Mechanism of the spontaneous formation of plant protein microcapsules in aqueous solution

Aqueous pea protein isolate (PPI) solutions were investigated as a function of the pH (6-8) and the protein concentration (C = 1-4 wt%). Phase separation was observed below a critical pH and C-pH phase diagrams were determined at different temperatures between 5 and 40 degrees C. The morphology of the solutions after setting the pH was investigated with confocal laser scanning microscopy. It is shown that heating microphase separated systems induces both dispersion of the dense protein phase and formation of permanent crosslinks between the proteins. The relative kinetics of these two processes determines the morphology of the system after heating. Different morphologies, amongst which microcapsules, were obtained depending sensitively on the pH, protein concentration and heating protocol. A mechanism for the microcapsule formation is proposed in terms of nucleation and growth of the low density phase within the dense microdomains, with full redispersion inhibited by the formation of permanent crosslinks.