| : Carotenoids, one class of natural pigments, are ubiquitous in the world of plant and animal organisms. They are red, yellow or orange in color. In the past few years only plants or microorganisms could synthesize this kind of natural biomaterials. Carotenoids can interact with proteins, DNA, polysaccharides and other biomolecules, playing diverse functions, which include light harvesting, photo protection, stabilization of cell membrane, and prevention of some chronic diseases. One of very important carotenoids is lycopene (C40H56), which is mainly found in ripe tomatoes and tomato-based food products. Lycopene has a 40-carbon, open hydrocarbon chain including eleven conjugated and two non-conjugated double bonds arranging in a line array. Since lacking -ionone ring in its molecular structure, lycopene has no any activity of provitamin A. As a natural antioxidant, however, lycopene plays some important roles on human beings and animals due to its significant ability to prevent against some cancers and cardiovascular diseases. Moreover, lycopene and its some metabolites can modulate the intercellular gap junction communication. Because of the presence of a long chain of conjugated carbon-carbon double bonds, lycopene is susceptible to degradation and isomerization when exposed to light, heat or oxygen. For human beings and animals, the isomerization of lycopene also happens during the process of absorption and metabolism. In this paper, the physicochemical properties and its interaction with polysaccharides were studied experimentally and theoretically. The main results are as follows.1. Lycopene was extracted from tomato paste and purified further, then characterized qualitatively and quantitatively by HPLC, FTIR, UV/Vis absorption spectroscopy, and DSC. The content of lycopene samples obtained were found to be between 94% -96%, which laid a foundation of investigation on lycopene properties.2. The thermal degradation and isomerization of lycopene are related to its potential health benefits and nutritive value. Lycopene isomerization and degradation easily happen during heating process. The kinetics of isomerization and degradation for lycopene in soybean oil during heating were studied experimentally in order to provide the basic data for the optimization of processing technology of lycopene products. The sample of all-trans lycopene was heated in soybean oil at 70, 80 and 90 C, respectively. The concentrations of lycopene were determined by means of UV/Vis absorption spectrometry. It was found that the main reaction was isomerization (from all-trans isomer to cis-isomers) in the first period and then was degradation. Furthermore, the isomerization and degradation of lycopene followed a first-order kinetic model. The isomerization rate constants were 1.74 10-3, 4.96 10"3 and l.02 10-2min'1) at 70, 80 and 90C. The apparent activation energy of isomerization was calculated to be 93.1kJ/mol. The degradation rate constants were 3.6310-3, 4.45 10-3 and 7.01 X 10-3(h-1) at 70, 80 and 90C and the apparent activation energy was 34.3kJ/mol.3. The structural and electronic properties of various lycopene isomers, such as geometry, energy, frontier orbits and electronic transition spectroscopy, were investigated theoretically based on density functional theory (DFT). The calculation of quantum chemistry model was performed by B3LYP with the 3-21G* basis set. The relationship between lycopene molecular structure and its biological activity was analyzed. The structures optimized show that, while the central conjugated part of every lycopene isomers is planar or nearly planar, the two terminal positions are rotated out of plane and the conjugated double bonds also lightly deviate from the coplanarity, especially for the cw-double bands of cw-isomers. The increase in bondlength of cis-double bonds and the electron cloud extending result in weakening of -bond, which indicates the enhanced reactivity of bonds related to trans-cis isomerization.The energy difference, lumo - homo , between the LUMO and HOMO determin...
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