| Gracilaria lemaneiformis is a medicinal and edible marine plant,which can be used as medicine and food.It contains many kinds of active biological macromolecules such as polysaccharide,dietary fiber and biological pigment,which is widely used in food,industry,medicine and cosmetics industry.A large number of studies have shown that polysaccharide and dietary fiber have the biological activities of immunomodulatory,hypoglycemic,hypolipidemic and so on.In this thesis,polysaccharides and dietary fibers of Gracilaria lemaneiformis were extracted and characterized,and their physicochemical properties and functional activities were studied.The results are as follows:1.The extraction process of Gracilaria lemaneiformis polysaccharide was optimized by accelerated solvent extraction,with the polysaccharide yield as the response value,the extraction temperature,extraction time and cycle number as independent variables,and the optimal extraction process conditions of the polysaccharide were obtained by single-factor test combined with Box-Benhnken response surface analysis: the pressure was 10 MPa,the extraction temperature was70 °C,the extraction time was 8.5 min,the number of cycles was 4 times,and the polysaccharide yield was 9.58 ± 0.31%.The differences in structure and physicochemical properties of the two polysaccharides were systematically compared.Fourier infrared spectroscopy showed that the polysaccharide functional group obtained by the two different preparation methods was not significant.The thermogravimetric results showed that the stability of polysaccharides from Gracilaria lemaneiformis by accelerated solvent extraction(GLP-K)was better than polysaccharides from Gracilaria lemaneiformis by hot water(GLP-W).The microscopic morphology of GLP-K was fragmented and loose,with an average molecular weight of 747.122 KDa.The composition analysis of monosaccharides showed that GLP-K was mainly composed of galactose,glucuronic acid and rhamnose,and its molar ratio was 36.2624:2.5354:1.5238;GLP-W showed an irregular fold morphology with holes;and the average molecular weight was 4.302 103 KDa.It is mainly composed of galactose,glucuronic acid and glucose,and its molar ratio is37.3124:4.805:3.4177;Congo red experiments show that GLP-K and GLP-W both have triple helix structure.2.The ash,water and protein contents of Gracilaria lemaneiformis were 20.80%,9.05% and 19.18%,and the total dietary fiber,soluble dietary fiber and insoluble dietary fiber content were 47.90%,11.80% and 36.1%.Dietary fiber was extracted by alkali method,microwave-assisted alkali method and microwave-assisted enzyme method.The three dietary fiber structures were characterized by infrared spectroscopy,thermogravimetric method,scanning electron microscope and high performance liquid chromatography.Compared with microwave-assisted enzyme method,alkali method and microwave-assisted alkali method reduced the molecular weight of soluble dietary fiber,made the microstructure more fine,and improved thermal stability,but infrared showed that there was no difference in functional group structure.3.Antioxidant experiments showed that GLP-K had high oxidation resistance,and the scavenging rate of DPPH radicals could reach 28.52%.and α-amylase inhibitory capacity was 54.04%;GLP-K has no significant cytotoxic effects at or below the concentrations of 1000 μmol/L,and the NO inhibition rate is 69.47% at 500 μg/mL.It has good antioxidant,hypoglycemic and anti-inflammatory activities in vitro.The physicochemical properties and biological activities of dietary fiber of Gracilaria lemaneiformis were studied.The results showed that compared with microwaveassisted enzymes,the water holding capacity,water bound capacity,water swelling capacity and oil holding capacity of IDF obtained by alkali and microwave-assisted alkali methods were significantly increased.The the water holding capacity,water bound capacity,water swelling capacity of SDF decreased significantly with alkali and microwave-assisted alkaline methods,but the oil holding capacity increased significantly.The cholesterol adsorption capacity,nitrite adsorption capacity,glucose adsorption capacity and α-amylase inhibition capacity of IDF extracted by alkali method were all greater than those obtained by microwave-assisted enzyme method and microwave-assisted alkali method. |
