| Lycium barbarum belongs to the plant family Solanaceae, which has purple flowers, redfruit and leafy. Fruits of Lycium barbarum have been used as a traditional Chinese herbalmedicine for thousands of years, which play an important role in nourishing the liver andkidney and brightens the eye and as early as two thousand years ago which has beendocumented and listed as the top grade in the "Shen Nong’s Herbal classic ". In recent years,modern studies also found that Lycium barbarum possess a range of pharmacological effects,including regulating immunity, inhibiting tumor growth and cell mutation, anti-aging and fattyliver. Lycium barbarum polysaccharides (LBP) as one of the main pharmacologicalcomponents, the studies indicated LBP have a good effects on enhancing immunity,anti-cancer, anti-aging, protecting the optic nerve, preventing apoptosis.For LBP extractionand separation, however, the mainstream of most enterprises still follow the traditionalproduction process of hot water boiling method, which exists some fundamental flaws inlong-time extraction, high energy consumption, low extraction efficiency.Subcritical water is the temperature of water above100oC and below374oC, a pressureto keep the liquid state, also known as the high pressure hot water or hot liquid water.Generally, water is polar compounds. However, under the505KPa pressure, with temperaturerise (50~300oC), its dielectric constant decreases from70to1, meaning that its propertiesgradual changes from strong polarity to non-polar, effective components can be extractedaccording to the polarity from high to low.Since subcritical water is a technique based on theuse of water as extractant at high temperature and high pressure, which not need add acid,alkali or other catalyst, so the extraction method is referred to as "green treatment". Since theadvent of the technique, it has become a research hotspot in the sector of extraction separationdue to continuous extraction, a shorter extraction time, high efficiency, cheap accessible andenvironment friendly advantages, but some heat-sensitive components or macromoleculessubstances are prone to occur irreversible changes at a high temperature, which limited itswild application.In order to overcome the drawback, the Lycium barbarum polysaccharide (LBP) were used as the studied objects and the extractive yield of LBP as the indexes in this dissertation.On the basis of the apparatus of subcritical water extraction has been designed successfully, aphysical means was applied to enhance the extraction procedure of subcritical water byintroducing an ultrasound wave into the extraction kettle. LBP extracted by subcritical waterand ultrasound-enhanced subcritical respectively, to study the impact of extractiontemperature, extraction time, extraction pressure, liquid-to-solid ratio, and ultrasonic poweron LBP extraction yield; Then response surface method in combination with theBox-Behnken design was used to optimize the extraction process; Besides, the comparisonamong hot water extraction (HWE), ultrasound extraction (UE), subcritical water extraction(SWE) and ultrasound-enhanced subcritical water extraction (USWE) in terms of LBPextraction yield, the chemical composition of the crude LBP, antioxidant activity as well ascellular immune activity were also studied. Finally, the mathematic model of USWE was builtand ultrasonic enhance mechanism was researched.The results show that extraction temperature, extraction time, extraction pressure,liquid-to-solid ratio all can effect the LBP extraction yield by SWE and USWE, and under thesame condition, the ultrasound can significantly improve efficiency. The optimal extractioncondition of USWE was extraction temperature of100oC, extraction time of53min,extraction pressure of5MPa, liquid-to-solid ratio of26∶1(mL/g), ultrasonic power of160W.At this optimum condition the LBP extraction yield was5.73%.As for the four extraction methods, under the similar condition, extraction temperature of100oC, extraction time of80min, extraction pressure of5MPa, liquid-to-solid ratio of30:1(mL/g), ultrasonic power of160W, the results show the maximum LBP extraction yield up to5.57%was extracted by USWE, followed by SWE was4.99%, again by UE and HWE was4.18%and3.82%respectively. Preliminary chemical compositions were conducted, whichresults demonstrated that the content of basic chemical composition of the fourpolysaccharides was also a little different without regularity, and the LBP extraction by SWE(LBP-S) and USWE (LBP-US) may be contains more deep pigments and other impurities.High performance gel permeation chromatography (HPGPC) of crude LBP shown that crudeLBP extracted by UE (LBP-U) only had one fraction but others have two, which might be dueto the higher ultrasonic power (360W) used in that extraction method that made the polysaccharides become homogenous. The antioxidant activity assay revealed the significantantioxidant activities of four polysaccharides. It was found that the antioxidant capacity ofLBP-US was significantly higher than those of LBP-H, LBP-U, and LBP-S and followed theorder: LBP-US> LBP-S> LBP-H> LBP-U. Immunomodulatory activity test exhibitedremarkable macrophage-activating by the macrophage cells proliferation, phagocytosis andNO production. Moreover, the results of mice liver image and liver index show the LBP-UScan reduce blood fat and protect liver at some degree, which still need further research.Based on the characteristics of a closed system of high temperature and high pressure inthe subcritical water system, which is meet Fick’s second law, and considering the ultrasonicvibration effect in subcritical water, a dynamic model of ultrasonic enhance subcritical waterextraction was built. Ultrasonic cavitation effect as the main enhance mechanism was studied,such as the cavitation bubble of kinematics equation also be built, the effect of temperatureand pressure on the kinematics of cavitation bubble process were analysed and the cavitationyield was measured by iodometry. The results declare the cavitation yield increases with therise of temperature, and decreases with the increase of pressure which suggest the ultrasoniccavitation effect can enhance subcritical water extraction. |
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