| In this paper,natural corn starch was used as experimental material to modify corn starch by the combination of a-amylase,?-amylase and transglucosidase.The structure and morphology of corn starch granules were preserved while changing their molecular structure,and the physicochemical and digestive properties of enzyme-modified corn starch were further studied.The main findings are as follows:1.The enzyme-modified starch granules still retain the original starch granule morphology,and there is a typical optical birefringence phenomenon.Compared to natural corn starch,starch granule cracks and dark spots in the umbilical point increase after enzyme treatment.There are many pores on the surface of natural corn starch granules.After enzyme modification,the pores on the surface of starch granules form larger pores.With the increase of enzymatic hydrolysis time,the number of pores on the surface of the granules increases gradually,and the depth of the pores increases.2.Different enzyme-modified starches were prepared according to different enzymatic hydrolysis time(2 h,4 h,6 h,8 h,10 h,12 h).Compared with natural corn starch,the ratio of A chain and B1 chain increases after enzyme modification,while the ratio of B2 chain and B3 chain decreases.With the increase of enzyme reaction time,the proportion of A chain and B1 chain increased from 25.12%and 52.44%to 29.58%and 55.53%,respectively.And the proportion of B2 chain and B3 chain decreased from 13.96%and 8.48%to 8.16%and 6.73%,respectively.3.The degree of branching of the enzyme-modified starch is between 7.8%and 12.1%,which is higher than 5.3%of natural corn starch.4.The peak of the diffraction peak of corn starch granules after enzyme modification showed no obvious change,and still showed A-type structure,but the intensity of the characteristic peak of diffraction decreased.The relative crystallinity of the enzyme-modified starch is between 38.13%and 43.52%,which is lower than 48.23%of the natural corn starch.5.RDS,SDS and RS of natural corn starch were 68.90%,20.60%and 10.50%,respectively,and EGI was 75.08.The SDS and RS contents of the enzyme-modified starch increased from 24.74%and 14.39%to 29.17%and 18.77%,respectively,while the RDS content and EGI decreased from 60.87%and 59.71%to 52.06%and 46.37,respectively.6.The solubility and transmittance of natural corn starch were 11.34%and 20.86%,respectively.The solubility and transmittance of the enzyme-modified starch increased from 21.51%and 33.72%to 31.15%and 41.45%,respectively,with the extension of enzymatic hydrolysis time.7.The conversion temperature(To,Tp,Tc)of the enzyme-modified starch increased compared with the natural corn starch,and with the enzymatic hydrolysis time increased from 69.21?,72.59? and 78.42? to 71.87?,75.83?,80.70?.The gelatinization temperature range(Tc-To)of natural corn starch is 12.09?,while the gelation temperature of the enzyme-modified starch decreased from 11.02? to 8.83? as the enzymatic hydrolysis time prolonged.The gelatinization enthalpy(AH)of natural corn starch was 7.40 J/g,while the AH of enzyme-modified starch showed a trend of increasing with the increase of enzymatic hydrolysis time.When the enzymatic hydrolysis time was extended to 12 h,?H increased to 8.99 J/g.8.The viscosity of natural corn starch and enzyme-modified starch decreased with the increase of shear rate,but the viscosity of enzyme-modified starch was significantly lower than that of natural corn starch,and the viscosity decreased with the prolongation of enzymatic hydrolysis time.The storage modulus and loss modulus of natural corn starch gradually increase with the angular frequency,and the storage modulus is always far greater than the loss modulus over the entire frequency range.The storage modulus and loss modulus curves of the enzyme-modified starch are similar to those of natural corn starch,but significantly lower than that of natural corn starch,and gradually decrease with the prolongation of enzymatic hydrolysis time. |
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