Gelation Behavior and Rheological Properties of Salt‐ or Acid‐Induced Soy Proteins Soft Tofu‐Type Gels

Abstract

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 Applications The coagulation effect of calcium sulfate and glucono‐δ‐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.

Soft Tofu-Type Gels: Relationship between Volatile Compounds and Sensory Characteristics as Affected by Coagulants and Raw Materials

“…The current study shows a significant (p < 0.05) difference in the textural characteristics of tofu produced with different coagulants. Hardness was higher for acidinduced gels than salt-induced gels, with values varying between 173 and 302 g. A similar tendency for hardness was observed by Murekatete et al [3] but was not in agreement with findings of Hou et al [31], who observed that salt-induced gels were the hardest. The higher the force required in breaking the tofu, the less brittle the tofu is [32].…”

“…Gels made from soybean had L* values of 79.743 and 80.847 while the ones made from SPI had L* values of 75.093 and 76.147. This could be explained by the fact that first, soymilk has a more whitish color than SPI solution due its higher lipids content and second gels made from soybean have a more uniform and denser network with smaller network pore size than the ones made from SPI [3], resulting in higher luminosity, thus higher ability to emit or reflect light. In addition, knowing that in terms of lightness L* ¼ 100 represent the white color while L* ¼ 0 represent the black one, we could conclude that gels made from soybean were lighter than the ones made from SPI.…”

“…The hardness probably is due to denseness and compact structure of the tofu, an implication that GDL has the ability to create a more dense structure by making protein molecules closer due to loss of water during coagulation step [3]. Low holding water capacity has been associated with higher hardness in tofu [32].…”

“…Second, SPI contains less soybean oligosaccharides, isoflavones and trypsin inhibitors, which are flatulence factor, phytoestrogen and allergens, respectively, to some people. Third, SPI tofu process is simpler, cleaner and more controllable [3]. In addition, Poysa and Woodrow [4] reported that different coagulants produce tofu with different textural and flavor properties.…”

“…Slower aggregating rates leaded to the formation of a more homogeneous structure of soy protein and more water trapped in tofu. It was also found that quicker gel formation leaded to a coarse net structure and high water syneresis rate [3].…”