Functionality of African locust bean (Parkia biglobossa) protein isolate:: effects of pH, ionic strength and various protein concentrations

A protein isolate was prepared from African locust bean (ALBPI) and the functional properties were investigated under the influence of pH, ionic strength and varying protein concentration. Protein solubility diminished as the pH increased from 2 to 4.5, after which further increase in pH increased it progressively. The oil absorption capacity of ALBPI was 1.97 ml/g protein. Water absorption capacity increased when ionic strength of the medium increased to 0.2 M but diminished with further increase in ionic strength. Gelation properties improved at pH 4. The results indicate improvement in gelation capacity as the ionic strength of protein solution increased from 0.1 to 0.2 M while further increase in ionic strength caused the gelation tendency to decline. Increase in concentration favoured emulsifying activity (EA) and stability (ES) up to 4% (w/v) concentration, while further increase from 6% to 10% (w/v) diminished emulsifying properties. Also, initial increase in ionic strength, up to 0.2 M, improved both emulsifying activity and stability while further increase in ionic strength progressively reduced emulsifying properties. Maximum emulsifying activity and stability were at pH 10 while minimum values were obtained at pH 4. Foam capacity and stability increased as the protein concentration increased. Increase in ionic strength from 0 to 0.2 M increased the foam capacity (FC) and stability (FS) but foam capacity was reduced as the ionic strength increased further. Foam capacity and stability were pH-dependent. A minimum value of 32.7% was recorded at pH 4 while further increase in pH increased the foam capacity progressively until it reached a maximum (86.8%) at pH 10. Contrarily, maximum foam stability was recorded at pH 4 while foam stability diminished as the pH of the protein solution increased. (C) 2003 Elsevier Ltd. All rights reserved.