Okara, a by-product of tofu or soymilk, is rich in dietary fibers (DFs) that are mostly insoluble. A wet-type grinder (WG) system was used to produce nanocellulose (NC). We hypothesized that the WG system would increase the dispersion performance and viscosity of okara. These properties of WG-treated okara improve the gel-forming ability of soybean proteins. Here, the suspensions of 2 wt% okara were treated with WG for different passages (1, 3, and 5 times). The particle size distribution (PSD) and viscosity of WG-treated okara decreased and increased, respectively, with different passages. The five-time WG-treated okara homogeneously dispersed in water after 24 h, whereas untreated okara did not. The breaking stress, strain, and water holding capacity of soybean protein isolate (SPI) gels increased upon the addition of WG-treated okara. This effect increased as the number of WG treatments increased. The breaking stress and strain of SPI gels to which different concentrations of the five-time WG-treated okara were added also increased with increasing concentrations of WG-treated okara. These results suggest that NC technology can improve the physicochemical properties of okara and are useful in the development of protein gel-based foods.
The application of okara treated by a wet-type grinder (WG) is discussed in this paper. We examined the effect of WG-treated okara on the mechanical properties and intermolecular forces in soybean protein isolate (SPI) gels. SPI gels were prepared with varying amounts of WG-treated okara, and compression tests were performed. Protein solubility was also examined by homogenizing the gel in four different solutions (S1, 0.6 M sodium chloride (NaCl); S2, 0.6 M NaCl and 1.5 M urea; S3, 0.6 M NaCl and 8.0 M urea; and S4, 1.0 M sodium hydroxide). The gel with WG-treated okara had higher breaking stress but not breaking strain. In contrast, the protein solubility in S3 was lower than those of the gel without okara or with WG-untreated okara. A negative correlation (R2 = 0.86) was observed between breaking stress and protein solubility in S3. These results suggest that WG-treated okara enhanced the hydrophobic interactions of SPI gels because protein solubilization by S3 is caused by the differences in hydrophobic interactions.
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