Polyunsaturated n-3 fatty acids are pro-healthy diet component. Linseed is one of the richest and easily available source of n-3 α-linolenic acid. Unfortunately, this valuable fatty acid can be easily oxidized through auto-oxidation, photooxidation or enzyme-catalysed reactions. Encapsulation can protect the PUFAs against oxidation by shielding them against oxygen and also hiding any unwanted flavours from the raw material.
The aim of this study was to compare selected physical and chemical properties of prepared emulsions and encapsulated powders containing linseed oil (LO) and its ethyl esters (LE) prepared with the use of the most popular coating materials, such as whey protein concentrate (WPC), Arabic gum (GA), and maltodextrin (M). Powders were prepared by spray- (SD) and freeze-drying (FD) methods. Comparison was done based on emulsions (morphology, particle size distribution, stability), and powders (morphology, physicochemical properties, oxidative stability and fatty acid composition) properties.
The emulsions containing M and GA were characterized by a monomodal particle distribution. In the case of the sample containing LE, there was one major fraction of particles in the range of 1.44-17.38 μm and they were droplets of the dispersed oil phase. The image of the emulsion microstructure shows that the particles of the dispersed phase do not tend to agglomerate and coalesce. In turn, the image of a sample containing LO reveals the presence of agglomerates in the microstructure of the emulsion composed of several droplets of the oil phase of relatively large size. In contrast, emulsions consisting of M with WPC had a bimodal distribution. In the case of the sample containing LE, two fractions are clearly visible. The first fraction is in the range of 0.04-0.95 μm and consists mainly of protein particles. The particle size of the second fraction is in the range of 1.09-15.13 μm and they were droplets of the dispersed oil phase and protein-oil agglomerates. The turbidimetric analysis of the stability of the emulsion samples showed that the emulsions prepared with the use of WPC were characterized by lower stability compared to the emulsion samples containing GA. In LO M GA, LE M WPC, and LO M WPC samples we can observe the phenomenon of separation of the dispersed phase by creaming, with this being the strongest in LO M WPC sample. The FD samples were characterized by very good wettability. The determination of solubility in all samples showed that a precipitate is formed only in preparations containing WPC, regardless of whether the powder sample was from FD or SD drying. FD powders contained M and WPC had a much higher surface oil content (10.95 and 11.48 % d.m.) compared to powders containing M and GA (4.42 and 5.52 % d.m.) and regardless of the coating ingredients of the SD powders (6.78-8.78 % d.m.). The SD powders had greater oxidative stability index (2.26-7.16 h) compared to FD powders (0.49-1.79 h). While only SD powders showed higher stability compared to LO (2.44 h) and LE (1.30 h). Regardless of the drying method used and the composition of the emulsion, no significant effect on the fatty acids composition was observed.