Rheological properties of African yam bean (Sphenostylis stenocarpa Hochst Ex A Rich) calcium proteinate and isoelectric protein isolates

The rheological characterizations of African yam bean (Sphenostylis stenocarpa) protein dispersions were investigated Isoelectrically precipitated protein-IPalk and IPsalt isolates obtained from alkaline and salt extractions respectively were more soluble than calcium precipitated proteins (CaPalk and CaPsalt) at pH 3 7 and 8 Regression analysis showed that Power law Casson and Bingham rheological models adequately described theological behaviors of S stenocarpa protein dispersion However Power law gave the best fit The flow behavior indices (n) at different ionic strength pH and temperature media were less than unity indicating that S stenocarpa protein dispersion exhibited pseudoplastic behaviors under the conditions tested Salt extracted proteins were more pseudoplastic than alkali extracted counterpart with n for salt extracted proteins (IPsalt & CaPsalt) lower than that of alkali extracted protein (CaPalk & CaPsalt) This is a numerical indication that salt extracted S stenocarpa proteins were of larger shear-thinning tendency than the alkali extracted proteins The consistency coefficients k of isoelectrically precipitated protein (0 305-0 327 Pas(n)) were significantly (P < 0 05) higher than that of calcium proteinates in the range ranged 0 167-0 180 Pas(n) Both isoelectrically precipitated proteins and calcium proteinates exhibited yield stress however isoelectrically precipitated S stenocarpa protein exhibited significantly (P < 0 05) higher yield stress (0 275-0 308 Pa) than the calcium proteinates (0 148 -0 165 Pa) The effect of temperature on apparent viscosity of the proteins was evaluated using an Arrhenius-type equation The activation energies (E-a) obtained were in the range 33-51 2 and 42 6 -55 5 Jmol(-1) for calcium proteinate and isoelectrically precipitated protein respectively (C) 2010 Elsevier Ltd All rights reserved