Real-Time Non-Invasive Monitoring of Short-Chain Fatty Acids in Exhaled Breath

Abstract

Short-chain fatty acids (SCFAs) are important metabolites produced by the gut microbiome as a result of the fermentation of non-digestible polysaccharides. The most abundant SCFAs are acetic acid, propionic acid, and butyric acid which make up 95% of this group of metabolites in the gut. Whilst conventional analysis SCFAs is done using either blood or fecal samples, SCFAs can also be detected in exhaled breath using proton transfer reaction-time-of-flight- mass spectrometry (PTR-ToF-MS) using H3O+ for ionization. However, no investigation has been performed to characterize the reactions of SCFAs with H3O+ and with other reagent ions, such as O2+ and NO+. Gas-phase samples of acetic acid, propionic acid, and butyric acid were analyzed with SRI/PTR-ToF-MS under dry and humid conditions. The ions generated and their distribution was determined for each reagent ion. It was found the humidity did not influence the product ion distribution for each SCFA. Using H3O+ as a reagent ion, SRI/PTR-ToF-MS analysis of an exhaled breath sample was performed in real-time to demonstrate the methodology. The presence of SCFAs in exhaled breath was confirmed by thermal desorption—gas chromatography—mass spectrometry (TD-GC-MS). Breath sampling repeatability was within acceptable limits (<15%) for an analytical methodology for each investigated SCFA. Nutritional intervention studies could potentially benefit from real-time monitoring of exhaled SCFAs as an alternative to measuring SCFAs invasively in blood or fecal samples since it is non-invasive, and requires minimal time investment from participants.

Chemical Analysis of Exhaled Vape Emissions: Unraveling the Complexities of Humectant Fragmentation in a Human Trial Study

“…Participants in this study walked approximately 1000 ft from the parking lot to the laboratory prior to sampling and hence this could have impacted baseline acetone levels. Other slightly elevated VOCs present in the baseline breath are also major endogenous breath metabolites. − …”

Volatile organic compounds from human skin as biomarkers of menstruation phase and severity of premenstrual syndrome: An exploratory pilot study

“…Mercaptans are metabolized in the liver, and elevated levels of mercaptans are related to halitosis and brain disease [ 38 , 39 ]. Butyric acids are one of the well-known metabolites of the gut microbiota as a result of the fermentation of non-digestible polysaccharides, and have been detected in exhaled breath [ 40 ]. Collectively, our results suggest that the menstrual cycle affects the metabolism in women, as well as the emission ratio of several compounds in skin gas.…”

Analysis of volatile short-chain fatty acids in the gas phase using secondary electrospray ionization coupled to mass spectrometry

“…Lee et al 14 optimized the operational parameters of secondary electrospray ionization (SESI) coupled to a mass spectrometer to measure volatile SCFAs in the headspace gas of gut microbial cultures. Recently, Meurs et al 15 In this article, the development, testing and integration of a dynamic vapor generator with an on-line SESI-Orbitrap mass spectrometer system was demonstrated. Test compounds included volatile C 2 to C 6 SCFAs.…”

“…Lee et al 14 optimized the operational parameters of secondary electrospray ionization (SESI) coupled to a mass spectrometer to measure volatile SCFAs in the headspace gas of gut microbial cultures. Recently, Meurs et al 15 calibrated proton transfer reaction mass spectrometry (PTR-MS) with gas standards of SCFA in the concentration range from 4 to 100 ppb and benchmarked the performance of the PTR-MS against a GC-MS obtaining satisfactory linearity and repeatability. Based on their measurements, the C 2 –C 4 SCFAs exist in the low ppb range in the human breath.…”