Comparison of Anthocyanins, Proanthocyanidin Oligomers and Antioxidant Capacity between Cowpea and Grain Legumes with Colored Seed Coat

Abstract

The aim of this study was to investigate the composition and contents of anthocyanins and proanthocyanidins, and the antioxidant capacity of black and red cowpeas grown in Japan, with comparison to grain legumes (black kidney beans, black soybeans, and azuki beans) commonly consumed in Japan. This study revealed that black cowpeas contained seven anthocyanins, the 3-O-galactosides and 3-O-glucosides of cyanidin and delphinidin, and the 3-O-glucosides of malvidin, peonidin, and petunidin, at higher levels than other grain legumes. In addition, black and red cowpeas were rich in proanthocyanidin oligomers (monomers to hexamers) when compared with other grain legumes. Among these, black and red cowpeas showed potent hydrophilic oxygen radical absorbance capacity (H-ORAC), reaching 540.6 and 367.5 μmol-Trolox equivalents/g-dry matter, respectively. The contributions of anthocyanins and proanthocyanidin oligomers to H-ORAC values were 45.8 % and 17.5 % in black and red cowpeas, respectively.

Proximate, Anthocyanin and Oligomeric Proanthocyanidin Compositions of Cowpeas [Vigna unguiculata (L.) Walp] Cultivated in Southwest Japan

“…In addition, Ojwang et al, (2012) determined the anthocyanin composition of black cowpea, in which delphinidin-3-Oglucoside was the most predominant anthocyanin, followed by cyanidin-3-O-glucoside, petunidin-3-O-glucoside and malvidin-3-O-glucoside. In addition, similar results were obtained in our previous study (Orita et al, 2019) using black cowpeas grown in regions of northern Japan other than the Hokkaido region. In this study, in both black cowpeas 1 and 2 that were grown in the Okinawa region, the most abundant anthocyanin was cyanidin-3-O-glucoside, followed by delphinidin-3-O-glucoside, petunidin-3-O-glucoside, and malvidin-3-O-glucoside, the content was significantly different among them.…”

“…In addition, cowpeas grown in the Okinawa region showed significantly higher H-ORAC, compared to red cowpeas grown in the Hokkaido region. Our previous study (Orita et al, 2019) demonstrated that cowpeas grown in northwest regions other than the Hokkaido region showed the highest H-ORAC values among grain legumes commonly consumed in Japan. These values observed in red and black cowpeas were higher than that of other cowpeas in this study.…”

“…Anthocyanins in grain legume sample were extracted with 1% (v/v) hydrochloric acidmethanol as previously described (Orita et al, 2019).…”

“…Extraction of phenolic compounds: Phenolic compounds in grain legume sample was extracted with an extraction solvent (acetone: water: acetic acid = 70:29.5:0.5, v/v) (Orita et al, 2019).…”

“…Anthocyanins were analyzed by HPLC equipped with a photodiode array detector according to the method described by Orita et al (2019). Identification was performed by comparing retention times and UV-VIS absorption spectra with commercially available anthocyanin standards.…”