Emulsion-filled gels of soy protein isolate for vehiculation of vitamin D3: Effect of protein solubility on their mechanical and rheological characteristics

The aim of this study was to develop heat-induced gels of soy protein isolate (SPI) filled with Brazil nut oil emulsions encapsulating vitamin D3 (VD3). Before gelation, dispersions produced with different SPI concentrations (11–15%, w/w) were subjected to different pretreatments (manual mixing or mechanical stirring at 800 rpm for 10, 20, and 30 min) and had their protein solubility quantified. The application of mechanical stirring increased the solubility of proteins and decreased the average particle size, affecting the microstructure (observed by confocal laser scanning microscopy) and rheological properties (evaluated by uniaxial compression and small strain oscillatory tests) of the heat-set gels. The incorporation of emulsions (produced with Brazilian nut oil) into gels formed emulsion filled gels (EFGs), which presented higher Young's moduli and σH in comparison to non-filled gels (NFGs), indicating that the oil droplets were active within the matrices. The properties of EFGs subjected to small strain oscillatory tests, varied with the pretreatment conditions and SPI concentrations, highlighting the high influence of protein solubility, matrix inhomogeneities, and droplet clustering for determining the properties of such complex systems. Also, the heat-induced emulsion-filled gels of SPI produced were effective in protecting VD3, presenting good retention after 30 days of storage under refrigeration, and represent promising alternative for the production of future food gelled products.