Effects of whey protein isolate on yuba: microstructure, rheological and mechanical properties

Purpose As a traditional Asian soy product, yuba is a kind of protein–lipid film peeled from the soymilk surface through high-temperature incubation. However, yuba has poor mechanical properties. Therefore, this study aims to improve the mechanical properties and yield of yuba by supplementing whey protein isolate (WPI) into soymilk. Design/methodology/approach WPI was used to blend with soymilk at the level of 0, 4, 8, 12 and 16 g per 100 g soybeans (w/w) to prepare composite yuba. The soymilk with 0–16% WPI was characterized using fluorescence spectroscopy, surface hydrophobicity, zeta-potential measurements, particle size analysis. Moreover, the mechanical properties, yield and microstructure of composite soymilk-derived yuba were also studied. Findings The fluorescence spectroscopy revealed the formation of interactions between WPI and soymilk proteins during thermal treatment. With the increased WPI addition, the surface hydrophobicity value of composite soymilk increased from 562.82 ± 12.5 to 885.11 ± 3.15. The zeta-potential value of composite soymilk with 0–16% WPI increased from −27.89 ± 0.04 mV to −29.33 ± 0.08 mV. Additionally, the protein particles in soymilk aggregated to larger particle sizes due to the enhanced protein-protein interactions. The yuba with 12% WPI reached the maximum tensile strength and yield. The scanning electron microscopy results revealed that composite yuba with the higher level of WPI had a denser surface. The denser structure of composite yuba with WPI was formed through disulfide bonds. Originality/value This work firstly demonstrated that WPI could improve the quality of traditional yuba, which provided new insights for the application of WPI in protein-derived products.