Nutrition, gelation rheology and gel microstructure of isoelectric and ultrafiltered/diafiltered African yam bean (Sphenostylis stenocarpa) protein isolates

Nutrition, gelation rheology and gel properties of ultrafiltered/diafiltered (UD) and isoelectrically precipitated (ISO) African yam bean (AYB) whole protein isolates (WPI) and albumin-rich fractions (AF) were studied. AYB protein recovery with ultrafiltration/diafiltration process was about 20% higher than that of isoelectric precipitation. AYB protein preparations had total phenolics, tannin, flavonoids and phytic acid in the ranges 0.056-0.263 gGAE/100 g, 0.016-0.151 gGAE/100 g, 0.050-0.174 gCE/100 g and 0.249-0.743 g/100 g respectively. Both WPI and AF proteins had one major denaturation endothermic peak. Denaturation temperature of UD proteins were significantly higher than those of corresponding ISO protein i.e. AFUD > AFISO and WPIUD > WPIISO. The enthalpy changes (ΔH) of the major endothermic peak were 6.75, 7.08, 7.89 and 8.43 J/mol for AFISO, WPIUD, WPIISO and AFUD respectively. The gelation temperatures (Tgel) of AFISO and WPIISO were 90.8 and 85.1 °C respectively, while AFUD and WPIUD gelled at higher temperature (Tgel = 95 °C). The G′ values for AFISO, AFUD, WPIISO and WPIUD gels were 26, 176.5, 1.3 and 32.4 kPa respectively. The heat-set gel of AFUD with highest G′ values, had more visible cross-linked network structure and significantly (p < 0.05) higher mechanical textural properties (hardness, elasticity and resilience) than other AYB protein preparations.