Effects of milk protein concentrate decalcification on casein micelles as carriers for lutein

The effects of partial calcium depletion of milk protein concentrates (MPC) on the dissociation of casein micelles were investigated. MPC after decalcification with varying calcium content (0.93, 0.80, 0.69, 0.53, 0.41 and 0.39 mmol/L) were produced by ion-exchange treatment. The compositions and structural properties of the concentrates were analyzed using SDS-PAGE, UV–Vis absorption and fluorescence spectroscopy, circular dichroism spectroscopy, X-ray diffraction, and measurement of surface hydrophobicity. Although the decalcification treatment had no effect on the protein composition of MPC, it was found to influence the micellar micromorphology of the casein micelles, as shown by transmission electron microscopy. Decreases in calcium content from 0.93 to 0.41 mmol/L were associated with reductions in the sizes of the micelles which were spherical in shape. The micelles delete changed shape at 0.39 mmol/L (calcium content). The zeta potential of MPC and decalcified MPC micelles changed as calcium concentration decreased. Decalcified MPC with the lowest calcium content had the highest surface charge, with differences in surface charge likely influencing micelle dissociation. The decalcification of MPC significantly influenced the loading and release of lutein by the micelles. At 0.69 mmol/L calcium content, MPC micelles had well-dispersed spherical shapes with markedly smaller particle size, together with the highest loading capacity and encapsulation efficiency. Simulated digestion showed that the micelles of moderately decalcified milk protein concentrates promoted lutein stability and its release in the intestine. These findings open up the possibility of fabricating MPC with customized functionality, especially in the delivery of fat-soluble pigments in food industry.