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).