Crystallisation behaviour of palm oil nanoemulsions carrying vitamin E

Abstract

Four emulsions were prepared using high pressure homogenisation at 300 or 1200 bar and aqueous phases containing 4.5 wt% whey proteins in mixture with 20 wt% palm oil (PO), alone (E300 and E1200), or in which 20 wt% PO was replaced by vitamin (EV300, EV1200). Thermal behaviour of bulk fat and emulsions in the absence or presence of vitamin, as monitored by differential scanning calorimetry (DSC), indicated that fat crystallisation in supercooled melt was delayed in bulk fat in the presence of vitamin and more delayed in emulsions with lower droplet sizes and containing vitamin. These results were supported by (i) isothermal DSC experiments where exothermic peaks occurred at higher holding times and (ii) dynamic DSC experiments which showed lower melting reactions in emulsions with lower droplet sizes and containing vitamin. Synchrotron X-ray scattering measurements performed simultaneously at small and wide angles on fat samples stored at 4 °C for 12 h showed co-existence of 2L and 3L longitudinal stacking in bulk fat without vitamin, and only 2L organisation of TAGs in the presence of vitamin. Trends in the proportions of α, β′, β lateral packing in lipid droplets were also observed to be more affected by the presence of vitamin rather than their size, indicating a higher rate of α → β′ → β polymorphic transformations in the presence of vitamin. Combining data obtained from DSC and X-Ray signals showed that lipid droplets with lower solid fat content, of which a higher proportion of β polymporphs, were those presenting lower size and lower ability for vitamin protection against chemical degradation, which is of great interest for formulation of lipid nanoparticles as bioactive matrix carriers.