Antiradical and chelating ability of (+)-catechin, procyanidin B1, and a procyanidin-rich fraction isolated from brown sorghum bran

Résumé 0

Introduction: Sorghum varieties of brown pericarp are a rich source of natural antioxidants, among which procyanidins stand out. Currently there is little information on the relationship between the degree of polymerization of sorghum procyanidins and their antioxidant activity against certain free radicals, enzymes, and metals involved in the oxidation processes. For this reason, the present work intends to broaden the knowledge of the antioxidant profile of sorghum procyanidins, considering their degree of polymerization, through the determination of the antiradical (DPPH, ABTS, lipid peroxidation) and chelating ability (copper, zinc) of (+)-catechin (C), procyanidin B1 (PB1), and a procyanidin-rich fraction (PRF) isolated from brown sorghum bran. Method: The monomer of (+)-catechin (C) and the dimer of procyanidin B1 (PB1) were acquired from chemical suppliers, while the sorghum procyanidin-rich fraction (PRF) was isolated through a Sephadex LH-20 column, employing solvent mixtures of methanol/water and aqueous acetone. The PRF was analyzed in an ultra-high performance liquid chromatography system (UHPLC), equipped with a UV-Vis diode array detector (DAD), as well as electrospray ionization (ESI) and quadruple time of flight (QTOF) mass spectrometry (MS) detectors. Subsequently, the following analysis were determined for the monomer C, dimer PB1 and PRF: Second-order rate constants (Ks), considering the initial stage and the overall reaction with DPPH, using a stopped-flow system; the easiness to reduce the peroxidase-generated free radicals (ABTS); inhibition of lipid peroxidation in a linoleic acid emulsion, as well as the ability to chelate Cu(II) and Zn(II). Results: The dimer PB1 and PRF (mixture of oligomers from trimer to decamer), showed higher Ks to directly inhibit DPPH than the monomer C, and also were more effective to decrease the rates of formation of ABTS in the presence of peroxidase. However, the degree of polymerization was not a determining factor in the behavior of procyanidins to inhibit the free radicals formed during the peroxidation of linoleic acid in an emulsion system. Sorghum procyanidins showed greater ability to chelate copper than zinc, and their chelating ability was greater as the degree of polymerization increased. Conclusions: The kinetic behavior of sorghum procyanidins revealed that PRF possess great potential to inhibit different free radicals, as well as for chelating copper.