Study On Preparation,Properties And Application Of Chemical Modification Corn Starch Under Microwave Assistance

Starch is a kind of polymer formed by the alpha-D-glucose bonding via glycosidic bond,which with different sources have their own unique physicochemical properties.Therefore,it is necessary to modify the structure of natural starch to meet different needs.In this study,maize starch was modified by physicochemical treatment.The response surface methodology was used to optimize the synthesis process of the product.Acetate corn starch and hydroxypropyl corn starch with different degree of substitution were prepared,which used as raw materials,was determined in the differences and connections of physicochemical properties such as transparency,hydrophilicity and hydrophobicity,freeze-thaw stability.The experimental results were as followed:（1）Acetate corn starch was prepared with different degree of substitution under microwave assistance.A three-level-three-factorial central composite design using response surface methodology was employed to optimize the reaction conditions.The optimal parameters are as follows:amount of acetic anhydride of 12%,radiation time of11 min,and microwave power of 100 W.These optimal conditions were confirmed that the degree of substitution of acetate starch was 0.0691.The physicochemical properties of acetate corn starch were studied.The results showed that the transparency,condensation volume ratio,hydrophilicity and lipophilicity of acetate corn starch increased with increasing of substitution degree,which were 4.0%to 12.1%,21.11%to31.78%,0.73 g/g to 0.91 g/g and 0.66 g/g to 0.88 g/g,respectively and the rate of water evolution decreased from 44.9%to 33.3%.Fourier transform infrared spectroscopy showed that acetyl group was successfully introduced.Scanning electron microscopy showed that microwave pretreatment and group introduction made the surface of starch granules locally porous and rough.Differential scanning calorimetry showed lower onset temperature,peak temperature,conclusion temperature and enthalpy than that of native corn starch.X-ray diffraction showed that modification did not change the crystalline type of starch,which was still A type.The vitro digestibility of acetate corn starch indicated that compared with native corn starch,the content of rapidly digestible starch decreased significantly from 63.70%to 50.20%,the content of slowly digestible starch increased from 19.47%to 21.82%,and the content of resistant starch increased from16.84%to 27.98%.（2）The microwave assisted conditions of hydroxypropyl corn starch were studied.Response surface methodology was used to optimize the reaction conditions of three-level-three-factorial center composite design.The optimum parameters were as follows:the additive amount of propylene oxide was 8%,the radiation time was 6 min,and the microwave power was 300 W.The optimal degree of substitution of hydroxypropyl corn starch was determined by the optimal conditions predicted by response surface methodology,which was 0.0711.The physicochemical properties of hydroxypropyl corn starch were tested.The analysis of physicochemical properties showed that with the increase of the degree of substitution of hydroxypropyl corn starch,the transparency（4%to 8.81%）,the volume ratio of the condensing volume（21.11%to33.11%）,the hydrophilic（0.73 g/g to 2.46 g/g）,and the hydrophobicity（0.67 g/g to 1.01g/g）,and the water evolution rate（46.91%to 36.16%）decreased.Fourier transform infrared spectroscopy showed that the enhancement of peak intensity at 1149 cm^-1indicated the successful introduction of hydroxypropyl group.Scanning electron microscopy showed that the surface morphology of corn starch was affected to some extent.Differential scanning calorimetry showed after hydroxypropyl,the enthalpy and phase change temperature decreased compared with native corn starch.X-ray diffraction showed modification did not change the crystalline type of starch,which was still A type.The vitro digestibility of hydroxypropyl corn starch was studied.Compared with native corn starch,the content of rapidly digestible starch of hydroxypropyl corn starch decreased significantly from 63.70%to 52.61%,slowly digestible starch content increased from 19.47%%to 22.89%,and resistant starch content increased from 16.84%to 27.45%.（3）The noodle quality of acetate corn starch and hydroxypropyl corn starch was studied.The L values of native wheat noodle,native corn starch-wheat noodle and acetate corn starch-wheat noodle were 83.42,83.99 and 85.73 respectively.With the addition of native corn starch and acetate corn starch,the water absorption of noodles was better than that of native wheat noodle,and the loss rate of dry matter was reduced.The hardness,elasticity,adhesiveness and chewiness of native corn starch-wheat noodle and acetate corn starch-wheat noodle were decreased to some extent compared with native wheat noodle.The breaking force of native corn starch-wheat noodle and acetate corn starch-wheat noodle decreased in turn and lower than that of native wheat noodle,while the breaking distance of native corn starch-wheat noodle and acetate corn starch-wheat noodle increased in turn and were higher than that of native wheat noodle.The L values of native wheat noodle,native corn starch-wheat noodle and hydroxypropyl corn starch-wheat noodle were 83.42,83.99 and 85.49 respectively.With the addition of native corn starch and hydroxypropyl corn starch,the water absorption of noodles was better than that of native wheat noodle,and the loss rate of dry matter was reduced.The hardness,elasticity,adhesiveness and chewiness of native corn starch-wheat noodle and hydroxypropyl corn starch-wheat noodle were decreased to some extent compared with native wheat noodle.Hydroxypropyl corn starch-wheat noodle had lower breaking force and higher breaking distance than that of native wheat noodle.