GELATION BEHAVIOR AND RHEOLOGICAL PROPERTIES OF SALT- OR ACID-INDUCED SOY PROTEINS SOFT TOFU-TYPE GELS

Oscillatory tests data were analyzed using the power law and the weak gel models. Acid-induced gels had higher storage modulus (G) than salt-induced gels. During gelation, both moduli increased gradually but never reached a steady state, with G being higher than G. Under applied parameters, salt-induced gels made from soybean coagulated faster than the ones made from soy protein isolate (SPI). Syneresis rate in salt-induced gels was significantly lower than in acid-induced gels, with SPI acid-induced gel having the highest rate (36.72%) and soybean salt-induced gel having the lowest (14.77%). Furthermore, salt-induced gels resulted in a reduction in shear deformation at fracture and an increase in the shear stress at yielding, whereas the shear stress at yielding was reduced and the shear deformation at fracture was increased in both acid-induced gels. It was observed that gels made from soybean had a more uniform and denser network with smaller network pore size than the ones made from SPI. Practical ApplicationsThe coagulation effect of calcium sulfate and glucono--lactone was established in this comparative study, and also the use of soybean and soy protein isolate in salt- or acid-induced soft tofu-type gels have shown the effects of other soybean constituents besides proteins on the rheological properties and gelling process. Therefore, a better understanding of the gelation mechanism, small- and large-scale deformations of soy protein curd, is industrially relevant, as it will allow for better process design, monitoring and quality control, thus potentially lead to the development of novel soy-based products. In addition, the parameters and conditions used were close to the ones used during soft silken tofu making, therefore making the process application easier.