| Summary: | 碩士 === 輔仁大學 === 食品科學系 === 95 === Lycopene, one of the major carotenoids, is naturally present in an all-trans form in vegetables and fruits. With a long chain conjugated carbon-carbon double bonds, lycopene possesses antioxidative and free-radical scavenging abilities, and reduces the risk of cancers. Its biological activity may decrease when lycopene is thermally isomerized or oxidatively degraded under light exposure. Therefore, nano-encapsulated lycopene (NPL) was developed to protect it from environmental damage. The objectives of this study are to evaluate the stability of nanocapsules（NPs）and submicron-capsules （SPs）and study the kinetics for thermal and oxidative degradation of lycopene in NPs. Dynamic light scattering analysis showed that the average particle diameters were 2.75, 7.51 and 11.35nm for single-coated, double-coated and multiple-coated NPs, respectively. Among these, multiple-coated NPs had the highest stability. When diluted 100-fold with a phosphate buffer, NPs ranging from 11.1-11.3nm, were not significantly different in diamerters at pH 3.5, 6.0 and 6.8. The above diluted NPs maintained its stability at pH 3.5 and 6.0 for 2 and 1 hr, respectively. However, at pH 7.4 aggregated NPs were found and the average diameter was significantly reduced to a low level. Similarly, the average diameters of diluted SPs, ranging from 432.05-444.25nm, were also not significantly different at pH 3.5, 6.0 and 6.8, but significantly reduced in particle size at pH7.4. Results of differential scanning calorimetry indicated that NPs and SPs had the thermal stability up to 130℃ at both pH 3.5 and 6.0. On the contrary, both NPs and SPs were unstable at pH 6.8 and 7.4. When lycopene in the crude extract（LE）and NPL were heated with nitrogen purging, the rate constants for lycopene degradation were observed as follows: thermal degradation of cis-lycopene > thermal degradation of all-trans-lycopene > isomerization. As the heating temperature increased from 60℃ to 120℃, thermal degradation of cis-lycopene increased 10.7-fold, whereas thermal degradation of all-trans-lycopene only increased 2.7-fold. Thus, all-trans-lycopene was more thermally stable than its cis-isomers. When LE and NPL were heated with oxygen purging, the rate constants for lycopene degradation were observed as follows: thermally oxidative degradation of all-trans-lycopene > thermally oxidative degradation of cis-lycopene > isomerization. Above results showed that the rate constants for thermally oxidative degradation increased with increasing heating temperature. Under heating with nitrogen, the thermal degradation and isomerization rates constants for LE were found to be 1.1-2.6 times higher than those for NPL, indicating that inhibition of thermal degradation and isomerization reactions due to nano-encapsulation was only slightly reduced. On the other hand, thermally oxidative degradation rates constants for LE were 10.9-24.0 times greater than those for NPL, denoting that nano-encapsulation could effectively inhibit the oxidative reaction during heating with oxygen. For various reaction constants analyzed by linear and nonlinear regressions, all the correlation coefficients were higher than 0.915, expect for the heating of NPL at 90℃with oxygen purging （r2 = 0.858）. The kinetic model developed in this study can be used to predict the concentration changes of degradation and isomerization of lycopene in both LE and NPL.
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