| Dioscoreae opposita Thunb.is a dry rhizome of perennial twining herbaceous vine of Dioscoreae family,which has high medicinal and edible values.Dioscorea opposita has a history of more than 2000 years in China.Because of its unique geographical environment and efficacy,it has become one of the "four famous huai medicine",and the tiegun-yams is one of the best variety of Dioscorea opposita.The peel of Dioscorea opposita is also a part of the treasure house of Dioscorea opposita resources,and the content of some components in the peel of Dioscorea opposita is even higher than that in the non peel part.Therefore,it is of great significance to study the physicochemical properties and biological activities of polysaccharides in the peel of Dioscorea opposite for the development and utilization of resources.The chelating modification of polysaccharide molecules may improve the activities of metal chelates,or generate new biological activity,so as to improve the utilization rate of metal chelates.It was found that the rust spots on Dioscorea opposita belonged to anthocyanins.Anthocyanins belong to flavonoid compounds,which are natural pigments with good water solubility and widely exist in various colorful plants.Natural anthocyanins have many functions,such as anti-oxidation,anti-cancer,antiinflammatory,protecting liver and vision improvement properties.Because the unstable structure of anthocyanins,they are easily affected by the temperature,p H and other factors.In this paper,the peel of Dioscorea opposita Thunb was used as the main research object.Hot water,hot-compressed water,acid and enzyme-assisted were applied to extract polysaccharides(DTTP-W,DTTP-HCW,DTTP-HA and DTTP-EAE)from the peel of Dioscorea opposita Thunb.The physicochemical properties,antioxidant and hypoglycemic activities of polysaccharides were analyzed.The polysaccharide molecules obtained by acid extraction were modified with different metal chelates,and the physicochemical properties and antioxidant activities of the modified polysaccharide metal chelates were evaluated.The main components were identified and the stability of anthocyanins was analyzed.The main results are as follows:(1)The influences of four extraction methods,including hot water,hot-compressed water,acid and enzyme-assisted were applied to extract polysaccharides(DTTP-W,DTTP-HCW,DTTP-HA and DTTP-EAE),on the yields,physicochemical properties,hypoglycemic and antioxidant activities of polysaccharides from DTTP were studied and compared.Among the four samples of polysaccharide,DTTP-HCW had the highest yield(19.55%).DTTP-HA produced the highest total carbohydrate content(85.08%)and uronic acid(13.2%).The results of monosaccharide analysis showed that the four polysaccharides had the same types of monosaccharide,but the molar percentage of monosaccharide compositions was different.Scanning electron microscopy(SEM)result indicated that the surface structures of the four samples of polysaccharide were different.The DTTP-HA exhibited irregular structure with many holes.Thermal analysis results indicated that DTTP-HA had the highest thermal stability among the four samples of polysaccharide.Triple helix structure analysis results revealed that DTTP-HA possessed a triple-helix structure.Among the four extracted methods,the DTTP-HA and DTTP-W exhibited higher hypoglycemic and antioxidant activities.The highest antioxidant activities and hypoglycemic activities of the DTTP-HA among the four samples of polysaccharide might be due to its high uronic acid content and low molecular weight.(2)Three kinds of metal chelates(iron chelate,zinc chelate and copper chelate),were obtained by the chelation reaction of polysaccharides with different metal ions.The results of FT-IR and UV showed that three kinds of metal chelate were successfully chelated with polysaccharide,and their metal contents were(9.47%),(4.02%)and(30.25%),respectively.The results of SEM showed that copper chelate and iron chelate were relatively concentrated,while zinc chelate was dispersed.The results of antioxidant activity showed that there were significant differences among the three chelates,and iron chelate has the best antioxidant effect.(3)The pigment of Dioscorea opposita Thunb.Was initial identified by UV.The results showed that the pigment belonged to anthocyanins.The components of anthocyanin were identified by UPLC-MS,which showed that there were 9 monomer components respectively Cyanidin-3,5-O-diglucoside,Cyanidin-3-O-galactoside,Cyanidin-3-O-glucoside,Cyanidin-3-O-sophoroside,cyanidin,Delphinidin,Peonidin-3,5-O-diglucoside,Peonidin,Petunidin.PH value has a great influence on the stability of anthocyanin.Under strong acid conditions(p H ≤ 3),the color of anthocyanin in the peel tended to red and stable.With the increase of p H value,the color gradually turned green and the stability became worse.High temperature also had a certain effect on the stability of anthocyanin.The higher the temperature,the faster the degradation of anthocyanin.and the more stable and easier to store the anthocyanins in the lower temperature environment.The effects of Fe2+ and Fe3+ have relatively greater influence on the stability of anthocyanin in the peel of Dioscorea opposita Thunb.,while Cu2+,Ca2+,Zn2+ and Mn2+ have no significant influence on the stability of anthocyanin. |
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