Study On The Structure And Physicochemical Properties Of Two Kinds Of Cynanchum Auriculatum Royle Ex Wight Starch

Cynanchum auriculatum Royle ex Wight（also called‘Baishouwu’in Chinese）can be used as traditional Chinese medicine.Up to now,the researches about C.auriculatum mainly focused on the chemical components and its pharmacological effects.Many studies showed the properties of starch are closely related to the processing properties and uses of starch.However,the dry root of C.auriculatum contains about 50%of starch.In order to widen the precise applications of C.auriculatum in food industry,it is essential to investigate structural characterizations and physicochemical properties of starch.In this thesis,the morphological characteristics,crystal structure,short-range ordered structure,fine structure of amylopectin,thermodynamic properties,gelatinization properties,solubility,swelling power,and retrogradation properties of two kinds of C.auriculatum starch were studied.The main results are as follows:1.The protein,fat,ash,moisture,phosphorus,amylose,and total starch of YW201501 starch were 0.29%,0.96%,0.55%,7.33%,0.017%,21.81%,and 91.31%,respectively.The protein,fat,ash,moisture,phosphorus,amylose,and total starch of BW201001 starch were 0.37%,0.64%,0.46%,7.63%,0.022%,18.81%,and 90.05%,respectively.2.The starch granules were smooth,without cracks,and were irregular with spherical or polygonal shape.The polarized cross results showed that Maltese cross was located in the center of the granules.Both starches showed the characteristic B type X-ray pattern.The crystallinity of YW201501 starch and BW201001 starch was 21.50%and 20.48%,respectively.FTIR results showed that the short-range order degree was0.74 and 0.68,respectively.There were phosphate groups in both starch samples.3.The weight-average molecular weights of YW201501 starch and BW201001starch were 4.27×10⁷ g/mol and 3.58×10⁷ g/mol,respectively.The Rz values of YW201501 starch and BW201001 starch were 125.60 nm and 186.60 nm,respectively.The proportions of A chain,B₁ chain,B₂ chain,and B₃ chain of YW201501 starch were29.79%,49.72%,12.49%,and 8.01%,respectively.The proportions of A chain,B₁chain,B₂ chain,and B₃ chain of BW201001 starch were 28.14%,50.29%,13.59%,and7.97%,respectively.The average degree of polymerization of YW201501 and BW201001was 18.77%and 19.11%,respectively.4.Both starches were pseudoplastic fluids and weak elastic gels.The swelling force,viscosity,freeze-thaw stability,hardness,cohesiveness and digestion rate of YW201501 starch were higher than those of BW201001 starch,but its gelatinization temperature,transparency and resistant starch content were lower than those of BW201001 starch.The results of retrogradation properties showed that as the retrogradation time increased,the distances of interchain hydrogen bonds and inter-double helix hydrogen bonds decreased.At the same time,hydrogen bond energy,short-range order,and retragradation degree increased.The results of low-field NMR showed that as the retragradation degree increased,accompanied by an increased in free water content and a decreased in internal water content.In conclusion,the apparent morphology of the two starches was similar.Both starches were B-type crystals,containing phosphate groups and had a high content of resistant starch.Compared to BW201001 starch,YW201501 starch had a higher viscosity,retrogradation degree,swelling power,Mw,and proportion of A chains.While the transparency,synernsis,solubility,average chain length,and proportion of B1 chains were lower than BW201001 starch.The above results can provide a theoretical guidence for the precise applications of Baishouwu starch in food industry.