Gut Microbe Fermentation of <i>Moringa oleifera</i> Leaf Extract Increases Measurable Polyphenols and Improves Barrier Function in a Cell Culture Model

Moringa oleifera is associated with several nutritional and therapeutic benefits. However, there is limited research on how much these health benefits are mediated directly by the plant or through fermentation with intestinal microbes. We examined the interaction between M. oleifera aqueous leaf extract and three common gut microbes whose abundance was significantly altered in previous intervention studies. Growth curves of Escherichia coli, Bifidobacterium longum, and Bacteroides thetaiotaomicron were examined in the presence of increasing concentrations of M. oleifera leaf extract in YCFA media with and without carbohydrates and short chain fatty acids (SCFAs). Anthrone and Fast Blue BB assays were conducted on spent media to measure carbohydrate and phenolic content, respectively. Sterile fermentation supernatants were applied to an in vitro gut barrier model consisting of differentiated Caco-2 monolayers on permeable cell culture inserts and the transepithelial resistance (TEER) was measured. Growth curve analysis demonstrated that the three bacterial isolates tested could grow in the presence of M. oleifera. However, B. longum had a greater increase in total growth, consumed more soluble carbohydrates, and produced more soluble polyphenols using M. oleifera leaf extract as a sole carbohydrate source than the other two microbes. Additionally, B. longum fermentation of both glucose and M. oleifera increased TEER in Caco-2 monolayers significantly more than E. coli fermentation of both carbohydrate sources (p = 0.0007). These results suggest a potential mechanism through which consumption of M. oleifera may promote the growth of probiotic organisms within the human gut to improve gut barrier integrity.