Olayide S. Lawal

Foaming, gelation and electrophoretic characteristics of mucuna bean (Mucuna pruriens) protein concentrates

Abstract The influences of pH, ionic strength and carbohydrates on the foaming and gelation properties of mucuna bean protein concentrate (MPC) were investigated. The protein concentrate was extracted by alkaline solubilization at pH8, followed by isoelectric precipitation at pH 4. The protein solubility–pH profile showed minimum solubility (19.4%) at pH 4.0 (iso electric point) and maximum solubility (96%) was obtained at pH 12. Foaming capacity increased as the sample concentration increased. Increase in sample concentration also enhanced foaming stability at the various times studied. pH had a pronounced effect on the foaming properties of MPC. At pH 4, MPC exhibited minimum foaming capacity and maximum foaming stability. At lower pH values, there was enhanced foaming capacity and a reduction in the foaming stability. Alkaline media (pH 8 and 10) enhanced foaming but the foams were less stable. Sucrose, maltose, lactose and potato starch improved the foaming capacity and stability of the protein concentrate. Increase in ionic strength, from 0.1 to 0.4 M, improved foaming capacity and stability, while further increase beyond the ionic strength resulted in a reduction of the foaming properties. In all cases studied, gelation improved with increases in concentration of the protein concentrate in the media. Gelation properties were reduced in alkaline and acidic media, except at pH 4, where least gelation concentration endpoint (LGE) was 8. Gelation properties of MPC improved in the presence of carbohydrates in the mixture. Gel-forming properties also increased with increases in ionic strength of the media from 0.1 to 0.4 M, while further increase, from 0.6 to 1.0 M, reduced the gelation properties of MPC. Five polypeptide protein sub-units, at apparent molecular weights of 200, 116, 82, 63, and 59 kDa, were obtained from polyacrylamide gel electrophoresis under non-reducing conditions (without 2-mercaptoethanol). In addition, two other sub-units, at apparent molecular weights of 97 and 40 kDa, were obtained under reducing conditions (with 2-mercaptoethanol).

Isolation, chemical modification and physicochemical characterisation of Bambarra groundnut (Voandzeia subterranean) starch and flour

The proximate and physico chemical characterisation of Bambarra groundnut (Voandzeia subterreanea) flour and starch was studied. Oxidation and acetylation of the native starch reduced the percentage ash, crude protein, crude fibre, and crude fat. The swelling capacity increased with increase in temperature for both starch and flour; the acetylated starch, however, showed the highest swelling power. There is increased swelling and solubility in the alkaline region. Oxidized starch had the highest oil and water absorption capacity (3.04 and 2.40 g/g, respectively). The least gelation concentration for the starches ranged from 6 to 10% (w/v), while the alkaline water retention increased when the starches were blended with wheat flour, with the blends of wheat flour and acetylated starch giving the best result. Brabender viscographic studies showed lowering of pasting temperature after oxidation and acetylation, with oxidised starch showing the lowest pasting temperature. Both oxidation and acetylation lowered the peak viscosity (PV), hot paste viscosity (Hv) and cold paste viscosity (Cv). Chemical modification enhanced the stability of the starches with oxidised starch having the highest stability value, followed by acetylated starch.