The Stability Of Carotenoids Under Ultrasond-assisted Extraction And Quantitative Structure-activity Relationship Of Carotenoids

Carotenoids are a family of natural pigments which are always from fruits and vegetables in diets. Some of carotenoids are one part of human tissues and organs. For example, lutein is one part of macula of the eye. Some of carotenoids are the main dietary sources of Vitamin A. And carotenoids are associated with the reduction in the incidence of cancer, age-related macular degeneration, antioxidant activity, osteoporosis, photoprotection and cardiovascular diseases. The well-known antioxidant activity has been suggested to be the main anticancer mechanism of carotenoids, gap junctional communication (GJC) is possible the other anticancer mechanism of carotenoids. The largest number of carotenoids found in any fruit are those of citrus fruits:more than 115 different compounds. The peels of citrus are an abundant source of natural carotenoids. However, seldom studies on extraction and utilization of carotenoids in citrus peels are reported. Ultrasound-assisted extraction has high extraction efficiency, low extraction temperature, simpler and economically cheaper equipment.The objective of this study was to determine the degradation mechanism and extraction principle of all-trans-β-carotene from citrus peel under ultrasound-assisted extraction (UAE), was to develop quantitative structure-activity relationship (QSAR) models for the anticancer activity based on the data.The main results and conclusions were listed as follows:1. The effects of factors under ultrasound treatment on the stability of all-trans-β-carotene in a model system were investigated. The type of solvents and temperature were important factors in determining the degradation reaction. Liquid height, ultrasonic intensity and duty cycle of ultrasound exposure only affected the rate of degradation but did not change the nature of degradation. Degradation rate of all-trans-β-carotene in dichloromethane was the highest. Degradation rate of all-trans-β-carotene decreased with increasing of temperature, which is inconsistent with Arrhenius theory. All-trans-β-carotene concentration firstly decreased markedly, then increased slightly with liquid height. All-trans-β-carotene concentration firstly decreased, then increased, lastly did not changed significantly with ultrasonic intensity. All-trans-β-carotene concentration firstly decreased significantly, then increased significantly with the increasing duty cycle.2. Degradation mechanisms of all-frans-β-carotene in different temperatures were different. Degradation kinetics of all-trans-β-carotene under ultrasound fitted first-order reaction at-5 to 15℃, and fitted second-order reaction at 25℃. Degradation products at-5 to 15℃included isomers:15-cis-β-carotene,di-cis-β-carotene and other compounds with function group of C-O. Degradation products at 25βincluded isomers:15-cis-β-carotene, di-cis-β-carotene. In addition, A new method to produce isomers ofβ-carotene was obtained according to the degradation mechanism.3. The ultrasound extraction principle of all-trans-β-carotene was comprehensively investigated. The advantage of extraction yield under ultrasound in comparison of under maceration was attributed to the particle size. Solvent of dichloromethane caused the degradation of all-trans-β-carotene extracted during UAE. Solvent of ethanol showed a pronounced higher extraction yield during UAE in comparison of maceration. It can be concluded the polar solution-ethanol can be used to exraction the nonpolar molecules under ultrasound extraction and ultrasound extraction principle is different to the maceration principle of "Like dissolves like" The extraction yield of UAE had a peak value at 25℃. The extraction yield of UAE did not easily arrived equilibrium in comparison of maceration. The extraction yield increased first, then decreased, then slightly increased with increasing of ultrasonic intensity. The extraction yield of UAE decreased with increasing of liquid height. The extraction yield increased with increasing of duty cycle until equilibrium. Pulsed ultrasound extraction ofβ-carotene with the solvent of ethanol may be a green and low carbon method.4. Quantitative structure-activity relationship (QSAR) models of antioxidant activity were developed using stepwise regression and multilayer perception neural network based on calculated descriptors of quantum chemistry. The results showed that the significant molecular descriptor related to the antioxidant activity of carotenoids was the energy gap between the highest occupied molecular orbital energy (EHOMO) and the lowest unoccupied molecular orbital energy (ELUMO). The two models of antioxidant activity both showed good predictive power, but the predictive power of the neural network QSAR model of antioxidant activity was better.5. Quantitative structure-activity relationship (QSAR) models of gap junction communication activity (GJC) were developed using stepwise regression and multilayer pere(?)tion neural network based on calculated descriptors of quantum chemistry. The molecular descriptor related to the GJC was the lowest unoccupied molecular orbital energy(ELUMO).The two GJC models had similar, moderate predictive power.The current study should be very useful for the application of ultrasound extraction and explained the anticancer mechanism of carotenoids from the chemical point of view.