Effects of casein micellar structure on the stability of milk protein-based conjugated linoleic acid microcapsules

The effects of casein micellar structure on the stability of milk protein-based conjugated linoleic acid (CLA) microcapsules were investigated. CLA emulsions were prepared with milk protein concentrates (MPC) or a mixture of whey protein isolates (WPI) and sodium caseinate (SC). Larger droplet sizes and wider size distributions were observed for MPC-CLA emulsions, where the varied sizes and heterogeneous protein particles with different rigidity discontinuously adsorbed on the oil droplets. Aggregated oil droplets with porous walls were found on the inner surface of MPC-CLA spray-dried powders. These microcapsules also had lower encapsulation efficiency and unfavorable oxidative stability. For MPC-CLA, 17% of the CLA remained after 45 days at 35 °C, while ∼80% was retained for the WPI+SC-CLA microcapsules. The adverse effect of the casein micellar structure suggested that modification of casein micelles will be needed to improve the efficiency and chemical stability of such microcapsules.