Impact of the oil droplet size on the oxidative stability of microencapsulated oil

Microencapsulation aims to protect polyunsaturated fatty acids against oxidation by embedding oil droplets in a solid matrix. The effect of the oil droplet size on the oxidation was evaluated under consideration of the non-encapsulated oil and the powder particle size. An O/W emulsion (1.6%(w/w) soy protein; 30.4%(w/w) maltodextrin DE21; 8%(w/w) fish oil) was homogenised at different pressure levels (4, 8, 17.5 and 30 MPa). Emulsions were spray dried and the size of the obtained powders was standardised. Powders were stored for 147 days at 25 degrees C and the hydroperoxide concentration and Anisidine Value in the total- and encapsulated oil measured. The volume mean diameter of oil droplets varied between 0.48 +/- 0.01 and 1.54 +/- 0.07 mu m. Powders containing small oil droplets resulted in fewer oxidation products, which was related to a larger specific surface area and therefore a pronounced chemical stabilisation by soy protein isolate rather than oxygen diffusion phenomena or different encapsulation efficiencies.