Impact of pH on the fabrication of egg white reinforced soy protein composite microgels for gastrointestinal delivery purposes.

Protein molecules such as soy protein isolate (SPI) and egg white (EW) are highly promising materials for developing hydrogels (especially micro/nanogels) for the encapsulation, protection and controlled release of bioactive substances. However, there are limited numbers of studies on the formulation and behavior of these two gelling materials as microgels. In our study, composite microgels of SPI and EW at various component ratios and pH conditions have been successfully prepared; the rheological behavior and structural properties of these composite microgels before, during and after in vitro digestion have been analyzed; and their performance in curcumin encapsulation and gastrointestinal delivery has also been investigated. It was concluded that the SPI-EW composites at a mass ratio of 50 : 50 showed the best gelling properties in terms of storage modulus. Composite microgels prepared at pH 4 had larger particle sizes with more compact structures than those prepared at pH 7, due to their acidic complex coacervation, and therefore were more resistant to gastrointestinal digestion. The results suggest that the SPI-EW composite microgel particles prepared at pH 4 could achieve better sustained-release of curcumin in the in vitro gastrointestinal tract, with preserved antioxidant activity. Our study shows promise for the utilization of protein-based composite micro/nanogels for oral delivery applications.