Formation of physically and chemically stable
delivery systems for bioactive compounds is a key challenge for food and
pharmaceutical industries. Solid lipid nanoparticles (SLN) and nanostructured
lipid carriers (NLC) have emerged as potential structures to encapsulate
unstable lipophilic bioactives. We hypothesized that by selecting appropriate
surfactants (high- or low melting lecithin) we can control the crystallization
behavior of the lipid nanoparticles, resulting in entrapment of ω-3 fatty acids inside the solid lipid matrix
thereby preventing their oxidation. Therefore, we investigated the influence of
surfactant type on physical and chemical stability of (i) NLC containing
tristearin and ω-3 fish oil, (ii)
tristearin SLN, and (iii) ω-3 fish oil-in-water
emulsions. The physical and chemical stability of the nanoparticles was
evaluated by light scattering, differential scanning calorimetry (DSC), gas
chromatography, and cryo-transmission electron microscopy (TEM). Results showed that the presence of fish oil reduced the
crystallization temperature, melting temperature, and melting enthalpy of
tristearin. NLC stabilized with high melting lecithin inhibited the oxidation
of ω-3 fatty acids ≥ 90%
compared to those stabilized with low melting lecithin. This was attributed to the solidified surfactant layer of high melting lecithin inducing
crystallization of the shell by interfacial heterogeneous nucleation. In
contrast, low melting lecithin does not solidify before the tristearin and thus
cannot control the crystallization behavior. This leads to disordered crystals
structure and partial or full expulsion of the liquid ω-3 fatty acids. The results demonstrated that oxidation
of unstable ω-3 fatty acids
encapsulated in lipid nanoparticles was inhibited by the creation of an
appropriate crystal structure - without the use of antioxidants. Our findings indicated that the
saturated high melting lecithin was the key in controlling the crystallization behavior. This study shows that
structure design can be used to control chemistry in a major way.
Principal
investigator: Prof. Jochen Weiss j.weiss@uni-hohenheim.de
