(76c) Particle Design of Spray Dried Fat Powder - Impact of Lipid Distribution within Particles on Oxidative Stability

Encapsulation is an established technique to protect sensitive materials like nutritionally valuable poly unsaturated fatty acids from environmental factors and to enhance oxidative stability. Hereby O/W emulsions are spray dried, so that lipid droplets are embedded in a solid matrix building an oxygen diffusion barrier. However, some oil droplets are in contact with the particle surface and therefore exposed to oxygen. It is assumed that the so-called surface oil and the oxygen diffusion play major roles for the oxidative stability from a physical point of view.

The aim of this study is to investigate the lipid distribution within the powder particle and its impact on the oxidative stability. With respect to particle design it is still unclear what causes surface oil and which process condition are ideal. In this context questions on the impact of oil load, droplet size and oxygen diffusion are answered.

In a first part the design of particles encapsulating lipids regarding oil distribution was studied by a systematic approach, which divided the production process into three focus areas: the emulsion properties, the feed atomization and drying conditions. Hereby the effect of the oil content, droplet size, nozzle type and pressure as well as the drying rate on the oil distribution regarding amount of surface oil and droplet size distribution was evaluated.

In a second part the impact of the surface oil and oxygen diffusion was quantified by using experiments and simulation. Experimentally, the contribution of surface- and encapsulated oil to the overall oxidization was measured separately. Therefore, encapsulated fish oil powders were produced by a co-current, one-stage pilot plant spray dryer with a maximum water evaporation rate of 30 kg/h. The amount of surface oil and the oxygen diffusion pathway were modified by altering the homogenization pressure and emulsifier concentration. The size distribution of oil droplets within the powder was assessed by time domain nuclear magnetic resonance. Samples were stored at 25°C for 8 weeks in the dark and primary oxidation products were determined in form of hydroperoxides. Apart from the overall hydroperoxide concentration of the powders, the concentration within the surface oil and within the encapsulated oil was assessed separately. For the encapsulated oil, surface oil removal occurred at two different points, before storage and before measuring.

The simulation was conducted using COMSOL Multiphysics®. The reaction kinetic of lipid oxidation was determined by measuring the hydroperoxide formation of lipids stored at atmospheres of different oxygen concentrations. The model geometry of an encapsulated lipid particle was generated using LiveLink™ for MATLAB®. The oxygen diffusion and hydroperoxide formation were simulated using the Chemical Reaction Engineering Module, specifically with the Transport of Diluted Species and Chemistry interfaces. In a parametric study the impact of surface oil, the physical properties of the wall matrix, oil droplet size, particle size and oil content were evaluated.