Influence of lipid nanoparticle physical state on β-carotene stability kinetics under different environmental conditions

Carotenoids are lipophilic compounds that provide important health-related benefits for human body functions. However, they have low water solubility and chemical stability, hence their incorporation in aqueous-based foods requires the use of emulsion-based lipid carriers. This work aimed at elucidating whether their inclusion in emulsion-based Solid Lipid Nanoparticles (SLNs) can provide a protective effect against beta-carotene degradation under different environmental conditions in comparison to liquid lipid nanoemulsions. Glyceryl Stearate (GS) was mixed with Medium Chain Trygliceride (MCT) oil to formulate SLNs. SLNs presented a significantly enhanced beta-carotene retention and a slower beta-carotene degradation kinetics at increasing storage temperature, acidic conditions and light exposure. In fact, SLNs formulated with 5% GS in the lipid phase and stored at 4 degrees C and pH 7 retained almost 70% of the initially encapsulated beta-carotene after 55 days of storage, while it was completely degraded when it was encapsulated in liquid nanoemulsions. Moreover, it was observed that the solid lipid type affects the protective effect that SLNs may confer to the encapsulated lipophilic bioactives. Saturated long chain triglycerides, such as hydrogenated palm oil (HPO) presented slower and lower beta-carotene degradation kinetics in comparison to solid lipids composed of MCT, such as Coconut Oil (CNUT) or MCT + 5% of GS in the lipid phase. This work evidences that the incorporation of lipophilic bioactive compounds, such as beta-carotene, into SLNs slows down their degradation kinetics which might be attributed to a reduced diffusion of the oxidative species due to the lipid crystalline structure.