Physicochemical,structural Antioxidant Activities Of Bulbil Starch And Polysaccharides From Dioscorea Opposita Thunb.by-products

Huaishan-yams(Dioscoreae opposita Thunb.)is a perennial winding herbaceous vine of the Dioscoreaceae family.It is one of the four Huaiqing chinese medicines.Its endophytic fungi and bulbil are also part of the treasure house of huaishan-yams resources.It is interesting to obtain polysaccharide and starch from D.opposita Thunb.to analyze and characterize its structures,which can be used as a potential antioxidant,and can provide theoretical basis for the future use in related fields.In this paper,bulbil starch of and endophytic fungi polysaccharide of D.opposita Thunb.were mainly studied.First,the current work has evaluated effects of different isolation methods(aqueous steeping,alkaline steeping and enzyme steeping)on the physicochemical,functional,and structural properties of bulbils starch of D.opposita Thunb.Second,the structure characterization of purified polysaccharide fragments from bulbil residues and their antioxidant activities were evaluated.Third,studing the accumulation and antioxidant activity of secondary metabolites of 23 purified endophytic fungi from D.opposita Thunb.and screen the strains with high contents of secondary metabolites and good antioxidant activities.Finally,the structure characterization of purified polysaccharide fragments from the fruiting bodies of Alternaria alternata and their antioxidant activities were evaluated.The main findings are as follows:(1)Starch isolated from bulbils of D.opposita Thunb.by the aqueous steeping extraction(SBS)method afforded higher extraction yield and lower starch content as compared with enzyme(EBS)and alkaline(ABS)extraction methods.The starch granules were oval,spherical and kidney-shaped and the surface of the ABS and SBS granules appeared to be slightly rough.The starches having larger average granule size showed more amylose and phosphorus contents than those with smaller average granule size.Differential scanning calorimetry(DSC)exhibited that the SBS had an endothermic transition ranging from 65.8℃ to 76.3℃ with enthalpy of 2.0 J/g.The endothermic transitions of ABS and EBS showed the regions of 67.9 ℃ to 73.0℃,and 66.8℃ to 82.0℃,respectively.The gelationization enthalpies of ABS and EBS were 13.8 and 11.5 J/g,respectively.Additionally,ABS presented greater clarity in comparison with EBS and SBS.Pasting properties indicated that ABS had the highest peak viscosity,breakdown,but SBS had the lowest trough,final viscosity,setback,and pasting temperature.Generally,extracting starch from this bulbil and identification were crucial to the future application of these starches in the food and nonfood areas.(2)Purification DEAE-52 cellulose column chromatography and structural characterization of D.opposite Thunb.bulbil residues polysaccharides were investigated and its antioxidant activities were analyzed.Results indicated that two component purified polysaccharides with molecular weight(Mw)of 21.9 and 109.79 KDa were obtained,named as DBP1 and DBP2.DBP1 was the neutral polysaccharides,while DBP2 was the acidic polysaccharides.The monosaccharide composition analysis showed that the 9 monosaccharides were determined from DBP1,while 11 monosaccharides were determined from DBP2.The results from TGA and DSC showed that DBP1 and DBP2 may structurally be stable and have good thermal stability under 205,252 ℃,respectively.The methylation and GC-MS analysis showed that DBP1 is mainly composed of a Galp backbone linked 1→4 and with some 1,3-Glcp,1,6-Glcp and 1,6-Galp bonds which could be in the backbone or the side chains.The determination of the antioxidant activities showed that DBP1 and DBP2 having good DPPH radical scavenging activity and DBP2 having good hydroxyl radical scavenging activity in the test.These numbers indicated that the polysaccharides from Dioscorea opposita Thunb.bulbil residue is edible natural antioxidant.(3)Among the 23 endophytic fungi from D.opposita Thumb.,the contents of the dominant sugar producing strains were S3(A.alternata)and S4(Epicoccum nigrum),accounting for 2.81%and 2.83%of the dry mycelium weight,respectively.Furthermore,the contents of dominant sugar producing strain was L12(Trichoderma sp.)in fermentation broth with the contents of 2995.76 mg/L.All the extracts of these 3 strains above have the close DPPH radicals scavenging ability with 0.05 mg/mL vitamin C(Vc)and their hydroxyl radical scavenging abilities were significantly higher than those of Vc at 1.0 mg/mL.In this study,6 dominant fungi strains with high contents of secondary metabolites and good antioxidant activities were screened from mycelium and fermentation broth of Dioscorea opposita Thunb.,respectively.This experimental results will provide a reference for the further purification of secondary metabolites and discovery of the active ingredients from D.opposita Thunb.(4)The extraction,purification by DEAE-52 cellulose column and Sephadex G-100 column chromatography and structural of fruiting bodies of A.alternata polysaccharides and their antioxidant activities were investigated in this study.Two water-soluble neutral polysaccharides,designated as AltP1,AItP2,were purified and the carbohydrate contents were found to be 981.95 and 823.43 mg/g,respectively.The the molecular weight(Mw)of Altp1 and Altp2 are 20.34 KDa and 22.45 KDa,and the main components of monosaccharides are galactose,glucose and mannose.Their backbone is similar,and both contain a large number of 1,6-Manp.The results from TGA and DSC showed that Altpl and Altp2 may structurally be stable and have good thermal stability under 205℃,respectively.The antioxidant activity results showed that Altpl and Altp2 showed significant DPPH radical and ABTS+radical scavenging activity in the test concentration range.Among them,the maximum DPPH radical inhibition rate of Altpl and Altp2 reached 95.83%and 86.11%,which was almost the same as Vc.In addition,Altp1 and Altp2 showed a certain Fe3+reducing power in the test.The above results indicated that:(1)Different isolation methods induced changes in the morphology of starch granules and chemical composition,which led to distinct functional properties.In the practical application process,people could choose the proper bulbil starch obtained by different extraction methods according to different characteristics.(2)There are many of active polysaccharides in metabolites of some endophytic fungis from D.opposita Thunb.,which has development and research value.(3)The molecular weight,monosaccharide composition,types of glycosidic bonds,and different antioxidant activity indexes of the purified polysaccharide from bulbil residue and the mycelium of A.alternata mycelia are obviously different.It is different from the polysaccharides of the rhizomes of D.opposita Thunb.which have been studied.This indicates that the structure and activity of polysaccharide fragments in different parts are different.The difference in antioxidant activities are that the endophytic fungus intracellular polysaccharides of D.opposita Thunb.are the strongest,and the polysaccharides of D.opposita Thunb.bulbil residue is centered.These two parts of polysaccharides have great in-depth research and development value.