Distribution of Molecular Weight of Iron and Zinc Compounds in Digests of Globulins (G1, G2) and Albumin Extracts from White Bean (Phaseolus vulgarisL.)

Abstract

The distribution of the molecular weight of iron and zinc compounds in digests of globulins (G1, G2) and albumin extracts from white bean (Phaseolus vulgarisL.) was determined. Albumin was the protein fraction having the highest amounts of both proteins (760 g/kg) and minerals (92 mg/kg of Fe; 69 mg/kg of Zn) but the lowest amounts of dialysable iron (0.9 mg/kg) and zinc (1.7 mg/kg). Among the protein fractions G2 showed the highest amounts of dialysable iron (3.2 mg/kg) and zinc (5.8 mg/kg). The three protein fractions differed mainly in cysteine content, which was higher in albumin compared to both G1 and G2. After the enzymatic digestion, cysteine was two times higher than the extract in the dialysates of G1 and three times higher than the extract in the dialysates of G2. Dialysates of albumin showed an amount of cysteine two times lower than the extract. Gel-filtration of the digests of G1, G2 and albumin evidenced three protein peaks with molecular weights of 1.5 KDa, 1.3 to 1.1 KDa, and 1 KDa. The amino acids content of these fractions was analysed. Our results suggest that cysteine residues might confere the metal binding properties of the peptides deriving from the invitro digestion of the bean protein fractions; therefore cysteine-containing peptides increase the solubility of Fe2+and Zn2+and will probably improve the absorption of these minerals via active transport systems in the intestine.