Identification of anthocyanins in black soybean (Glycine max (L.) Merr.) varieties

Anthocyanin pigments in black soybean (Glycine max (L.) Merr.) varieties as Tawonkong (TW) and Geomjeongkong-2 (G2) were identified to evaluate their potentials as nutritional function, natural colorant or functional foods. Anthocyanin extraction was conducted with acidified methanol with 0.1 M HCl (85:15, v/v). Identification of anthocyanin was conducted by comparison with purified standards by HPLC and mass spectrometry (MS). G2 showed six different types of pigments by HPLC, whereas TW showed seven pigments. Three major anthocyanins (peaks 1, 3, 4) were detected in both varieties and peak 1 was characterized as delphinidin-3-O-β-D-glucoside, peak 3 as cyanidin-3-O-β-D-glucoside (C3G), and peak 4 as petunidin-3-O-β-D-glucoside by comparison of chromatographic properties with authentic standards and MS. Minor peaks 5, 6 and 7 in TW were tentatively identified as pelargonidin-3-O-glucoside, pelargonidin-3-O-(6″-malonylglucoside) and cyanidin on the basis of MS. MS with major ions at 287 and 449 of peak 2 were exactly same as those of peak 3 meaning that peak 2 has cyanidin and other hexose different from glucose. After acid hydrolysis of fractioned peak 2, HPLC showed the hexose as galactose, and peak 2 was identified as C3Glactose. The most abundant anthocyanin in black soybean (Glycine max (L.) Merr.) was C3G and G2 showed the higher amount of total anthocyanins than TW (p < 0.001).