The effects of pH and rat intestinal contents on the liberation of ellagic acid from purified and crude ellagitannins.

This study was undertaken to measure the liberation in vitro of ellagic acid [2], a naturally occurring inhibitor of carcinogenesis, from precursor ellagitannins under conditions found in the gut tract. Enzymes, namely beta-glucosidase, esterases, and alpha-amylase, were incubated with raspberry extract. In addition, raspberry extract and casuarictin [1] were treated at different pH's and with the contents of small intestine and cecum from rats fed AIN-76A diet. The esterase activity of the enzyme samples was measured spectrophotometrically using p-nitrophenol acetate as the substrate, and the amount of ellagic acid [2] released from all samples was analyzed by hplc. The hydrolysis of the ellagitannins was not catalyzed by any of the purified enzymes tested, and components of the raspberry extract were found to inhibit the purified esterases noncompetitively. Casuarictin [1] was hydrolyzed to yield high quantities of ellagic acid [2] when placed in buffer at pH 7 and 8, or when incubated with cecal contents for two hours. The release of ellagic acid [2] from the raspberry extract was optimal at pH 8, and maximal release in cecal contents occurred with 1 h. Small intestinal contents had no significant effect on ellagic acid liberation from either casuarictin [1] or raspberry extract.