Effects Of Decolorization On The Structure And Physicochemical Properties Of Polysaccharides From Thesium Chinense Turcz.

Decolorization is an important step in the process of refining polysaccharides.In this test,the polysaccharides from Thesium chinense Turcz.（T.chinense）were used as the research object.The two methods of oxidative decolorization（hydrogen peroxide）and adsorption decolorization（activated carbon）were used to decolorize.In order to explore the effects of different decolorization methods on the structure and physicochemical properties of T.chinense polysaccharides,hydrogen peroxide polysaccharide samples（HTP）and activated carbon polysaccharide samples（CTP）were compared in terms of structure,antioxidant activity and complex gel properties.The main findings are as follows:1 Optimization of decolorization process.A single factor experiment was used to analyze the influence of the amount of activated carbon,p H,temperature and time on the decolorization effect,and then orthogonal experiments were used to optimize the decolorization conditions.The best combination of decolorization conditions was activated carbon addition 0.5%,p H 5.0,the temperature 40°C and time 60 min.At this time,the polysaccharide retention rate and the pigment clearance rate were 85.16%and 79.48%,respectively.For the decolorization method of hydrogen peroxide,we referred to the literature previously published by the research group.2 Analysis of basic components and apparent characteristics of HTP and CTP.First,HTP and CTP were compared,including total sugar content and soluble protein content.Secondly,the solubility and rheological properties of HTP and CTP were compared.The results showed that there was no significant difference in total sugar content（HTP:45.19%±2.26,CTP:42.63%±1.36）and soluble protein content（HTP:0.48%±0.03,CTP:0.77%±0.09）.HTP and CTP have different solubility in water（HTP:75.33%±0.12,CTP:99.70%±0.15）.The apparent viscosity of the two polysaccharide samples increased with the increase of polysaccharide content,and showed obvious characteristics of non-Newtonian fluid in the shear rate range of 0.01-100 1/S.In addition,when the sample solution concentration was the same,CTP has a higher viscosity than HTP.3 Characterization of HTP and CTP structures.The different decolorization mechanisms of hydrogen peroxide and activated carbon may affect the structure of the polysaccharides of T.chinense.Therefore,the functional group content,monosaccharide composition,molecular weight,infrared spectrum,X-ray diffraction（XRD）spectrum,atomic force microscope（AFM）spectrum and thermogravimetric（TG）spectrum of HTP and CTP were analyzed in this experiment.The results showed that the sulfuric acid group contents of HTP and CTP were 7.03%±0.03 and 14.33%±0.04,and the uronic acid contents were 35.02%±0.03 and 14.01%±0.01,respectively,with significant differences（p<0.01）.Both HTP and CTP were composed of mannose,rhamnose,glucuronic acid,galacturonic acid,glucose,galactose,and arabinose,but the composition ratios were different（HTP:3.24:5.01:1.31:24.33:16.84:23.53:25.64,CTP:0.78:4.21:3.10:0.82:30.66:37.25:23.18）.CTP had a larger molecular weight（HTP:8.349×10⁴g/mol;CTP:3.064×10⁵g/mol）.FT-IR spectroscopy indicated that both samples were in accordance with the typical characteristics of polysaccharide samples,but the HTP-COOH vibration absorption peak was obvious,while the CTP-S=O absorption peak was obvious.XRD pattern results showed that CTP has a more obvious crystal structure.AFM results showed that the molecular morphology of HTP and CTP were spherical,and the CTP structure was larger.The TG curve showed that the thermal stability of the CTP sample was poor,but the HTP sample contained more volatile components（weight loss rate:HTP 59.33%,CTP53.21%）.Therefore,the structure of polysaccharides prepared by different decolorization methods was different.4 Analysis of antioxidant activity of HTP and CTP.The antioxidative activities of HTP and CTP were determined by using chemical model and cell model respectively.The results were as follows:in the chemical model antioxidant experiment,the semi-inhibitory concentration(IC₅₀)of HTP and CTP to three free radicals（DPPH^-,ABTS⁺and OH^-）were4.4,2.0,3.1 mg/m L;4.0,2.2,3.8 mg/m L.In the cell model antioxidant experiment,HTP and CTP had the strongest antioxidant effect at a concentration of 2 mg/m L（74.06%,60.36%）.In general,HTP had better antioxidant capacity than CTP.5 Effects of HTP and CTP on the gelation properties ofκ-carrageenan.The viscosity of HTP and CTP were relatively small.They did not show good gel properties.However,appropriate concentrations of HTP and CTP were added toκ-carrageenan to improve gel performance.The improvement was most obvious when the mass ratio of added polysaccharide toκ-carrageenan was 0.2:1.8（wt%）.The gel temperature was increased from 47.9°C to 50.4°C（HTP）and 49.3°C（CTP）,the sol temperature was increased from64.3°C to 70.9°C（HTP）and 71.3°C（CTP）.