Physicochemical and functional properties of kidney bean albumin and globulin protein fractions

Albumin and globulin proteins obtained after ammonium sulfate precipitation of proteins from red kidney beans were investigated for their functional properties. Protein contents of the fractions were found to be 40 and 91.5% for albumin and globulin, respectively. Amino acid analysis showed that sulfur-containing amino acids (cysteine and methionine) were limiting but the proteins were rich in acidic amino acids. SDS-PAGE pattern of the globulin fraction revealed two major polypeptides (7S vicilin) with molecular weights (MW) of ~ 43 and 45 kDa in addition to three minor low MW (< 25 kDa) polypeptides. In contrast the albumin had one major polypeptide with estimated MW of 27 kDa. The solubility profiles showed minimum values at pH 4-6 for globulin but the albumin was more than 60% soluble at pH 3-9. Water holding and oil binding capacity were, respectively, 3.4 and 2.37 mL/g for globulin, which were significantly higher (p < 0.05) than the values of 2.56 and 1.87 mL/g for albumin. The least gelation concentration was 6% for globulin compared with a significantly higher (p < 0.05) 16% for albumin.

► Kidney bean globulin fraction was made up predominantly of 7S vicilin polypeptides. ► Kidney bean albumin fraction is a glycoprotein with about 45% (w/w) carbohydrate content. ► The albumins had greater solubility at pH 3-6 than the globulin. ► The globulins formed solid gels at lower protein concentrations than the albumins. ► The globulins had higher oil and water holding capacities than the albumins.