Fabrication of stable hydrogel microspheres with hydrophobic shell using water-in-water (W/W) Pickering emulsion template.

Hydrogel microspheres are promising for food applications. The water-in-oil (W/O) emulsion template is commonly used to prepare the hydrogel microspheres. However, this method often involves synthetic surfactants and toxic organic solvents to remove the oil phase. The swelling problem of the resultant microspheres is another obstacle. In this study the water-in-water (W/W) emulsion template of gelatin-in-dextran was used to prepare the hydrogel microspheres, without the addition of surfactants, toxic reagents and high energy input. To prevent swelling, zein particles modified with alginate were served as a hydrophobic shell of the gelatin core. The formation evolution of these core-shell microspheres and its relevant factors including phase behavior of the immiscible gelatin/dextran, the binding of zein/alginate and the addition of the modified zein particles were investigated. It was found that small amount of alginate could induce zein particles to adsorb on the gelatin surface, whereas the excess led to adsorption competition. When using 0.6 wt% particles with zein/alginate ratio of 1:0.5, the ideal core-shell microspheres which were fully covered by the particles and with a self-supporting architecture in uniform size (18.8 ± 0.1 μm) and spherical shape were obtained. These microspheres showed remarkable stability under the conditions of heat treatment, varied pHs and salt concentrations and long-term storage either in refrigerator or room environment. Their sizes were easily manipulated by adjusting the concentration and molar mass of the biopolymers. It is believed that the desired stability and tunable sizes of these edible core-shell microspheres could contribute the development of their applications in foods.