Preparation, characterization, and foaming properties of soy protein nanoparticles by the cross-linking reaction induced by microbial transglutaminase

Native soy proteins have limited surface properties, but fortunately, it is expected that their foaming behaviors can be improved through the enzymatic cross-linking method. In this paper, by using the cross-linking method with microbial transglutaminase (mTG) as the catalyst, soy protein isolate (SPI), soy 8-conglycinin (7S), and soy glycinin (11S) nanoparticles (NPs) were prepared in the molten state of the protein induced by dithiothreitol (DTT). We compared the structural characteristics of these nanoparticles, including particle sizes, morphologies, zeta potentials, surface hydrophobicities, changes of spatial structure, and cross-linking degrees. In addition, their foaming properties, including foamabilities, foam stabilities, and bubble diameters, were also tested. The results show that there are no significant differences in the foamabilities between the native soy proteins and their nanoparticles with similar initial foam heights. However, it is found that 11S NPs have enhanced foam stabilities with longer half-lives and smaller changes in bubble size, which is closely related to their high wettability and cross-linking degree. This study may provide references for the application of soy protein nanoparticles as new foam stabilizers to replace the traditional foaming agents in the food industry.