Research On Extraction, Purification And Hypolipidemic Mechanism Of Sweet-potato Water-soluble Glycoprotein

Sweet potatoe which originated from South Africa belongs to the morning-glory family and ranks as the world's seventh most important food crop. More than 117 million tons are produced in China annually—accounts for 90 percent of worldwide production. Sweet potato was used as raw material in this dissertation, and sweet potato water-soluble glycoprotein (SPG) was isolated and purified. Physical and chemical properties, composition, structure, and mechanism of hypolipidemic were systematic studied in order to make better use of sweet potato in order to develop new hypolipidemic health food.In this paper, SPG was extracted from sweet potato by water. The single factor and orthogonal experiment were used to determine the best extracting conditions; studied DEAE-cellulose 52 chromatography for the purification of sweet potato glycoprotein conditions; then using Sephacryl S-300 of the sweet potato glycoprotein further purification. By SDS-polyacrylamide gel electrophoresis of sweet potato glycoprotein for purity; studied the sweet potato glycoprotein of physical and chemical properties; the composition of sugar and amino acids of SPG were analyzed. Sweet potato glycoprotein thermodynamic properties was studied by DSC; using nuclear magnetic resonance, infrared spectroscopy, UV and mass spectrometry for the Sweet Potato structural glycoprotein analysis. Through animal experiments, research on sweet potato glycoprotein hyperlipidemia rats' blood lipid levels and explore the mechanism of hypolipidemic and a variety of factors on the processing of hypolipidemic effect of sweet potato. The main conclusions of the study are as follows:1. The best extraction conditions of sweet potato water-soluble glycoprotein were chosen by the single-factor test: grinding degree is 40 mesh, the ratio of raw material to water is 1:15, extraction time is 1h, extraction times is 3, at room temperature.2. The 0.00, 0.05, 0.10, 0.50 mol / L solution of sodium bicarbonate as DEAE-52 cellulose ion-exchange chromatography stage eluting agent is better. Sweet Potato glycoprotein purification purified by using DEAE-52 cellulose chromatography for the first step, then purified by Sephacryl S-300 gel chromatography. 3. Sweet potato water-soluble Glycoprotein freeze-dried products is white solid flocculation. Soluble in water and the solution is yellow, insoluble in high concentrations of ethanol, acetone, and other organic solvents. Under the concentration of SPG is 1.02g/mL, pH = 5.6, glutinosity is 2.95mPa.s, degree of opticity is [α]_D^25℃=+46o (C=0.29,H₂O), UV absorption is 280nm. Sweet potato glycoprotein samples of the protein content of 71.65 percent, reducing sugar content of 27.41 percent.4. Sweet potato water-soluble glycoprotein almost contains a variety of amino acids, aspartic acid, glutamic acid, arginine, cysteine, phenylalanine, leucine with a high level. Sweet potato water-soluble glycoprotein with 8 kinds of essential amino acids and the content is close to the WHO recommended which shows sweet potato water-soluble glycoprotein is a high-quality plant protein. The single type of sugar in sweet-potato Glycoprotein sample is rhamnose, arabinose, xylose, mannose, glucose and galactose.5. Sweet potato water-soluble glycoprotein thermal denaturizing temperature is 45°C, and after the deglycosylated , the thermal denaturizing temperature is 38.5℃, therefore glycoprotein oligosaccharides on the protein molecules has better stability which enhanced anti-denatured function.6. With the treatment of NaOH , Sweet potato Glycoprotein was significant absorpt at 240nm which shows that glycopeptide linkage existed in SPG.7. Sweet potato Glycoprotein can effectively reduce hyperlipidemia rats blood lipid levels and improve lipid metabolism and reduce atherosclerosis risk. The main features as follows: oral administration of different doses of the sweet potato glycoprotein, hyperlipidemia rats TG, TC, LDL-C decreased significantly, HDL-C increased significantly, the atherogenic index decreased significantly and shows dose-response relationship. The result shows that the sweet potato glycoprotein can improve hyperlipidemia rats' lipid metabolism, which prevent the occurrence of atherosclerosis.8. Sweet potato Glycoprotein hypolipidemic mechanism are: increase the level of HDL-C and Apolipoprotein Aâ… (ApoAâ… ), activate LCAT, identify HDL receptor which promote the lipid rotation and excretion; inhibit cholesterol synthesis key rate-limiting enzyme HMG-coenzyme A reductase (HMG-C_oA reductase), which block the liver cells of endogenous synthesis of cholesterol; raise lecithin cholesterol acyltransferase (LCAT) activity which promote Esterification of cholesterol, to increase cells free cholesterol esterification into cholesterol ester, speed up the cholesterol decomposition in the body.Sweet potato water-soluble glycoprotein increased activity of LCAT which reason may be that promote the liver manufacturing more LCAT molecular; or increase the level of HDL-C and Apolipoprotein Aâ… (ApoAâ… ), activate LCAT.Sweet potato glycoprotein may be adopted with the HMG coenzyme A reductase (HMG-C_oA reductase), has Strong competitive inhibition on HMG coenzyme A reductase (HMG-C_oA reductase) which increase LDL-C receptor expression, strengthen the cleaning of plasma ApoB and LDL, and reduce the formation of cholesterol.9. The temperature has a greater impact on sweet potato water-soluble glycoprotein activity. During sweet potato processing should avoid the high temperature above 60°C. Sweet potato water-soluble glycoprotein is steady when pH is 3～6. UV-treated to the sweet water-soluble glycoprotein almost no significant effect on hypolipidemic compared with the former.