Heat stability and rheological properties of concentrated soy protein/egg white protein composite microparticle dispersions

Random aggregation character and beany flavor limit the application of soy protein products in drinkable and semi-solid protein-rich products that taste smooth and soft. A co-protein strategy was employed to prepare soy protein-based microparticles with improved heat stability and weak gelation ability in this work. Egg white protein (EWP), which served as a free sulfhydryl (SH) donor, was mixed with soy protein isolate (SPI). Microparticulation and spray drying were successively conducted on the mixture, and roughly spherical composite microparticles were obtained. The addition of EWP significantly increased the number of intermolecular disulfide linkage inside the microparticles, which was verified by the determinations of their free SH and cystine levels as well as their extractability in sodium dodecyl sulfate-containing buffers. When re-dispersed in deionized water at a neutral pH condition, most of the composite particles had a diameter ranged from 2 to 20 μm. Their size distribution analysis suggested that there was no significant particle aggregation occurred after this dispersion was heated at 95 °C for 30 min. The frequency-dependent storage moduli indicated that this heated dispersion with a protein concentration of 12 wt% was still a viscous liquid. The tribological test suggested that this dispersion also provided better lubrication for the contact between the soft rubber surfaces. The gas chromatography-mass spectrometry analysis showed that the flavor volatiles content in the composite microparticles was much lower than that in SPI. This might provide another perspective for preparing novel soy protein-based ingredients with improved functionalities for protein-rich foods.