.60) after 6 h at 42°C and after 8 h at 37°C; there were no significant differences in viable cell counts and titratable acidity; water-holding capacity and viscosity were higher at 37°C than at 42°C. Different fermentation temperatures affected volatile metabolic profiles. After the fermentation was completed, the volatile metabolites that could be used to distinguish 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, branchedchain AA had higher levels, and leucine, isoleucine, and valine were involved in growth and metabolism, which promoted accumulation of some short-chain fatty acids such as 3-methylbutanoic acid and 2-methylpanprooic acid. At 42°C, at 3 different time points during fermentation, ethanol from glycolysis all presented higher levels, including acetone and 3-methylbutanal, producing a more pleasant flavor in the fermented milk. This work provides detailed insight into S. thermophilus fermented milk metabolites that differed between incubation temperatures; these data can be used for understanding and eventually predicting metabolic changes during milk fermentation.

Effect of different isolation sources of Lactococcus lactis subsp. lactis on volatile metabolites in fermented milk

“…Interestingly, this metabolic pathway of amino acids has been identified as crucial for strain growth ( Wang,Zhao et al, 2021 ). Metabolites of leucine, isoleucine, and valine, such as 2-methylpropionic acid, 3-methylbutyric acid, 2-methylbutyric acid, and 3-methylbutyric acid, are converted from alpha-keto-isocaproic acid ( Guo et al, 2021 ). We also analyzed 10 other important volatile metabolites, including 2,3-butanedione, acetoin, 2-nonanone, 2-undecanone, heptanal, hexanal, nonanal, 3-methylbutanal, acetic acid, 4-methyl-2-oxovaleric acid and constructed their metabolic pathway.…”

Exopolysaccharide-Producing Lacticaseibacillus rhamnosus Space Mutant Improves the Techno-Functional Characteristics of Fermented Cow and Goat Milks

“…The inoculated milks were fermented in a 37 °C constant temperature incubator. Samples were taken every 4 h until reaching the fermentation endpoint at pH 4.5 . Afterward, the fermented milks were stored at 4 °C, and samples were taken in triplicate after 1, 7, 14, and 21 days of storage.…”

Inoculum size of co-fermentative culture affects the sensory quality and volatile metabolome of fermented milk over storage

“…The pH was measured at 20°C using a FE28 pH meter. The titratable acidity (TA) was determined by titration with 0.1 mol/L NaOH using phenolphthalein as color indicator (Guo et al, 2021).…”