Pomegranate ellagitannins stimulate growth of gut bacteria in vitro: Implications for prebiotic and metabolic effects

•Pomegranate stimulated the growth of bifidobacteria and lactobacilli.•Pomegranate inhibited Enterobacteriaceae, clostridia, and Bacteroides fragilis group.•Bifidobacterium and Lactobacillus utilized ellagic and glycosyl ellagic acid.•Pomegranate may have prebiotic effect.•Demonstration of prebiotic properties set the stage for clinical/animal studies.

The present study investigated the effect of pomegranate extract (POMx) and pomegranate juice (POM juice) on the growth of major groups of intestinal bacteria: Enterobacteriaceae, Bacteroides fragilis group, clostridia, bifidobacteria, and lactobacilli, and the utilization of pomegranate polyphenols by Bifidobacterium and Lactobacillus. The total phenolic content of the pomegranate extract and juice was determined using the Folin-Ciocalteau colorimetric method and reported as gallic acid equivalent (GAE). The polyphenol composition was determined by HPLC. Stool specimens were incubated with 400, 100, and 25 μg/ml GAE POMx and POM juice and subjected to selective culture. Bifidobacterium and Lactobacillus strains were incubated with 400 μg/ml GAE POMx and POM juice and metabolites were analyzed. POMx and POM juice increased the mean counts of Bifidobacterium and Lactobacillus and significantly inhibited the growth of B. fragilis group, clostridia, and Enterobacteriaceae in a dose–response manner. Bifidobacterium and Lactobacillus utilized ellagic acid and glycosyl ellagic acid but little or no punicalin was utilized. Neither POMx nor POM juice was converted to urolithins by the test bacteria or the in vitro stool cultures. The effect of pomegranate on the gut bacteria considered to be beneficial (Bifidobacterium and Lactobacillus) suggests that pomegranate may potentially work as a prebiotic. The concept that polyphenols such as those in pomegranate impact gut microbiota populations may establish a new role for polyphenols in human health.