Stability and transformations of raspberry (Rubus idaeus L.) ellagitannins in aqueous solutions
2019
Sójka, Michał | Janowski, Michal | Grzelak-Błaszczyk, Katarzyna
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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