E/Z Isomerization Of Lycopene Catalyzed By Iodine-Nanoparticles And Lycopene-Loaded Nanostructured Lipid Carriers

Lycopene, as an important and bioactive carotenoid, has attracted considerable attention due to its multiple potential protective effects against various chronic diseases. Many recent studies have demonstrated that more than 90% of natural lycopene in most food sources is present primarily as the（all-E）-form and its biological activity is lower than that of（Z）-lycopene isomers. Therefore, highly efficient heterogeneous catalytic E/Z isomerization of lycopene was separately achieved using two kinds of iodine-doped titanium dioxide（I-TiO₂） catalysts. On the basis of this study, the stability and bioavailability of lycopene isomerized products were investigated, and lycopene-loaded nanostructured lipid carriers（Lyco-NLC） were also prepared. The aim of this work was to improve the stability, biological activity and bioavailability of lycopene. Main research contents include:1. Amorphous I-TiO₂ catalyst was prepared by modified sol-gel method, using tetrabutyl titanate as precursor, potassium iodate as iodine source. The catalyst was characterized by XRD, BET and SEM et al., and the effect of the main factors on the catalytic isomerization of lycopene was investigated using the total cis-ratio of lycopene as an index. The catalyst was formed by the organic carbon compound, wrapping anatase phase TiO₂ particles and negative iodine ions（I–） having an important catalytic activity. Application tests showed that the catalyst was highly active in the isomerization of lycopene in heterogeneous reaction, and the total cis-ratio of lycopene exceeded 75% after 2 h of reaction at 75 °C in ethyl acetate. Moreover, the catalyst displayed 89% of retention activity after five reuses. This study provides a highly efficient route for the production of lycopene products with high cis-ratio.2. In order to make up the deficiency of the amorphous I-TiO₂ catalyst, the crystal I-TiO₂ catalyst was prepared by modified hydrothermal method, using tetrabutyl titanate as precursor, potassium iodate as iodine source. The catalyst was characterized by XRD, BET and SEM et al., and the effect of the main factors on the catalytic isomerization of lycopene was investigated using the conversion and selectivity of lycopene as indexes. The results showed that the existence of negatively charged iodine（I–） species would be dispersed on the surface of the anatase mesoporous TiO₂ particles or at the interstitial sites of the TiO₂ lattice. Application tests showed that the nonselective catalyst was highly active in the isomerization of lycopene in heterogeneous reaction, and the conversion of all-trans-lycopene exceeded 80% after 2 h of reaction at 75 °C in ethyl acetate. Moreover, the catalyst displayed 84% of retention activity after five reuses. On the basis of this study, the plausible reaction mechanism to explain the role of the crystal I-Ti O2 was preliminarily discussed. This study further provides a highly efficient route for the production of lycopene products with high cis-ratio.3. The storage stability and degradation kinetics of isomerized lycopene products were investigated, and the results showed that the degradation process of 78.5% cis-ratio of lycopene can be regarded as a pseudo first order reaction; with the increase of temperature, the degradation of lycopene was accelerated; from the apparent activation energy point of view, the stability of the 5Z isomer was the most stable among the lycopene isomers; the stability of the prepared 78.5% cis-ratio of lycopene was slightly higher than all-trans lycopene. Moreover, lycopene samples with a series of total cis-ratios were prepared, and the bioaccessibility of these samples was estimated using a diffusion model, the results showed that the bioaccessibility of lycopene markedly increased conforming to a linear regression model with increasing of the total cis-ratio of lycopene, the ratio of bioaccessbility for 100% to 0% total cis-ratio of lycopene was calculated as approximately 5. Furthermore, the specific role of the microstructure and melting point of 3.6% and 78.5% total cis-ratio of lycopene was also investigated to understand the probable mechanism for the enhanced bioaccessbility of（Z）-lycopenes. The results showed that the external structure of 3.6% total cis-ratio of lycopene demonstrated a needle-like crystalline texture, whereas the 78.5% total cis-ratio of lycopene demonstrated a spherical granule-like amorphous texture with much smaller size. The melting point of 78.5% total cis-ratio of lycopene was observed a decrease of 26.65 °C by comparing that of 3.6% total cis-ratio of lycopene.4. Lycopene-loaded nanostructured lipid carriers（Lyco-NLC） were prepared by melting-preemulsification and high pressure homogenization. On the basis of the encapsulation efficiency, loading capacity and retention rate as the evaluation indexes, the preparation and physical and chemical stability of Lyco-NLC were investigated. The storage tests of Lyco-NLC were carried out during 30 d at 20 oC in darkness, and the results showed that the average particle size distribution was in the range of 199²36, PDI values were less than 0.3, the retention rate of lycopene exceeded 77%, and the prepared Lyco-NLC had good physical and chemical stability. The structure of Lyco-NLC was characterized by atomic force microscopy, transmission electron microscopy, X- ray diffraction and Fourier transform infrared spectroscopy et al., the results showed that the particle in Lyco-NLC was a kind of spherical structure, and lycopene molecular was dispersed into the non-perfect lattice system which was composed of solid and liquid lipid.