Oxidation of Procyanidins with Various Degrees of Condensation: Influence on the Color-Deepening Phenomenon

Abstract

Color deepening in red rice is a known phenomenon that occurs during postharvest storage. As procyanidins potentially causes this color deepening, we previously subjected synthetic procyanidin B3, a model procyanidin, to chemical oxidation and determined the structures of the products. To further elucidate the effects of various degrees of polymerization on color deepening, in this study we oxidized synthetic procyanidin C2. The intensity of the UV−vis absorption between 300 and 500 nm in the spectrum of the reaction mixture increased with increasing oxidation time. This absorption following the oxidation of procyanidin C2 was more intense than that of procyanidin B3. HPLC-ESI-MS of the oxidized reaction mixture revealed several new peaks that suggested the formation of products with new intramolecular rather than intermolecular bonds. The major product was structurally identified by comparison with the UPLC-ESI-MS/MS data for a synthetic procyanidin C2 oxide, independently prepared by condensing procyanidin B3 oxide and taxifolin.

Role of Grape-Extractable Polyphenols in the Generation of Strecker Aldehydes and in the Instability of Polyfunctional Mercaptans during Model Wine Oxidation

“…Anthocyanins are more reactive toward superoxide radical than catechin, 32 and it is known that polymeric tannins are more antioxidant than monomeric forms. 33 …”

Bioactive procyanidins from dietary sources: The relationship between bioactivity and polymerization degree

“…Most research is centered on procyanidins and involves procyanidin-rich fruits such as blueberries, strawberries, apples, grapes, kiwis, cranberries, cherries, apricots, and mangoes (Feliciano et al, 2012;Hollands et al, 2018;Luo et al, 2018;Ma et al, 2018;Mannozzi et al, 2018;Nemes et al, 2018;Ramirez et al, 2014;Ruiz et al, 2005;Zhu et al, 2019). Some major cultivated crops such as barley, sorghum, red rice, soybeans, and cocoa are also rich in procyanidins (Esatbeyoglu et al, 2015;Gangopadhyay et al, 2016;Hibi & Yanase, 2019;Wang et al, 2018;Zhao et al, 2018). Nuts such as almonds, hazelnuts, walnuts, pistachios, and peanuts are also important sources of procyanidins (Bansode et al, 2014;Grace et al, 2014;Ojeda-Amador et al, 2019;Schmitzer et al, 2011;Tsujita et al, 2013).…”

Characterization of Natural and Alkaline-Oxidized Proanthocyanidins in Plant Extracts by Ultrahigh-Resolution UHPLC-MS/MS

“…A simple and rapid way to improve the usability of plant PAs is to oxidize them to create new PAs with altered molecular structures. Even though the reaction conditions of oxidation are well-known and different reaction mechanisms have been suggested, the corresponding structural changes are mainly known for individual small PAs [14][15][16][17][18]. For example, the oxidation and rearrangement reactions of different monomeric and dimeric flavan-3-ols have been elegantly discussed already 30 years ago, showing that the chemistry of these PAs at alkaline pH is regulated by the formation of A-and/or B-ring quinone-methides as highly reactive intermediates causing the rearrangement reactions and the oxidative conversion of B-type to A-type PAs [15].…”

“…The detailed characterization and understanding of natural and oxidized PAs is challenging, but recent advances in ultra-high-performance liquid chromatographic tandem mass spectrometric (UHPLC-MS/MS) instrumentation with high-resolution mass analyzers have enabled the characterization of many different plant PAs [18,[26][27][28]. The popular mass analyzers for the characterization of PAs have been orbitrap [27,28] and quadrupole time-of-flight (QTOF) [29,30] because of their high-resolution properties, which allow the determination of the exact masses and corresponding molecular formulae of studied PAs in plant extracts.…”