Improving the chemical stability of beta-carotene and citral by nanoemulsions

In this study, various nanoemulsion formulations were prepared to encapsulate non-polar beta-carotene and partly polar flavor molecule citral.;For the encapsulation of beta-carotene, the nanoemulsion core material was a mixture of both solid lipid (palm kernel fat) and liquid oil (medium chain triglyceride, MCT). Aqueous nanoemulsion dispersions were obtained by the combination of high speed and high pressure homogenization processes and the solid nanoemulsion powders were also obtained by lyophilization using sucrose as the cryoprotectant. For the aqueous dispersions, the formulation using pure palm kernel fat as the lipid phase was the best one to protect beta-carotene from degradation. For the freeze-dried samples, the incorporation of liquid MCT oil is necessary to disturb solid lipid crystallization to protect beta-carotene. The in vitro digestion experiments were performed to evaluate the bioaccessibility of beta-carotene in palm kernel fat nanoemulsion and MCT nanoemulsion; the results showed that the bioaccessibility of beta-carotene was greatly improved after encapsulation. The palm kernel fat had better performance than the MCT to release beta-carotene from the nanoemulsion formulations.;For the encapsulation of citral, two strategies were developed to improve citral stability at acidic condition (pH = 3.0). The first strategy was to incorporate six different natural antioxidants (black tea extract, ascorbic acid, naringenin, tangeretin, beta-carotene and tanshinone) with citral together in the palm kernel fat nanoemulsions. The second strategy was to construct multilayer nanoemulsions to encapsulate citral. The multilayer emulsions were prepared by the layer-by-layer deposition technique between oppositely charged emulsion droplets and two polymer coatings: chitosan (CS) and epsilon-polylysine (EPL). The stability of citral as well as the production of the off-flavor compounds was analyzed by solid phase microextraction gas chromatography (SPME-GC). The results suggested that encapsulation of citral in combine with the appropriate antioxidants (beta-carotene, tanshinone and black tea extract) could greatly enhance citral's chemical stability during storage; and the additional cationic chitosan interfacial layer was also effective to improve the stability of citral.