Characterisation of thermal and structural behaviour of lipid blends composed of fish oil and milkfat.

The blend of fish oil with a high percentage of long chain poly-unsaturated fatty acids, and milkfat with a high percentage of saturated fatty acids, could potentially demonstrate desirable characteristics from both components, such as increased omega-3 fatty acids and melting point, as well as improved crystallization and oxidative stability. In this study, the effect of various milkfat concentrations on thermal properties and crystalline structure of these blends were analysed to understand parameters determining the overall characteristics of the blend. Blends with different ratios of fish oil: milkfat (9:1, 7:3, 5:5, 3:7, 1:9), as well as pure fish oil and pure milkfat, were investigated at different cooling conditions. The crystallization behaviour in all samples shifted to lower temperature ranges, by increasing the cooling rate from 1 to 32 °C/min. However, the changes in cooling rate did not have significant effect on the melting profile of the samples. Whereas changes in milkfat ratio affect both the crystallization and melting behaviour. New crystallization peaks were observed on DSC spectra between the range of -4 to -13 °C in the blends. Moreover, new melting peaks appeared in two ranges of -1 to -8 °C and 8-9 °C, in the blends. The crystallization and melting behaviour of the blends were similar to those of milkfat when >30% milkfat was used. This was further confirmed via XRD where milkfat demonstrated the dominant polymorphic behaviour. Regarding shape of the crystals, fractal dimension analysis showed a similarity between clusters in blends containing 50% milkfat or higher. Increasing the ratio of milkfat led to an increase in fractal dimension which indicates higher mass-spatial distribution of the crystal networks in the blends. The data showed that adding 30% or more milkfat to pure fish oil resulted in blends demonstrating similar characteristics to milkfat, including thermal, structural, and oxidative stability. This shows the potential of blending a high percentage of docosahexaenoic acid in milk fat to improve their overall stability.