Influence of sucrose and acid on the structure and rheological properties of salt-induced soy protein isolate gel

Abstract

In this study, structural, rheological properties and the fractal dimension of soy protein isolate (SPI) cold-set gels made with different concentrations of sucrose and acid were determined. SPI dispersions were heated above those denaturation temperatures (97 °C) in the presence or absence of sucrose. And then gelation was induced by 20 mM CaCl2 and 21.55 mM HCl. Zeta-potential, sulfhydryl group content, rheology, water holding capacity (WHC), microstructure and fractal dimension of soy protein gels were measured. Zeta potential showed that sucrose blocks the revealed net charge of protein. And the sample added acid formed aggregation and its vale close to zero. Rheological measurement revealed that all SPI-sucrose gels were softer than gels without sucrose. As increasing of sucrose contents, storage modulus decreased. And acid treated gels represented larger storage modulus than without acid sample. Gels of SPI with 30% sucrose had largest water holing capacity. And gels of SPI with acid had smallest water holing capacity because they made more compact structure than sample without acid. The image of TEM showed that denser flocs were formed as well as increased aggregation of protein molecules as the concentration of sucrose decreased. Acid and salt combined-treated gels without sucrose showed the most compact microstructure. D f values determined from rheological data using scaling models of Wu and Morbidelli, were the highest (2.80) for combined-treated gel in absence of sucrose among all SPI gels. These results showed that sucrose has protective effect on the protein denaturation. And combination of acid treatment with salt has synergetic effect on improving the properties of cold-set soy protein gel. Rheological properties indicated that acid and salt treatment also has beneficial effect on the rheology of gels. Therefore these results together represented that combination of acid and salt to forming gel may be an important approach to produce cold-set gels with improved rheological and textural properties.