Study On Extraction,Purification And Physicochemical Characteristics Of Coix Seed Starch

Coix Seed,belongs to the dry and ripe seeds of Coix lachryma-jobi L,is one of special economical crop of Fujian province,which has rich nutrition and Special medical care benefits.Currently,its research mainly focuses on the physiological and pharmacological functions of Coix Seed’s polysaccharide and lipid and the development of its’ product.But there are little literatures about coix seed starch that is main composition of coix seed.Therefore,in this paper,the special coix seed from Pucheng city was used as raw material,and the extraction,purification,physicochemical and structural characteristics of coix seed starch were investigated by polarized-light microscopy,scanning electron microscope,X-ray diffraction,gel permeation chromatography,differential scanning calorimetry,etc.These results will provide important theoretical basis and the guiding principle for the development of high-value utilization of coix seed starch.The main results are as follows:1、The single factor result of starch extracted from coix seed by lye extraction showed that the optimum condition of isolation of starch was extracting time 5h、solid to liquid ratio was 1:5、NaOH concentration 0.5%.The degree of regression fitting from response surface analysis was well.The optimum technology of isolation of starch from Computer software simulation was extracting time 5.11 h,solid to liquid ratio was 1:5.23,NaOH concentration 0.52%.According to this technology,the extraction ratio of coix seed starch from actual experimental operation is 71.08%,which is close to predictive value 71.5221%.It indicated that the validity of model.The raw starch was further purified by organic solvents and alkali protease,and the purity starch(97.54±0.61)%,residual quantity of protein(0.38 ± 0.05)%was obtained.The content of amylase of coix seed starch was(8.25 ± 0.76)%,which was a little higher than starch from general grain.2、The physicochemical and structural characteristics of coix seed starch were investigated by polarized-light microscopy,scanning electron microscope,X-ray diffraction,gel permeation chromatography,differential scanning calorimetry,etc.The result from FT-IR displayed that the basic functional groups of coix seed starch was similar to corn starch and potato starch.The number-average molecular weight,weight-average molecular weight,polydispersity,root mean square radius of gyration of coix seed starch were 139258 g/mol,262205 g/mol and 1.88,respectively.The morphology of coix seed starch granule was nearly roundness with smooth surface and grain size range from 4 to 31jμm.The coix seed starch granule has apparent at polarization cross lying at the center of the granule.The data obtained from X-ray diffraction exhibited that the crystalline type of coix seed starch was CA-type and the degree of crystallinity was 22.21%%which is lower to potato starch(24.56%)and corn starch(22.86%).The swelling power and solubility of coix seed starch is lower than potato starch but higher than corn starch,and not easy ageing.In addition,compare with corn starch and potato starch,the coix seed starch paste has low pasting temperature,high peak viscosity,indicating that coix seed starch held weak thermostability.These works will provide theoretical basis and the guiding principle for the production and development of coix seed starch.