To improve quality and production efficiency of yuba films, this study aimed to clarify the mechanism underlying the formation of yuba films, by investigating the effects of lipids and elucidating the molecular interaction between proteins and lipids. A thin film with dense structure was produced after heating soybean protein isolate (SPI) solution, whereas a thick film with a porous structure was formed upon heating soybean milk, and SPI solution with added soybean oil, indicating that lipids are indispensable to the formation of yuba films. FT-IR imaging demonstrated the distribution of lipids as oil bodies in the protein phase of the yuba films. Analysis of structural proteins by diagonal two-dimensional electrophoresis (D-2DE) identified a specific 17-kDa protein in the yuba films, which was identified to be oleosin 1-like by LC/MS/MS. This lipophilic protein is known to have a cysteine residue. The existence of oleosin in the yuba films suggested the presence of disulfide (SS) bonds in polymers formed by oleosin with β-conglycinin (β-GCα), β-conglycinin (β-GCα′) and glycinin acidic (GA), and with GA and glycinin basic (GB) protein subunits. These proteins and oil bodies polymerize to form an aggregate and form the structural framework of yuba films.
