Effect Of Amylose/Amylopectin Structure Of Starch On Microwave-assisted Esterification And Its Application In Hydrogels

Starches are widely distributed in nature with the advantages of renewable,degradable and low cost,and have been widely used in both food and non-food industrial fields.As a consequence of unfavorable properties of the native starch,like poor solubility and high hydrophilicity,and their poor resistance to extreme processing conditions such as high temperature and shear that are frequently encountered in the industry.Starches are therefore modified to overcome these shortcomings and to increase their processing properties and performances.Wet method,organic solvent method,and dry method are common modification methods.Among them,the organic solvent method has weakness such as low reaction efficiency and side reactions caused by the hydrolysis of organic reagents.As a kind of dry method,microwave radiation technology has the advantages such as: fast and simple,strong penetration,good heating uniformity,etc.It has been widely used in the physical and chemical modification of starch.When applied in the preparation of esterified starch,it can effectively improve the reaction rate and shorten the reaction time.Hydrogel has a three-dimensional network system with the ability to absorb large quantities of water,and has a wide range of applications in transportation,agricultural controlled and slow-release,etc.Crosslinking agents are often used in the preparation of hydrogels,which can cause the non-uniformity of the hydrogel network structure,reduce its transparency and mechanical strength.The synthesis of hydrogel with uniform structure has important theoretical significance and practical value.This experiment is based on microwave radiation technology to study the influence of microwave and conventional heating on starch structure and the influence of starch microstructure on microwave-assisted esterification reaction.The heating mechanism and esterification reaction mechanism were explored,which could provide theoretical basis about starch's dry modification.On former basis,the maleic anhydride starch ester was used as the reaction materials to prepare hydrogels,which provides a theoretical basis for improving the non-uniformity of the hydrogel.It was first time to systematically study the effect of starch microstructures,especially different amylos/amylopectin ratio,on the microwave-assisted esterification reaction.Cornstarches with different amylos/amylopectin ratios,waxy(0/100),Maize(23/67),G50(50/50)and G80(80/20)were used in this work.The relevant research results are as follows:1?After microwave radiation/conventional heating treatment,the chemical group type and crystal form of starch did not change,and the morphology of the granule was partially changed;The crystalline structure was destroyed,and the interaction between amylose and between amylose and amylopectin within the granule was strengthened,and stable and high temperature resistant microcrystals were formed;The destruction and rearrangement of microcrystals in the amorphous area occured simultaneously;Compared with conventional heating,microwave radiation had more impacts on the physical and chemical properties of starch.With the increase of amylose,the sensitivity of starch to microwave radiation increased.Amylose had more polar molecules such as hydroxyl groups and water,and was more sensitive to microwave.2?The esterification reaction mainly occured on the surface and amorphous area of starch granules.Microwave-assisted dry method generally did not affect the granule structure;The degree of substitution of maleic anhydride starch ester increased with the increase of amylose content,and the degree of substitution of acetate starch increased with the increase of amylopectin content;maleic anhydride had a greater effect on the crystallinity of esterified starch than acetic anhydride,and the starch modified by maleic anhydride had a higher degree of generation,indicating a higher degree of reaction.3?The maleic anhydride starch ester-based hydrogel was successfully prepared in a mixer suitable;The proportion of hydrophilic side chains and the grafting rate of hydrophilic groups in the hydrogel increased with the increase of initiator content,and the degree of substitution had little effect on it;Increasing the amount of initiator increased the content of polyacrylamide side chains,and the water absorption of the hydrogel also increased;With the degree of substitution increases the crosslinking density increases,and the length of polyacrylamide side chains was inhibited.Thus,the water absorption ratio of the hydrogel decreased.