Determination of monomeric anthocyanins in red wines based on their degradation with hydrogen peroxide in the presence of Cu(II)
The kinetics of monomeric anthocyanins degradation with hydrogen peroxide was investigated. The reaction was catalyzed by trace amounts of Cu(II) ions, and it was followed spectrophotometricaly at 520 nm applying the initial-rate method. The kinetics parameters of the reaction are reported, and a rate equation is suggested. Based on this reaction, a kinetic method for monomeric anthocyanins determination is proposed. The calibration graph is linear in the range 21.92-131.52 μg/mL. The method was successfully applied to determining the content of monomeric anthocyanins in red wines. The obtained results were in good correlation with the standard pH-differential method results. The newly developed method is simple, inexpensive and efficient for the analysis of large number of samples at room temperature in a short time.
Anthocyanins represent a class of pigments in plants. They are responsible for the brilliant color (red, blue, or purple) of flowers, fruits, and vegetables (1). The anthocyanin molecules are composed of an aglycone anthocyanidin and sugar moieties. The common anthocyanidins found in plants are Cyanidin (Cy), Delphinidin (Dp), Petunidin (Pt), Peonidin (Pn), Malvidin (Mv), and Pelargonidin (Pg) (2). One or more sugar molecules can be linked to anthocyanidin through a glycosidic bond. It was reported that there are more than 600 types of anthocyanins in nature. The structure of these anthocyanins differs in the types of anthocyanidins, sugar molecules and numbers, and types of acyl groups.
Several factors influence anthocyanin stability, including pH, light, oxygen, temperature, enzymes, ascorbic acids, sugars, sulfur dioxide or sulfite salts, metal ions, and copigments (3, 4). Reactive oxygen species (ROS) including hydrogen peroxide (H2O2), hydroxyl radical (?OH), and superoxide anion play an important role in the degradation of plant pigments (5, 6). Ferrous ion in the Fento’s reagent is usually used to pro ...