Aggregation profile, preparation and nutritional characterization of African yam bean ( Sphenostylis stenocarpa) acid and salt protein isolates

Abstract

Aggregation tendencies of African yam bean ( Sphenostylis stenocarpa) protein in the various aqueous extraction media with Ca 2+, Mg 2+ or at pI (isoelectric point) were determined. Water extractable S. stenocarpa protein aggregates more with addition of either Ca 2+ or Mg 2+ than at pI. In alkaline extractants considered ( except at pH 10), aggregation tendency of the protein is in the order: pI > Ca 2+ > Mg 2+. The protein aggregation trend in salt media is a function of the salt type, aggregation in NaCl solution is of order: Ca 2+ = pI > Mg 2+, while in Na 2SO 4, we had pI > Mg 2+ > Ca 2+. S. stenocarpa protein aggregation was significantly ( P < 0.05) more in Na 2SO 4 than NaCl. The amount of Ca 2+ required for maximum precipitation of S. stenocarpa from alkaline (water-pH10) extractant was higher than that of Na 2SO 4 and more Ca-proteinate was obtained from the alkaline aliquot. The crude protein of the Ca-proteinates and isoelectric protein isolates obtained from salt and alkaline extract were in the range 71.7–91.8% (dry basis). Protein isolate from alkaline extract had significantly ( P < 0.05) higher fat content than the one from salt extract. Isoelectrically precipitated isolates had lower ash content than Ca-proteinates. The percentage ratio of essential to non-essential amino acid was in the range 45–47%. With reference to FAO/WHO standard, the chemical score showed that most of the essential amino acid were in excess, thus, the amino acid distribution of S. stenocarpa protein isolates showed that it can fulfill the essential amino acid requirement of human especially the acid proteins and can be a good protein supplement in food and a wide range of new food products.