| With the improvement of living standards,diabetes has become a chronic disease which seriously endangers human health,among which,more than 90% of the patients with type 2 diabetes mellitus.Plants with dual purposes of medicine and food have the advantages of high safety and outstanding biological activity.Therefore,it is of great social and economic benefits to find out the functional factors with hypoglycemic effect from medicine and food dual purposes plants for improving type 2 diabetes mellitus.Moringa oleifera leaf is rich in a variety of bioactive substances.It is a trend to develop functional foods which can promote health by using Moringa oleifera leaf or its extracts as the raw materials.The active components of Moringa oleifera leaf were extracted by 16 kinds of methods and the effects of different extraction methods on the components and antioxidant activities of the extracts were investigated.Type 2 diabetic rats induced by High-fat-diet with streptozotocin(HFD+STZ)were used as model animals to study the hypoglycemic effect of enzymatic extract of Moringa oleifera leaf and its polysaccharide and small molecular components separated by ultrafiltration.The structure of Moringa oleifera leaf polysaccharide was analyzed to provide theoretical and methodological guidance for the development of healthy food with auxiliary hypoglycemic function and the intensive processing of Moringa oleifera leaf.(1)16 different extraction methods,including water/ethanol extraction(hot-water,55°C water,ultrasonic assisted water,ultrasonic assisted ethanol),enzymatic extraction(pancreatic enzyme,papain,Ns37071 protease,compound protease),enzymatic coupled ethanol extraction and enzymatic residue ultrasound assisted ethanol extraction,were used to prepare Moringa oleifera leaf extract.The effects of different extraction methods on the content of proteins,saccharides,phenolics and antioxidant activitives were investigated in order to extract the antioxidant components from the Moringa oleifera leaf purposefully.The results showed that the Moringa oleifera leaf extract possessing high proteins,saccharides and phenolics contents and strong antioxidant activity was obtained in terms of enzymatic extraction and enzymatic hydrolysis coupled with ethanol extraction.Ns37071 protease and pancreatin facilitated the extraction of proteins,saccharides,phenolics and antioxidants.The contribution rates of proteins(protein hydrolysates)and saccharides to the antioxidant activity of Moringa oleifera leaf extract were superior to those of phenolics,indicating that proteins(protein hydrolysates)and saccharides played important roles on the antioxidant activity of Moringa oleifera leaf extract.(2)Moringa oleifera leaf extraction(MLE),which is rich in phenolics,peptides and saccharides,was prepared by enzymatic hydrolysis of pancreatic.MLE was separated by 10 kDa ultrafiltration membrane to prepare polysaccharide component and small molecular component.Type 2 diabetic rats induced by HFD+STZ were used as model animals to study the hypoglycemic effect of MLE and its components and the possible hypoglycemic mechanism of MLE and its components with strong hypoglycemic activity will be further discussed.The results showed that MLE and its components can reduce fasting blood glucose and oral glucose tolerance and can improve insulin resistance in type 2 diabetic rats.Their hypoglycemic effects were as follows: MLE polysaccharide component > MLE small molecular component > MLE.MLE polysaccharide component is an important hypoglycemic functional factor in MLE,and its hypoglycemic activity is comparable to that of metformin.MLE polysaccharide component can effectively control type 2 diabetes by improving glucose tolerance and hyperinsulinemia,reducing insulin resistance,promoting liver glycogen synthesis and inhibiting it decomposition,antagonistic oxidative stress,regulating lipid metabolism and protecting and repairing islet tissue.(3)MLE polysaccharide component was fractionated by ethanol precipitation,deproteinization,decolorization and DEAE-Sepharose fast flow chromatogram to obtain 4 acidic polysaccharides(MLP-1,MLP-2,MLP-3 and MLP-4).The structures were analyzed by infrared spectroscopy(IR),1-phenyl-3-methyl-5-pyrazolone(PMP)precolumn derivatization-high performance liquid chromatography(HPLC),high performance gel permeation chromatography(HPLC),scanning electron microscopy(SEM)and methylation-gas chromatography mass spectrometry(GC-MS).The results showed that the four acidic polysaccharides in Moringa oleifera leaf were all composed of mannose,rhamnose,glucuronic acid,galacturonic acid,glucose,galactose and arabinose.Among them,MLP-1 is a kind of heteropolysaccharide with low molecular weight,low viscosity,flat and smooth surface,which is composed of main chain→3)Galp(1→,→5)Araf(1→and→3,6)Galp(1 → with high content and compact grid structure.MLP-2 is a kind of heteropolysaccharide with high molecular weight,low viscosity,porous network on the surface,and the main chain is formed by →3)Galp(1→,→5)Araf(1→ with high content and the structure of double main chain grid.MLP-3 is a kind of heteropolysaccharide with high molecular weight,low viscosity,irregular granule and convex flake on the surface,which is composed of main chain by →3)Galp(1→,and →3)Araf(1→ with high content and "branched" structure.MLP-4 is a kind of heteropolysaccharide with high molecular weight,low viscosity and irregular granular surface,and composed of main chain by →3)Galp(1→,→3)Rhap(1→ with high content.Moringa oleifera leaf prepared by enzymatic method has the characteristics of low viscosity,antioxidant,hypoglycemic and antihyperlipidemic activities,and can be used as a functional factor to assist the development of hypoglycemic healthy food. |
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