Nanostructures and polymorphisms in protein stabilised lipid nanoparticles, as food bioactive carriers: contribution of particle size and adsorbed materials

Eight oil-in-water emulsions were prepared using melt high-pressure homogenisation (HPH) at 300 or 1200 Bar. The emulsions produced from lipid phase (20%) were composed by palm oil alone or in mixture with α-tocopherol at 4:1 weight ratio, and an aqueous phase containing whey proteins alone or in mixture with phospholipids. The resulting nanoemulsions (fat droplet size ranging from 200-500 nm) presented different stability against aggregation and coalescence, fat crystallinity and polymorphisms in relation to different degrees of α-tocopherol encapsulation and protection against chemical degradation. Protein stabilised emulsions were monomodal, while emulsions stabilised by proteins and lecithins were slightly bimodal. Application of an isothermal treatment (4 °C for 2 hours) to these emulsions showed crystallization peaks located at longer time values in smaller particle size emulsions, while in the presence of added α-tocopherol average particle size values were higher and crystallization was not observed in 2 hours storage. Study of fat polymorphisms performed after 12 hours storage at 4 °C revealed the formation of 2L structures with coexistence of α, β’ and β forms in all of the emulsions. Increasing HPH from 300 to 1200 Bar favoured development of β structure (4.5 A-1) in α-tocopherol added emulsions, with the presence of one extra peak β structure evolved at 3.9 A-1 only in emulsions containing lecithins. α-tocopherol addition decreased in 2L structures (by approx. 40-50%). The formation of lipid nanoparticles with decreasing size values (increasing HPH parameters) was accompanied by increased long-term stability against aggregation and coalescence, but increased vitamin degradation (up to 15 wt% for 1200 bar). Degradation of α-tocopherol after 2 months storage at 4 °C was lower for nanoparticles stabilised by whey proteins alone (21 and 33%, respectively) than for nanoparticles stabilised by whey proteins in mixture with phospholipids and presenting higher size values (44 and 52%, respectively), where β polymorphs were more evolved.