Modulation of the Gut Microbiota by Tart Cherries Consumption: In vitro and Human Dietary Intervention Studies

Introduction: Dietary polyphenols have long been considered beneficial, but these health claims have mainly been based on the properties of the native polyphenols. However, the vast majority of plant/fruit polyphenols molecules are too big to be directly absorbed in the small intestine. It is becoming increasingly evident that dietary polyphenols are converted to smaller metabolites by the resident microbiota, mainly in the colon. Therefore, understanding both how the gut microbiota is affected by polyphenol consumption and the fate of said polyphenols is crucial to solidify health claims. Tart cherries have been shown to exert health benefits, and this has been attributed to their specific and abundant polyphenolic content.

Purpose: The aim of this study was to conduct preliminary studies in vitro and in vivo to assess the potential prebiotic effect of concentrate tart cherries juice.

Methods: Tart cherry juice concentrates, as well as representative polyphenol extracts, was used to set up in vitro assays (fecal slurries, simulator of the human intestinal tract microbial ecology) from which fecal samples were obtained and subjected to 16S rRNA gene sequence high throughput sequencing (MiSeq) and metabolomics through HPLC-qTOF-MS. A short-term dietary intervention study was conducted with 10 participants consuming the recommended amount of tart cherry juice daily over five days. Fecal samples were taken before and after the dietary intervention and subjected 16S rRNA gene sequence high throughput sequencing

Results: In the in vitro study, both tart cherry juices and chlorogenic acid (the main polyphenolic constituent of the juices) resulted in a significant increase of Lactobacillus and Bifidobacterium, correlating with an increase in Ruminococcus. The metabolomics indicated that, in contrast with sweet cherry juice, tart cherries polyphenols where predominantly converted to coumaric acid. A very recent indepedent study supported those microbiota and metabolomics trends at least for chlorogenic acid. Importantly, similar trends in gut microbiota were observed in most human subjects. It appeared that low initial abundance of Ruminococcus is limiting the "prebiotic" impact of tart cherries, potentially making it a keystone species.

Significance: To conclude, our results indicate a potential "prebiotic" effect of tart cherries polyphenols on the human healthy gut microbiota. Additional studies are under way to determine the metabolomics trends in the human samples, as well as metagenomic studies. Future studies are envisioned that would include strategies to stimulate Ruminococcus, thereby maximizing the prebiotic effect.