Effects of Sweet Potato Starch and Soybean Protein Isolate on Konjac Gel Properties and Preparation of Composite Gels

The effects of adding different amounts of sweet potato starch (SPS) and soy protein isolate (SPI) on the texture, color, sensory evaluation, moisture distribution, rheological properties and microstructure of konjac gels were investigated. The results showed that the increase in SPS concentration from 0% to 2.5% had a significant effect (P < 0.05) on the textural properties of konjac gels, increasing the hardness and elasticity by 86.43% and 27.69%, respectively, and significantly increasing the gel strength and water-holding capacity (P < 0.05); the addition of SPI below 2% significantly increased the L* and b* values, gel strength and water-holding capacity of gels (P < 0.05) as well as the hardness and elasticity by 13.41% and 15.38%, respectively, and decreased the adhesiveness by 54.19%. The results of rheological analysis showed that the G’ and G” values of gels gradually increased with increasing concentration of SPS and SPI, indicating the formation of a stronger gel structure. Low-field nuclear magnetic resonance (NMR) results showed that the addition of SPS and SPI significantly increased the content bound water in the gel system (P < 0.05), with no significant changes in free water content or relaxation time. The textural properties of the composite gels were further improved by optimized addition of SPS and SPI. Scanning electron microscopy (SEM) results showed that the optimized composite gels formed a denser structure that was continuous and stable. The optimal concentrations of SPS and SPI in the composite gels were 2.5% and 1.0%, respectively. Overall, the results of this study provide a good experimental and theoretical basis for the application of konjac gels in ready-to-eat foods.