To establish the odor profiles of three differently fabricated commercial Swiss Tilsit cheeses, analyses were conducted using headspace solid-phase microextraction gas chromatography-mass spectrometry/pulsed flame photometric detection and gas chromatography-olfactometry to identify and quantitate volatile compounds. In addition, odor quality and the impact of target sulfur compounds on the overall odor of the cheeses were investigated. The odor profile was found to be mainly influenced by buttery-cheesy and sulfury odor notes in all cheeses. Buttery-cheesy odor notes were attributed to three main molecules: butanoic acid, 3-methylbutanoic acid, and butane-2,3-dione. Over a dozen volatile sulfur compounds were detected at parts per billion levels, but only a few influenced the odor profile of the cheeses: methanethiol, dimethyl disulfide, bis(methylthio)methane, dimethyl trisulfide, 3-(methylthio)propanal, and 2-methyltetrahydrothiophen-3-one (tentative). In conclusion, the conducted analyses allowed differentiation of the cheeses, and gas chromatography-olfactometry results confirmed that partially thermized milk cheese has a more intense and more multifaceted overall flavor.

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The characterization of volatile compounds in biological fluids offers a distinct approach to study the metabolic imprint of foods on the human metabolome, particularly to identify novel biomarkers of food intake (BFIs) that are not captured by classic metabolomics. Using a combination of dynamic headspace vacuum transfer In Trap extraction and gas chromatography coupled with mass spectrometry, we measured volatile compounds (the "volatilome") in plasma and urine samples from a randomized controlled crossover intervention study in which 11 healthy subjects ingested milk, cheese, or a soy-based drink. More than 2000 volatile compounds were detected in plasma, while 1260 compounds were detected in urine samples. A postprandial response in plasma was confirmed for 697 features. Univariate and multivariate analyses identified four molecules in plasma and 31 molecules in urine samples differentiating the ingestion of the foods, of which three metabolites in plasma and nine in urine were specific to the dairy products. Among these molecules, heptan-2one, 3,5-dimethyloctan-2-one, and undecan-2-one in plasma and 3-ethylphenol, heptan-2-one, 1-methoxy-2-propyl acetate, and 9decenoic acid were highly discriminative for dairy or cheese intake. In urine, 22 volatile compounds were highly discriminative for soy-based drink intake. The majority of these molecules have not been reported in humans. Our findings highlight the potential of plasma and urinary volatilomics for detection of novel dietary biomarkers.

This work aimed to determine the formation over time of 3-methylbutanal and 3-methylbutan-1-ol recognized as malty during the manufacture of Raclette-type cheese and the fermention of reconstituted skim milk, and filter-sterilized MRS broth. Using dynamic headspace-vacuum transfer in trap extraction followed by gas chromatography coupled with mass spectrometry− olfactometry (DHS-VTT-GC-MS-O) as a screening method for the malty compounds, five compounds (2-methylpropanal, 2-and 3methylbutanal, and 2-and 3-methylbutan-1-ol) were identified as potential compounds causing the malty aroma in starter culture development and Raclette-type cheeses. Focus on compounds having a predominant sensorial effect (3-methylbutanal and 3methylbutan-1-ol), spikings of leucine, 13 C-labeled leucine, α-ketoisocaproic acid, and α-ketoglutaric acid provided a better understanding of their formation pathway. This study highlighted the discrepancies in the formation of 3-methylbutanal and 3methylbutan-1-ol between the growth media; namely, despite the presence of free leucine available in MRS and the addition of an excess, no increase of the target compounds was observed. The concentration of these compounds in MRS increased only when αketoglutaric acid or α-ketoisocaproic acid was added, and a preference for the pathway to α-hydroxyisocaproic acid instead of 3methylbutanal was shown. In addition, a formation of 3-methylbutanal when the bacteria were not yet active was observed when spiking α-ketoisocaproic acid, which potentially indicates that this part of the metabolism could take place extracellularly. These results could potentially unveil other, not-yet-identified reactants, directly influencing the production of compounds responsible for the malty aroma in Raclette cheese.