Absorption and Metabolism of Mango (Mangifera indica L.) Gallic Acid and Galloyl Glycosides

Abstract

The composition, absorption, metabolism, and excretion of gallic acid, monogalloyl glucose, and gallotannins in mango (Mangifera indica L.) pulp were investigated. Each galloyl derivative was hypothesized to have a different rate of absorption, and their concentrations were compared in the pulp of five mango varieties. The cultivar Ataulfo was found to have the highest concentration of monogalloyl glucose and gallotannins while the cultivar Kent had the lowest. Enzymatic hydrolysis of gallotannins with tannase led to the characterization of six digalloyl glucoses and five trigalloyl glucoses that have the potential to be formed in the colon following gallotannin consumption.

The bioaccessibility of galloyl derivatives was evaluated in both homogenized mango pulp and 0.65 mm^3 cubes following in vitro digestion conditions. Monogalloyl glucose was found to be bioaccessible in both homogenized and cubed mango pulp. However, cubed mango pulp had a significantly higher amount of gallotannins still bound to the fruit following digestion. Gallic acid bioaccessibility significantly increased following digestion in both homogenized and cubed mango pulp, likely from hydrolysis of gallotannins. Additionally, for the first time, the absorption of monogalloyl glucose and gallic acid was investigated in both Caco-2 monolayer transport models and a porcine pharmacokinetic model with no significant differences found in their absorption or ability to produce phase II metabolites.

A method to extract free gallic acid and its metabolites using sodium dodecyl sulfate from plasma was developed, and the method extracted significantly (p<0.05) more pyrogallol, gallic acid, and their phase II metabolites compared to conventional methods that rely on solvent extractions or use of solid phase extraction. The method was reproducible and precise across three standard concentrations from 50 to 500 µg/L. The method is hypothesized to be more effective due to the ability of sodium dodecyl sulfate to denature proteins and inhibit polyphenol-protein interactions.

The pharmacokinetics of mango gallic acid and galloyl glycosides were evaluated in subjects who consumed mango daily for 42 days, and a significant (p<0.05) increase was observed in the urinary excretion of 4-O-methylgallic acid-3-O-sulfate, pyrogallol-O-sulfate, methylpyrogallol-O-sulfate, and catechol-O-sulfate. However, this same significant increase in metabolism was not observed in plasma concentrations. It was proposed that repetitive mango consumption created changes in the gut microbiota population increasing concentration of gallic acid and pyrogallol in the colon, but due to how quickly gallic acid is excreted from the body no accumulation in plasma was observed.