| Litchi (Litchi Chinensis Sonn.), called fruit king of south China, is a world-wide famous fruit. China is the first country planting litchi in the world. There are more than one hundred of cultivars in China. In 2005, the yield and planting area in China are 1,650,000 tuns and 600,000 hectares, accounting for 70.5% of total yield and 84.5% of total area in the world, respectively. The pericarp tissues account for 16% of total weight of litchi fruit. They enrich in flavanols and water-soluble polysaccharides, and can be employed to produce healthful food and medicine. But, during the programme of direct consumption and agro-industrial process, litchi pericarp is eliminated as waste. Therefore, further development of this material means much for improving the by-product value of litchi fruit, facilitating the development of related agro-industry and enviroment protection.Six well-known litchi cultivars (Huaizhi, Baila, Sanyuehong, Feizixiao, Nuomici and Guiwei) were chosed in this project. The total flavonoid content, water-soluble polysaccharide content and in vitro antioxidant activities were determined. The results showed Huaizhi litchi pericarp had the highest total flavonoid content and water-soluble polysaccharide content with the value of 32.16 mg/g and 5.51 mg/g, respectively. The antioxidant activities of crude flavonoids from these six cultivar were not significantly different. Thus, Huaizhi was selected for the following trials.In the experiments of developing the extraction program of flavonoids from litchi pericarp tissues, the effects of solvent (water, 60% (v/v) of ethanol solution and ethyl acetate), hydrochloric acid, extraction time, extraction temperature, solvent-material ratio, ethanol solution concentration and extraction times on extraction program were studied. Response surface methodology was further taken basing on the single factor experiments. Extraction time, extraction temperature, solvent-material ratio and ethanol solution concentration were chosed in this programme. The mathematic model was built between the response, total flavonoids yield, and four factors. The interactions between every two factors were analysed. The optimal conditions for obtaining the highest total flavonoid yield were as follows: 3.9h of extraction time, 78.2℃of extraction temperature, 20.0 ml/g of solvent-material ratio and 80.0% of ethanol solution concentration.In the experiments of isolation and purification of crude flavonoids, they were classified into four fractions depending on solubility by hexane, ethyl acetate, butanol and water. The ethyl acetate phase was chosen for further purification for its high total flavonoid content and antioxidant activity. Three compounds were isolated and collected by reverse-phase high performance liquid chromatography (HPLC). They were identified as epicatechin, proanthocyanidin B2 and proanthocyanidin B4 by HPLC-mass spectrometry, nuclear magnetic resonnance spectrometry and ultraviolet-visible light spectrophotometer.In vitro trials of determination of antioxidant activities, immune cell proliferation and breast cancer cell proliferation were made. The results showed these three flavanols had strong radical-scavenging activities. The ethyl acetate fraction and epicatechin had significant capacities of promoting spleen lymphocyte proliferation. Epicatechin and proanthocyanidin B2 had significant capacities of inhibiting breast cancer cell proliferation, though lower than that of paclitaxel.Four factors, extraction time, extraction temperature, water-material ratio and extraction times, were selected for exploring the water-soluble polysaccharide extraction process. Response surface methodology was taken to optimize the process conditions basing on single factor trials. Extraction time, extraction temperature and solvent-material ratio were set. The mathetical model of water-soluble polysaccharide yield as a function of extraction time, extraction temperature and solvent-material ratio was built. The interactions between factors of each other were analysed and the optimal conditions for obtaining highest water-soluble polysaccharide yield were computed as follows: 2.7 h of extraction time, 75.1℃of extraction temperature and 13.8 ml/g of solvent-material ratio.Even-molecular-weight water-soluble polysaccharides were obtained by using techniques of DEAE anion-exchanging chromatography and gel filtration chromatography. It comprised mannose (65.6%), galactose (33.0%) and arabinose (1.4%). The molar percentage ratio of (1→2)-glycosidic linkages, (1→3)-glycosidic linkages and (1→6)-glycosidic linkages was about 8.7%:83.3%:8.0%. The molecular weight was determined as 14 kDa by gel permeation chromatography. The infra-red spectra showed mannose existed asβtype. By comparison of antioxidant activities of water-soluble polysaccharides from each purification step, we found that the antioxidant activity kept increasing as purification went on.
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