Polypeptide composition and functional properties of African yam bean seed (Sphenostylis stenocarpa) albumin, globulin and protein concentrate

Abstract

In this study, the functional properties of African yam bean seed protein concentrate (64.21% protein) as well as albumin (59.51% protein) and globulin (91.68% protein) fractions were investigated. Non-reducing sodium dodecyl sulfate polyacrylamide gel electrophoresis showed that the albumin consisted of mostly polypeptides with sizes ≤26 kDa. The protein concentrate and globulin had similar polypeptide composition while some of the bigger size (46–61 kDa) polypeptides were not present in the albumin. The albumin and globulin fractions had higher fluorescence intensity values than the protein concentrate at all measured pH values. Gelling ability was significantly (p < 0.05) stronger for the albumin (probably due to the high carbohydrate content) with least gelation concentration of 8% when compared to the 10% for protein concentrate and 14% for globulin. In contrast, oil absorption capacity significantly (p < 0.05) decreased in the following order: albumin (8.10 g/g) > globulin (4.75 g/g) > protein concentrate (4.05 g/g). At pH 3.0–9.0, the albumin had significantly (p < 0.05) higher solubility than the protein concentrate and globulin. The albumin also had significantly (p < 0.05) higher foaming capacity but similar emulsion forming ability as the protein concentrate. Emulsion forming ability and stability of globulin formed emulsions were poorer (p < 0.05) than those of albumin and protein concentrate. While non-protein components could have influenced some of the properties, the results suggest that smaller size of the albumin polypeptides could be responsible for some of the observed superior functional properties when compared to the globulin and protein concentrate that contained bigger size polypeptides.