Fabrication of soy protein microgels via two top-down methods and characterization of the foaming behavior

The aim of this study was to design and characterize soy protein microgels (SPM) using heat-induced (H-SPM) and enzyme cross-linking (E-SPM) methods, and then compared their conformational differences with soy protein isolate (SPI) and explored their foaming behavior. The results showed that transglutaminase-induced covalent cross-linking could fabricate SPM more effectively than that of simple heat treatment, resulting in larger particle sizes, higher surface charge and lower surface hydrophobicity, as well as more robust internal integrity and more ordered structure. Compared with SPI and H-SPM, the foamability of E-SPM decreased by 18.60% and 25.53%, respectively, while the short-term foam stability (60 min) increased by 20.50% and 5.81%, respectively. In terms of long-term foam stability, the foam volume of SPI and H-SPM eventually disappeared after standing for 300 min, while E-SPM still had a considerable foam volume (11.33 mL). Microstructure evaluation suggested that E-SPM stabilized foams via a Pickering-type mechanism. This study will facilitate the applications of SPM as a plant protein-based Pickering-type foam stabilizer in terms of generating aerated foods with long-term foam stability.