| Sargassum thunbergii is a unique warm temperate algae in the western North Pacific Ocean,grows in the coastal intertidal zone.Because the algae body is dark brown and looks like Rattail,so it also known as Rattail and Sea Pine.And it often used as a natural bait for aquatic animals such as sea cucumber and abalone.From the north of Liaodong peninsula to Leizhou peninsula,China has a large distribution of Sargassum thunbergii.At home and abroad,the research on Sargassum thunbergii is focused on the active mechanism and structure of small molecules,such as polyphenols and fucoxanthin.And there are few reports on polysaccharides.Therefore,in order to provide a theoretical basis for further research on Sargassum thunbergii,so as to better develop and make full utilization of Sargassum resources,this paper systematically studied the polysaccharides from Sargassum thunbergii,including its extraction and static rheological properties,separation and purification,physical and chemical properties and structure analysis,antioxidant and in vitro immune activity,the characteristics in vitro simulated digestive and fermentation,and the regulation of intestinal flora.1.Extraction and rheological properties of STPThe crude polysaccharide of Sargassum thunbergii was extracted by hot water,and the excess protein was removed by TC A.The effects of concentration,temperature,pH,NaCl and sucrose addition on the apparent viscosity of crude polysaccharides from Sargassum thunbergii were investigated.The results showed that the apparent viscosity increased with the increase of polysaccharide concentration.The apparent viscosity of polysaccharide solution is higher at lower temperature.The crude polysaccharides from Sargassum thunbergii were stable in acidic and weak alkaline solutions.Addition of NaCl and sucrose could increase the apparent viscosity of polysaccharide solution,and the addition of NaCl was positively correlated with the viscosity.2.Isolation,purification,physicochemical properties and structural analysis of STPThe crude polysaccharide of Sargassum thunbergii was separated and purified by DEAE-52 cellulose.Three purified components STP-1,STP-2 and STP-3 were obtained,and the main components were STP-2.HPGLC was used to determine the purity and relative molecular weight of STP-1,STP-2 and STP-3.The results showed that their purified components were relatively homogeneous,with molecular weights of 1006.93 KDa,831.76 KDa and 893.31 KDa,respectively.FT-IR was used to study the structure composition and characteristic absorption peaks of the polysaccharide from Sargassum thunbergii.The physicochemical properties of crude polysaccharide from Sargassum thunbergii and its pure products were determined by chemical methods,including the contents of total sugar,protein,glucuronic acid,sulfuric radical and polyphenol.The total sugar contents of STP,STP-1,STP-2 and STP-3 were 37.83%,51.70%,41.10%and 40.00%,protein content was 0.98%,0.92%,0.60%and 0.65%,glucuronic acid content was 22.26%,29.28%,41.68%and 30.16%,sulfuric radical was 8.26%,0.68%,4.23%and 5.86%,polyphenol content was 1.36,1.03,0.49 and 0.45 mg GAE/100mg,respectively.3.Antioxidant and immunomodulatory activity of STPThe antioxidant activities of crude polysaccharides from Sargassum thunbergii and their purified components were evaluated by chemical methods(scavenging DPPH free radicals,superoxide anion free radicals,ABTS free radicals and reducing power).The results showed that STP,STP-1,STP-2 and STP-3 had strong superoxide anion free radical scavenging activity,DPPH free radical scavenging activity and ABTS free radical scavenging activity,and had certain reducing power.The immune activity of STP-2 was studied by using RAW264.7 mouse macrophage as an in vitro immune model.STP-2 can promote the proliferation of RAW264.7 cells and the release of NO and cytokines TNF-α and IL-6,indicating that STP-2 has certain immunoregulatory activity.4.Simulated digestion of STP in vitro and its probiotic effect on intestinal floraIn this section,the digestive properties of STP in mouth,stomach and small intestine were studied by simulating digestive system in vitro.The experimental results showed that the relative molecular mass of STP in saliva,gastric juice and small intestinal juice did not change.At the same time,the content of reducing sugar in digestive juice did not change significantly before and after digestion,indicating that no free sugar was produced during the whole digestive process of digestive system.Therefore,STP will not be digested in the whole digestive system,so it can enter the large intestine smoothly.The effects of STP on intestinal microorganisms in vitro and the utilization of STP in intestinal microenvironment were studied by using in vitro anaerobic fermentation model and high throughput sequencing technology.After 24 hours of fermentation in the large intestine,the relative molecular weight of STP decreased significantly in the response value of HPLC,and the contents of total carbohydrates and reducing sugars in fermentation also decreased significantly,indicating that intestinal microorganisms could partially utilize STP.STP can also change the composition of intestinal microorganisms in normal group and IBD group.STP can significantly reduce the proportion of Firmicutes/Bacteroidetes and significantly increase the relative abundance of Bacteroides at the level of science.Meanwhile,compared with OR group,STP decreased the pH value of fermentation broth,and the content of short-chain fatty acids in normal group increased to 23.358±1.719 mM after 24 hours of fermentation.The content of short-chain fatty acids in IBD group increased to 13.157± 0.226 mM after 24 hours of fermentation.The content of acetic acid,lactic acid,propionic acid and n-butyric acid in normal group increased significantly,but only lactic acid and acetic acid in IBD group increased significantly.Therefore,STP can not only regulate the healthy intestinal microecology,but also regulate the intestinal microecology of IBD patients. |
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