Abstract: Crude protein extract from black soybean seeds was fractionated by addition of different concentrations (0, 5, 10, 15, 20 and 25 mmol/L) of divalent cations (Ca2+, Mg2+ and Zn2+). After the precipitated protein fractions (7S globulin and 11S globulin) were freeze dried, total nitrogen was determined by the Kjeldahl method and the yield and purity of the two fractions were measured. The results revealed that the type and concentration of divalent cations significantly affected the yield and purity of 7S and 11S globulin. Based on comprehensive consideration of yield and purity, 10 mmol/L of Mg2+ was selected to extract black soybean globulin. The purity and yield of the obtained 7S protein were (86.29 ± 3.25)% and (2.90 ± 0.14)%, respectively, while the purity and yield of the obtained 11S protein were (87.42 ± 3.30)% and (9.11 ± 0.28)%, respectively. Anthocyanins from black soybean seeds were extracted with ethanol. It turned out that the content of anthocyanins was (0.58 ± 0.03) mg/g and total phenol was (2.22 ± 0.12) mg/g. By high performance liquid chromatography tandem-mass spectrometry (HPLC-MS/MS) analysis, the isolated anthocyanins were characterized as delphinidin-3-O-glucoside, cyanidin 3-O-glucoside, petunidin 3-O-glucoside and mallow-3-O-glucoside, respectively.

Key words: black soybean, fractional extraction, 7S globulin, 11S globulin, anthocyanin