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 f ollowed by acid precipitation at pH 4.5. Physicochemical and functiona l 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 coagulabilit y, aromatic hydrophobicity (ARH) and fluorescence intensity (FI) were high at low pH and gradually decreased with increasing pH. Protein sol ubility and foam stability were low at low pH and high NaCl concentrat ions, but increased with increase in pH. The relationships of ARH, FI and UV-absorption maxima (Amax) with the functional properties were de termined using multiple regression analyses. Significant (P-s less tha n or equal to 0.05) equations describing the functional properties on the basis of ARH, FI and Amax were generated; however, the contributio n of these parameters was low as indicated by the low correlation coef ficient. Regression results suggest that other physicochemical propert ies (e.g. electrostatic interactions) were also important contributors to the functional properties examined.