Rheological Properties, Structure Identification And The Avtivity Of Scavenging Radicals Of Polysaccharide Extracted From Longan (Dimocarpus Longan Lour.)

Longan (Dimocarpus longan lour), a native product of China, belongs to Sapindaceae of Dimocarpus Lour, which is one of the four precious fruit (Lichi, Banana and Pineapple) in the southern part of China. It has been regarded as the precious medicine and food in ancient times, according to ancient books which recorded longan has the function of nourishing blood, appetiting, moistering lung for arresting cough and healing postpartum edema and diarrehea. However, the shielf life is short because of running dry, brown stain and decaying fast caused by microorganism, and quantity of longan is offered as fresh stuff rather than processing products which account to less than30%. Moreover, the sharp increase of yielding and the restriction of storage, transporting and shrinked market, the promotion of economic benefit was restricted. It is necessary to improve the bioavailability of longan on the these basic aspects, such as researching effective components, the links between active compound and its structure, the mechanism of biology and pharmacology of active ingredients in order to carry out a scientic way to explore high quality products of longan medicinal and health care.Recently, much attention has been focused on the research of functional ingredients of longan fruit. Polysaccharide, a kind of physiological activator extracted from longan, has been proved to be functional stuff of anti-oxidation, immunoregulation and improving memory and physiological function of anti-tumor, anti-tyrosinase and inhibiting the reaction of glycosylation. Therefore, longan polysaccharide has become one of the subjects of studying in functional regredients. It has separated and purified polysaccharide extracted from longan, determined its molecular weight mass, analyzed structure, studied rheological properties and the effect of scavenning radicals in this work via the theory of food science, chemistry of natural product, and food chemistry and modern research techniques of analytical chemistry and instrumental analysis. The main research contents and conclusion were summarized.1. The method of determination of polysaccharide in longan was studied. After analyzing the accuracy, recovery and reproducibility of the three methods, the results showed that repeatability and precision of improved phenol-sulfuric acid method are better, and the relative standard deviation (RSD) is3.16%and0.88%, respectively. It also showed that the recoveries of three methods with no significance difference, the recover rate are101.24%,102.93%and103.85%, respectively.2. Polysaccharide was extacted from dried longan pulp (12.94%for wet basis moisture content) by hot water for2hours and three times with the condition of90℃for temperature and material/water at the rate of1:2. After deproteinization by Sevag and decoloration using hydrogen peroxide, crude longanpolysaccharide (CLP) became faint yellow and completely water-soluable polysaccharide (LP). According to experiment, it could extract7.44g LP from2.5Kg dried longan pulp. Then, LP has been purified on DEAE-cellulose52column chromatography. The yield of LPA, LPB, and LPC eluted from LP were8.35%,62.36%, and11.36%, respectively. LPB-2-M eluted from LP on Sephacryl S-400HR was identified to be pure polysaccharide. The average molecular weight of LPB-2-M were determined by HPGPC was8.0×104g· moL-1, and the diatribution ranges from2.7×104g·moL-1to4.1×105g·moL-1, besides, the molecular weight less than8.4×104g· moL-1account to90%more or less, and polydisperity was1.03.3. The physical and chemical properties were studied and the result showed that CLP was brown and partial water-soluable, LP was faint yellow, fluffy, and completely watersoluable, LPB-2-M was colorless powder and completely water-soluable. CLP, different from LP and LPB-2-M, consist of a bit of protein proved by ninhydrin reaction. They all contain uronic acid proved by carbozole-sulfuric acid and free of starch illustrated by I-KI reaction. TGA analysis present that LPB-2-M exist two distinct weight-loss processes, the first weight loss peak appeared at70℃, the rate of weight loss was10.85%; the first weight loss peak appeared at226.7℃-276.5℃, the rate of weight loss was38.77%, total weight-loss was49.62%. TGA analysis present that longan polysaccharide had a good heat-stability, which was not easy for thermal decomposition under230℃.4. It preliminarily studied rheological properties of longan polysaccharide and the effect of factors such as concentrate, pH, sucrose, Na+, and Ca2+by steady shear tests and small amplitude oscillatory tests. The result showed that longan polysaccharide present a pseudoplastic flow behavior which was evidented by shear shinning phenonmenon, it exist a solid-like behavior when its concentrate was more than3%, it was sensitive to pH condition and the viscosity descended greatly and irriversily under alkaline condition, the factors of sucrose, Na+, and Ca2+were done benefit to viscosity and viscoelastic properties which were dependency on concentrate, the type of flow behavior was not changed by the factors of sucrose, Na+, and Ca2+. It also indicated that polysaccharide was disaccord to Cox-Mrez empirical correlation.5. The structure of LPB-2-M was analyzed by UV-Vis, HPLC, IR, NMR and periodate oxidation reaction. The sugar content of CLP, LP, and LPB-2-M were35.26%,47.42%and84.32%, respectively, determined by phenol-sulfuric acid method, the uronic aicd content of CLP, LP, and LPB-2-M were0.17%,6.27%and7.61%, respectively, determined by carbazole-sulfuric acid method, while LP and LPB-2-M were barely in proteins. The monosaccharide compositions of LPB-2-M were ribose, rhamnose, fructose, glucose, arobinose, galactose and xylose, anomeric carbon contained more β-type than a-type, the bond types in LPB-2-M consist of1â†'6, and probable some1â†'2and1â†'4. This indicated LPB-2-M was an acidic heterosaccharide with branches.6. The activity of scavenging radicals by longan polysaccharide were investigated by the experiment of scavenging DPPH·, ABTs+, and HO·. It indicated longan polysaccharide present a higher activity in scavenging ABTs+than scavenging DPPH·, and the activity of scavenging HO· was weaker of them.