Inspired by denatured globular protein conformational structures, soy protein isolate (SPI) aqueous solutions under neutral pH without the addition of any chemicals were studied under different mechanical treatments. Compared with the traditional magnetic stirring treatment (MS), high-intensity ultrasonication (US), high-speed mechanical shearing (SH), and their combined treatments (USSH, SHUS) were able to better dissolve SPI and further swell and deform the globular conformation. Higher solubility, lower turbidity, enlarged particle size, much uniform particle size distribution, higher free sulfhydryl groups content, increased fluorescence intensity, higher surface hydrophobicity, and higher viscosity SPI solution properties were detected from all these US and SH treated protein samples. Among them, the USSH treated SPI solution was characterized to have the proteins in the best modified conformational structure. The polymer chain relaxation and degradation were also observed from the denatured protein solutions after up to 12 days of treatments. A schematic structure model focusing on the effect of dissolution and denaturation of SPI was established to better explain the results.

Conformations of soy proteins in soy protein isolate (SPI) aqueous dispersions determine the processability of the SPI and are affected significantly by pH conditions and the addition of a plasticizer, when mechanical forces are present. In this work, the effect of chemical forces facilitating the physical treatment in modifying the conformational structures of soy proteins was investigated. SPI in a H2O system under extreme pH conditions and a glycerol/H2O system was subjected to a combination of ultrasound and shear (USSH) treatments to increase the processability of soy proteins by conformational denaturation. In the H2O system, the combination of the USSH treatment and different pH conditions provides varied properties of denatured SPI solutions and fabricated SPI–cellophane composite films. In the glycerol/H2O system, with an increased and stabilized viscosity, a higher content of sulfhydryl groups, swelled particle sizes, and unfolded protein structures, glycerol proved to be an efficient structural stabilizing agent assisting the deformation of soy proteins under the USSH treatment. The combinations of the USSH treatment and extreme pH conditions or the glycerol/H2O system proved to be efficient processing methods for increasing the processability of soy proteins as a raw material in products.

Metrics & MoreArticle RecommendationsT he caption of Figure 10 was mistakenly described in the article. The corrected caption to Figure 10 is as follows: "Appearance of SPI−cellophane composite films cast out of a 5 wt % SPI dispersion in 100% H 2 O (a), 10% Gly/H 2 O (b), and 30% Gly/H 2 O (c) on commercial cellophane films. (d) Mechanical strain and stress at break of the prepared composite films. Data are expressed as the mean ± SD of three replicates. Means with different letters on the bars differ significantly at the p ≤ 0.05 level."