High pressure-assisted encapsulation of vitamin D2 in reassembled casein micelles

For the encapsulation of vitamin D₂, native casein micelles and vitamin D₂ with or without additional Ca²⁺–P_i were treated at 600 MPa and 37 °C for 60 min. The pressure release rate was set at 20 or 600 MPa/min. Vitamin D₂ was quantified by reversed-phase high-performance liquid chromatography, and physical properties of the micelles were analysed by photon correlation spectroscopy. The results demonstrate that simultaneous application of Ca²⁺–P_i and high pressure treatment with a fast release rate significantly increased loading of vitamin D₂ per casein by 6.9-fold. The addition of Ca²⁺–P_i enhanced micelle aggregation and the vitamin was entrapped within the formed aggregates. However, high pressure treatment without Ca²⁺–P_i with a slow pressure release rate revealed similar results, increasing vitamin D₂ per casein by 6.7-fold. The vitamin D₂ loading in reassembled casein micelles is supposed to be due to hydrophobic interactions between the hydrophobic domains of the micelles.