| The high amylose film has some advantages in its properties compared to the ordinary starch film.However,the high gelatinization temperature of high amylose starch leads to poor processing performance.In order to improve its processing performance and prepare high amylose film with excellent performance,hydroxypropyl group was modified in different degrees of high amylose corn starch in this paper,and hydroxypropyl high amylose corn starch film was prepared by solution casting,besides,the effect of compound plasticizer on the properties of hydroxypropyl high amylose corn starch films with different degrees were studied.In addition,the effects of fatty acids with different chain lengths and monoglyceirdes on the properties of starch films were studied.The properties of modified starch were characterized by scanning electron microscopy?SEM?,polarizing microscope and X-ray diffraction?XRD?.Differential scanning calorimetry?DSC?,contact angle test?CA?and low field nuclear magnetic resonance?LF-NMR?in combination with mechanical properties,water permeability and light transmittance were used to characterize the properties of the starch films.The main results were as follows:1.Hydroxypropylation had a significant effect on the physicochemical properties of high amylose corn starch.Hydroxypropylated modification significantly reduced the gelatinization temperature of high amylose corn starch and improved its processability,and the higher the degree of substitution?DS?,the lower the gelatinization temperature.SEM showed that after hydroxypropylated modification,the starch granules were broken and the surface showed a concave and convex shape,slightly contracted,the shape became irregular,the angle appeared,and the size of starch granules became larger.Polarizing microscope photographs showed that the polarized cross was weakened after modification.XRD showed that hydroxypropylated modification with low degree of substitution did not change the crystalline form of starch,and still remained B type crystalline structure,and hydroxypropylated modification with high degree of substitution destroyed its crystal structure.Hydroxypropylation of starch mainly occured on the surface of starch and in the non-crystalline region of starch granules,and then gradually developed into the crystalline area.2.Different DS had a significant impact on the performance of hydroxypropyl amylose starch film.Hydroxypropylated modification increased the flexibility of the films.With the increased of DS,E increased from 11.07%to 85%.At the same time,the transmittance increased,at the wavelength of 600 nm,the transmittance increased from 29.95 to 63.95.In addition,Tp and?H were increased.However,the increase of hydroxypropylation degree reduced the TS from 21.33 MPa to 5.08 MPa,and because of the hydrophilicity of hydroxypropyl group,the hydrophilicity of the starch films increased.3.Using glycerol?G?and glycerol diacetate?GD?as composite plasticizer and changed the proportion had a significant impact on hydroxypropyl amylose corn starch film.The addition of GD made the flexibility of starch film enhanced while the TS decreased,and it had different effects on the high DS starch films.High addition of GD made the TS of high DS starch films increased.Using G and GD as composite plasticizers,the water resistance of starch films was greatly improved.With the addition of 18G12GD,the WVP value was 1.67×10-1212 g·cm·cm-2·s-1·Pa-1.In addition,the transmittance of the starch films increased significantly.The properties of starch films with 22G8GD as plasticizer were better.4.Choosing hydroxypropyl high amylose corn starch with 0.41 degree of substitution as material to prepared starch films,2%?w,w?fatty acids and monoglycerides had a significant effect on the performance of starch films.The length of carbon chain,the property of lipid and the effect of starch composite were affect the performance of starch films.The TS and E of the starch films were enhanced by lauric acid?LA?and glyceryl monolaurate?GML?,respectively.After adding fatty acids and monoglycerides,the water resistance of the starch films increased significantly.The LA and GML made the WVP of the composite film lower,which were1.87×10-1212 g·cm·cm-2·s-1·Pa-1 and 1.67×10-1212 g·cm·cm-2·s-1·Pa-1,respectively.Fatty acid or monoglyceride covered on the surface of starch molecules,so that enhanced the compactness of starch film and decrease the transmittance of starch film.SEM showed that the starch films prepared by LA or GML combined with hydroxypropyl high amylose corn starch with 0.41 degree of substitution were uniform,smooth and regular,and the performance of the starch films were better. |
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