Uniaxial and Viscoelastic Properties of SPI and SPI-Polysaccharide Gels
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Date
2022-03-23
Authors
Abdi Kordlar, Haniye
Journal Title
Journal ISSN
Volume Title
Publisher
University of Waterloo
Abstract
Nowadays, consumption of soy-based products is increasing due to their appealing nutritional profile, affordability, health benefits, and potential to serve as a suitable substitute for dairy-based foods. Textural property is one of the most significant aspects to consider when evaluating the quality of soy protein gels. Textural characteristics of soy-based foods might be improved by using a good selection of ingredients, such as a source of soy protein, coagulants, or other additions like polysaccharides, as well as the experimental conditions, such as heating and coagulation temperature and duration. Variation in the temperature and duration of gelation along with the soy protein sources could result in the production of soy gels with a wide hardness range-from very soft to firm and hard gels.
The goal of this study was to assess the textural characteristics of citric acid-induced soy protein gels, with a particular emphasis on the type and concentration of soy protein sources and polysaccharides. This goal will be achieved by the use of uniaxial compression and viscoelastic properties. The uniaxial compression properties, e.g. fracture stress, fracture strain, and Young’s modulus, could give insight about the gel strength, firmness, and hardness of a gel. On the other hand, the viscoelastic properties, e.g. storage and loss modulus, could provide information about the viscoelasticity and stiffness of a gel.
First, the kinetic of soy protein gelation was analyzed quantitatively for three soy protein sources, 11S, Soy Protein Isolate (SPI), and dried soymilk, under varied conditions, such as heating temperature. The results indicate that SPI gels had a moderate rate of gelation (it was somewhere between 11S and dried soymilk gelation rate) and might achieve higher stiffness (higher G') than both dried soymilk and 11S. G' is a storage modulus of a gel at the end of the gelation process at the coagulation temperature.
As a result, SPI might be chosen as a soy protein source to produce gels with improved viscoelastic characteristics and increased stiffness. In addition, higher rate was observed when heating temperature was increased. Therefore, 95 C as a heating temperature was selected for the subsequent experimental works.
Second, by selecting the SPI as a source of soy protein, citric acid-induced SPI gel was generated. Citric acid was selected as it can generate soy protein gels with similar viscoelastic and textural properties of conventional tofu. The effect of different heating durations, citric acid concentrations, coagulation durations, citric acid states (liquid or solid), and citric acid addition methods on the strength of 8% w/v SPI gel were then visually investigated. The visual observations include analyzing the appearance of a gel (how watery or solid-like material is that) and the ability of a gel to be shaped and hold. According to the findings, the gel with the highest gel strength (deduced from pressing the gel at g.cm^(-2) for 10 minutes) was created with 0.3% w/v citric acid, when citric acid powder was added to the pre-heated SPI solution at 95 C for 30 minutes while constantly stirring, followed by coagulating at 80 C for 60 minutes.
Third, based on the Box-Behnken design, the 0.3% w/v citric acid-induced SPI-polysaccharide gels were created with 8% w/v SPI, 0-4% w/v inulin (I), 0-0.2% w/v starch (S), 0-0.1% w/v guar gum (G), and a mixture of those. The Box-Behnken design was used to assess the dependence of uniaxial and viscoelastic properties to the type and concentration of polysaccharides. Furthermore, starch, inulin, and guar gum can contribute to the SPI gel network and create a gel with higher firmness and viscoelasticity. Mechanical and rheological measurements were taken to determine the texture of SPI-polysaccharide gels. The mechanical and rheological properties analysis revealed that SPI gels containing only one type of polysaccharide (SPI-2% I, SPI-0.1% S, and SPI-0.05% G) can produce much tougher gels with higher gel strength, hardness, and stiffness and superior viscoelastic properties than SPI gel alone. Furthermore, inulin and starch may work synergistically, and their combination (SPI-4% I-0.1% S and SPI-2% I-0.2% S) could be employed to create gels with greater mechanical strength than SPI gel. Gels containing guar gum in combination with inulin, starch, or both, on the other hand, had significantly lower stress fracture point, Young’s modulus, storage modulus, and loss modulus than SPI gel. So, inulin, starch, guar gum, or a combination of starch and inulin might be used to produce harder citric acid induced SPI gels with improved mechanical strength and viscoelasticity.
Description
Keywords
SPI gel, Polysaccharide, Viscoelastic property, Uniaxial compression property