Extraction And Structural Characteristic Of Polysaccharides From Arctium Lappa Linn.,radix

Arctium lappa L.（Burdock）,popularly known as“Dalizi”or“Bianfuci”,has spread throughout Eurasia and North America.It is used as both medicine and food throughout history,which is of highly nutritive value.Previous studies focused on biological active substances existing in the seeds of burdock,while burdock roots have been sadly neglected.In fact,as a vegetable in Shandong,Heilongjiang,Jiangsu and Taiwan provinces,burdock roots are rich in polysaccharides,proteins,calcium,phosphorus,iron and other nutriment.Currently,with the exploration of the nutrition of burdock roots,the function of burdock roots receives more and more attention.Obviously,burdock tea sales are increasing year by year.In this thesis,the research on chemical composition of burdock roots,isolation and purification of burdock root polysaccharides,and the structure and rheological properties were conducted.The purpose of the study is to provide guidance for the development of new specialty foods and comprehensive utilization of burdock roots.Main contents and results are summarized as follows:1.This experiment determined the contents of protein,fat,fructan and other chemical compositions of burdock roots according to relevant national or international standards.100 g burdock root thin slice contains 5.28 g water,4.8 g ash,4.92 g crude fiber,42.41 g fructan,3.05 g fat,12.30 g protein,22.73 g starch,224.63mg sodium,974.88 mg kalium,364.90 mg calcium,394.14 mg magnesium,30.96mg iron,3.13 mg cuprum and 2.25 mg zinc.Among the heavy metal,chromium was detected and its content was 0.09μg/100 g,while cadmium and plumbum was not detected.2.The crude polysaccharide from dry powder of burdock roots was extracted by hot water.During the extracting process,the effects of three main factors including water to solid ratio,extraction temperature and extraction time on the yield of crude polysaccharide from burdock roots were studied using single factor analysis method.Optimum conditions for the extraction of polysaccharide were studied by the response surface method based on a Box-Behnken experiment design in three factors and three levels.The optimized extraction condition was determined to be at water to solid ratio of 11.81 mL/g,temperature 83.96^°C,and time 88.12min,thus the relevant yield was 87.53 g/100g.3.Water extracted polysaccharide from burdock roots WPB was isolated by repeatedly ethanol precipitation.The structure of WPB was studied by infrared spectroscopy,ion exchange chromatography,nuclear magnetic resonance spectrum and other analytical methods.The results indicated that 100 g WPB contains 3.12 g water,1.76 g ash,91.31 g total sugar,84.58 g fructan,73.85 mg sodium,484.12 mg kalium,158.25 mg calcium and 239.89 mg magnesium.Among the heavy metal,chromium was detected whose content was 0.08μg/100 g,while cadmium and plumbum was not detected.WPB was composed of fructose（88.9%）and glucose（1.2%）.The relative weight-average molecular weight（M_w）of WPB was 2404 Da.Two strong absorption peaks at 1100¹010 cm^-11 and the peaks at 934 cm^-1,874 cm^-1and 821 cm^-11 indicated that WPB was composed of furanose.According to ¹H NMR and ¹³ C NMR results,WPB was elucidated to be a inulin,consisting of→2)-β-Fruf-(1→,β-Fruf-(2→andα-Glcp-(1→.4.The residue of water extraction was further extracted by 0.25%（w/v）of ammonium oxalate solution to get AOE.After fractional precipitation by ethanol,AOE-20,AOE-40,AOE-60 and AOE-80 were separated from each other.AOE was composed chiefly of fructose（71.7%）and galacturonic acid（12.3%）.It also contained a small quantity of arabinose,glucose,galactose and rhamnose.Scanning electron microscopic photographs of AOE at different magnifications indicated the rod-like,irregular spherical and flaky structures.A slight mass loss in AOE（¹0%）occurred at around 100°C due to the evaporation of moisture.The major degradation of AOE began at around 217^°C.The greatest mass losses of AOE（62%）appeared in the temperature range of 217³50^°C.AOE-20&AOE-40 were comprised mainly of galacturonic acid,while they did not contain fructose.AOE-60&AOE-80 were some kind of fructan which were composed chiefly of fructose.The weight average molecular weights were 4.84×10⁵,4.09×10⁵,3.71×10⁵ and 5.21×10³Da for AOE-20,AOE-40,AOE-60 and AOE-80,successively.Intrinsic viscosity of AOE-20 was 112.42 mL/g,while it was 113.69（AOE-40）,96.22（AOE-60）and 6.78（AOE-80）mL/g.5.The rheological property of AOE was studied.At concentrations lower than0.75%（w/v）,the apparent viscosity of AOE was almost independent on the shear rate.When the concentrations increased to 1.0%³.0%（w/v）,no Newtonian plateaus were observed at lowγ,but obvious shear-thinning behaviors occurred.What’s more,the degree of shear-thinning and the viscosities exhibited concentration dependence,which was the typical feature of pseudoplastic fluids.AOE performed typical weak gel-like behavior as G′was larger than G″over the entire experimental frequency range,and the two moduli approached each other with the frequency increased.The values of G′and G″increased with the increase of frequency and no cross-over point was found.Gellan was mingled with AOE.When ratio of AOE to gellan ratio was kept at 7:3,the blending had maximum value of the storage modulus and gelation ability.