Ellagitannins are known to possess many beneficial and health-promoting properties, including antioxidant and antimicrobial effects, arising from the activity of both native compounds and the products of their degradation or metabolism. The wide range of beneficial properties is attributable to the great structural variety of these compounds, even though all of them belong to the same polyphenolic group, namely hydrolyzable tannins. Therefore, the potential of individual ellagitannins must be studied separately with the view to their application, as natural substances, in medicine or the food industry. The objective of the present work was to elucidate the effects of temperature and medium pH on the stability of the two main raspberry ellagitannins, i.e., lambertianin C and sanguiin H-6, in aqueous solutions. Experiments were conducted within the temperature range of 20-80 °C and pH 2-8 over 0-24 h of incubation. The content of the studied ellagitannins and the products of their decomposition was investigated using HPLC-DAD and LC-MS, respectively, with an Orbitrap detector. It has been found that the studied ellagitannins are stable in acidic conditions, but are rapidly degraded in neutral and mildly basic media at elevated temperature (60-80 °C). In mildly acidic conditions (pH 6) ellagitannins hydrolyze to intermediate products, that is, sanguiin H-10 isomers, sanguiin H-2, and galloyl-HHDP-glucose isomers, with the main end products being ellagic and gallic acids. In addition to hydrolysis, ellagitannins may also undergo oxidation to compounds containing a dehydrohexahydroxydiphenoyl (DHHDP) group, also accompanied by the presence of brevifolin carboxylic acid, a product of DHHDP hydrolysis.

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PurposeWe investigated the effects of dietary supplementation with strawberry extracts rich in ETs and fructo-oligosaccharides (FOS) on the intestinal microbiota and the formation of bacterial metabolites in the distal intestine, as well as the absorption of ET metabolites and antioxidant status in rats.MethodsRats were allocated into six groups of eight animals each and fed for 4 weeks with a control diet (group C), a control diet supplemented with FOS (group C + FOS) or modifications of these diets, in which a monomeric or dimeric ET-rich extract was added (groups ME and ME + FOS or DE and DE + FOS, respectively).ResultsThe extract addition, the FOS addition and their interaction significantly affected the total and selected bacterial counts in the caecal digesta (all P < 0.005). The total bacterial count was the highest in group C + FOS, lower in group DE and the lowest in group ME + FOS (10.6, 10.3 and 8.52 log cells/g, respectively; P ≤ 0.05). The total caecal content of ET metabolites was higher in the ME and ME + FOS group than in the DE and DE + FOS group, respectively (67.8 and 89.5 vs. 13.0 and 18.0 µg/g, respectively; P < 0.001). The total plasma concentration of ET metabolites was higher in the ME + FOS and DE + FOS group than in the ME group (248 and 281 vs. 8.13 ng/mL, respectively; P < 0.001).ConclusionsETs of the monomeric ET-rich extract are more prone to intestinal breakdown than those of the dimeric ET-rich extract, and absorption of their metabolites can be increased by dietary FOS; however, together, they evoke strong antibacterial activity.

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