Study On Preparation, Properties, Modification And Application Of The Coix Seed Starch

In this study,the skimmed Coix seed residue was used as the raw material to prepare thestarch by enzymic method,and its key technological parameters were optimized．Based on thefirst phase study,the surface morphology and the physicochemical properties of the Coix seedstarch were systematically observed and discussed．Meanwhile,the procedure for the productionof the Coix seed starch was modified with enzyme to prepare the porous starch which had highadsorption was also studied． And then, the Coix seed porous starch was used asmicro-encapsulation agent to develop powdered sesame oil,and the product had high storagestability and great convenience．The main results were as follows：(1) Study on preparation technology of the Coix seed starch by enzymic methodSkimmed Coix seed residue was used as the raw material to prepared the starch by enzymicmethod．On the basis of the single-factor experiment,the dose of Alkaline protease,enzymolysistemperature,enzymolysis pH,and enzymolysis time were determined as key factors,while theresidual protein content and the yield of the Coix seed starch were as test indexes．Theorthogonal test L9(34) design was used to optimize the technological parameters of preparation ofthe Coix seed starch．The results showed that optimum technological parameters were asfollows：the dose of Alkaline protease250u·mL^-1,enzymolysis temperature45℃,enzymolysispH11and enzymolysis time2.5h．On this condition,the yield of the Coxi seed starch was54.39%and the residual protein content was0.2302%,they were significantly superior to theCoix seed starch prepared by water extraction(p<0.01)．(2) Study on the physicochemical properties of the Coix seed starchThe chemical composition of the Coix seed starch,the surface morphology of starchgranules,and the physicochemical properties of the Coix seed starch pastes were systematicallyobserved and studied in this paper．The results showed that the dry sample of the Coix seedstarch contains99.619%starch,0.254%protein,0.022%fat and0.105%ash．The relativedensity of the Coix seed starch is1.376g·mL^-1．The Coix seed starch granules are rotundity andpolygon,and have apparent polarized cross lying in the center of the granules．The X_-raydiffraction patterns of the Coix seed starch granules showed that its structure belongs toC-type．The solubility and swelling power of the Coix seed starch increase as temperaturegrows,the gelatinization temperature is67℃-71.6℃．The transmission rate of the Coix seed starch paste is39.6%．The Coix seed starch paste has stronger freeze thaw stability and slowerretrogradation rate．Its retrogradation rate decreases under the acidic or alkaline environment,and increases under the neutral condition．According to Brabender viscosity curve,the thermalstability of the Coix seed starch paste is lower than the corn starch and stronger than the potatostarch (prepare the starch from corn and potato by enzymic method),and its cold viscositystability is the strongest．(3) Study on the technology of prepared the Coix seed porous starch with enzymic modificationBy the quadratic orthogonal rotary combination of experimental design,the regressionequations about water adsorption rate and oil adsorption rate of the Coix seed porous starch wereestablished as follows(the dose of glucoamylase X₁,enzymic modification time X₂,enzymicmodification temperature X₃,the water adsorption rate Y₁,the oil adsorption rate Y₂)：Y₁=126.00440+1.39323X₁+1.77898X₂+4.60172X₃-3.04755X₁2-3.70162X₂2-2.41115X₃2-1.21250X₁X₂-1.38750X₁X₃Y₂=78.14104+0.64303X₁+0.60775X₂+2.08053X₃-2.00127X₁2-1.22345X₂2-0.92293X₃2-1.48750X₁X₂-0.83750X₁X₃The results showed that the optimized parameters of prepared the Coix seed porous starchwith enzymic modification were as follows：The dose of glucoamylase500u·mL^-1, enzymicmodification time16hours,enzymic modification temperature58℃．Based on these conditions,water adsorption rate of the Coix seed porous starch was129.01%,oil adsorption rate was79.87%,and there were no significant differences between the theoretical value (128.20%and79.30%) and the actual measured value(P>0.05)．(4) Application of the Coix seed porous starch in the micro-encapsulation of powdered sesameoilThe Coix seed porous starch was used as the micro-encapsulation agent to preparepowdered sesame oil．Based on the quadratic orthogonal regression design,the optimizedprocess parameters for micro-encapsulation of powdered sesame oil were as follows：theproportion of sesame oil to wall materials0.75:1(g·g^-1),the embedding time91.56min,thepowdered sesame oil was developed based on these conditions obtained the best embedding rate51.23%,and the theoretical value of the embedding rate was51.38%．There existed nosignificant differences in statistics(P>0.05)．To compare with the liquid sesame oil and the powered sesame oil of the corn porous starch in storage stability test,the results showed that：the powdered sesame oil with the Coix seedporous starch had the best stability．The powdered sesame oil with the Coix seed porous starchwere exposed to62±1℃for12days (to be equivalent to22℃for192days),its acid value andperoxide value were0.91mg·g^-1and1.64mmol·kg^-1,its quality was complied with nationalstandard of the sesame oil (GB8233-2008),and the two indexes were significantly lower than thepowered sesame oil which prepared with the corn porous starch (p<0.05) and the liquid sesameoil (p<0.01)．...