Heat-induced gelation properties of isoelectric and ultrafiltered sweet potato protein isolate and their gel microstructure

Heat-induced gelation properties of sweet potato proteins (SPP) and their gel network structure were studied. The protein considered were ultrafiltered/diafiltered sweet potato (UDSP) and isoelectrically precipitated sweet potato (IPSP) proteins. The minimum gelation concentration of IPSP and UDSP proteins in phosphate buffer (pH 7) after heat treatment at 95 degrees C were 2% and 4% respectively. Gelling temperature (T-gel) of 10% UDSP and IPSP protein dispersions were 79.4 degrees C and 76 degrees C respectively. Both UDSP and IPSP gels were slightly frequency dependent with storage modulus (G') and angular frequency (omega) relationship of G'similar to omega(0.11) and G'similar to omega(0.13) for UDSP and IPSP gels respectively. The solubility of these protein gels in different aqueous solvent with/without denaturizing agent revealed that hydrophobic, hydrogen bonding and disulphide (-S-S-) covalent interactions were involved in their gel molecular network However, -S-S- interactions were significantly (p<0.05) higher in both UDSP and IPSP protein gels than the hydrophobic and hydrogen bonding. IPSP gel had significantly higher mechanical properties than UDSP gels. Scanning electron microscopy revealed that IPSP gels had repeating fine-stranded network structure, while UDSP gel had dense, spherical particulate network appearance. (C) 2012 Elsevier Ltd. All rights reserved.