High loading contents, distribution and stability of β-carotene encapsulated in high internal phase emulsions

High internal phase emulsions (HIPEs), stabilized with genipin crosslinked chitosan (CS) microgels, were found to significantly increase the loading contents of β-carotene, up to 2 wt% with only 0.1 wt% microgel as the emulsifiers. With much smaller amount of emulsifiers less than one-tenth, the loading content of β-carotene in the emulsion system was significantly increased by more than 10 times compared with those reported in literature. CS microgels could well absorb on the oil-water interface and thus effectively reduced the water/oil contact, which turned out to effectively stabilize the crowed oil phases (in polygonal shape) against mechanical perturbation. CS with high molecular weight was inclined to facilitate the formation of HIPEs. With increased loading amount of β-carotene from 0 to 2 wt%, the HIPEs changed from light blue to yellow green, and further to deep red. Meanwhile, the gel strength decreased, making it liquid-like more, which could be feasible for their application in food systems. Laser confocal microscopy results showed that more β-carotene appeared on the surface of the oil droplets in HIPE system with the elevation of β-carotene loading contents. In addition, with the elevation of β-carotene loading contents, increased amount of β-carotene distributed in the creaming layer and the proportion of β-carotene in oil layer decreased after centrifugation of the HIPE samples. Furthermore, β-carotene encapsulated in the HIPE systems could resist ultraviolet irradiation, thermal treatment, as well as iron ions and hydrogen peroxide in aqueous phase, which could be related to the protection effect from the interfacial CS microgel membrane as well as the crowed oil droplets environment. The stability of the HIPEs formula was also enhanced with the elevation of β-carotene loading contents.