The balance of gut microbial communities has been proven to have a high correlation with human health and disease. Non-digestible carbohydrates unable to be degraded by human digestive enzymes can be utilized by the gut microbiome and thus impact gut microbial ecology. Short-chain fatty acids (SCFAs), as the major metabolic products of fermentation by gut microbes, are key mediators and biomarkers toward chronic, intestinal diseases. However, the molecular properties of SCFAs and the complexity of polysaccharides make the task of linking dietary carbohydrate structure to predictable SCFAs production difficult. Therefore, in this study, we introduce a rapid-throughput liquid-chromatography mass spectrometry-based method to perform absolute quantification of gut microbiome-derived SCFAs and other carboxylic acid metabolites. Coupled with the robust glycomic analysis platforms established in our lab before, we were able to understand the structure of dietary carbohydrates and the corresponding outcome of SCFAs. We then applied these platforms to the fermentation products from 56 common fruits and vegetables in an <i>in vitro </i>fecal bioreactor model. The result shows that the SCFAs production profile differs between dietary carbohydrates after fermentation by feces bioreactors. For example, cucumber has significantly higher propionic (4.4 mg/ml) and butyric acid (13 mg/ml) concentrations in the fermented product compared to the kidney beans at day 3, which only has propionic acid level of 0.28 mg/ml and butyric acid level of 0.24 mg/ml. Linking this discovery to the carbohydrates information, a higher content of galactose (0.044 g/g), xylose (0.033 g/g) and galacturonic acid (0.038 g/g) was found in cucumber than in kidney bean (galactose 0.019 g/g, xylose 0.010 g/g and galacturonic acid 0.004 g/g) which could possibly lead to the high propionic acid and butyric acid productions. In brief, these methods will provide new insight toward understanding human nutrition, food-microbiome interactions, and their impact on human health.

Deciphering the relationship between gut microbe-derived SCFAs and dietary carbohydrates using LC-MS based platforms

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ACS Fall 2022

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