Some physicochemical and functional properties of cowpea (Vigna unguiculata) isoelectric protein isolate as a function of pH and salt concentration

Cowpea isoelectric protein isolate was prepared by alkali extraction followed by acid precipitation at pH 4.5. Physicochemical and functional properties of the isolate were determined at various combinations of pH (3-8) and NaCl concentrations (0.5-2.0 M). Results showed that at all NaCl concentrations, emulsifying activity index, heat coagulability, aromatic hydrophobicity (ARH) and fluorescence intensity (FI) were high at low pH and gradually decreased with increasing pH. Protein solubility and foam stability were low at low pH and high NaCl concentrations, but increased with increase in pH. The relationships of ARH, FI and UV-absorption maxima (Amax) with the functional properties were determined using multiple regression analyses. Significant (P-s less than or equal to 0.05) equations describing the functional properties on the basis of ARH, FI and Amax were generated; however, the contribution of these parameters was low as indicated by the low correlation coefficient. Regression results suggest that other physicochemical properties (e.g. electrostatic interactions) were also important contributors to the functional properties examined.