Preparation Of Hyperbranched Maize Starch By Transglucosidase And Its Effect On Selfhealing Performance On Microcracks In Starch Film

In recent years,the pollution of food packaging materials to the environment has attracted increasing attention.As human beings are extremely continuously consuming limited non-renewable resources,the development of cost-effective,environmentalfriendly,green and degradable starch-based food packaging materials has become a global trend.At the same time,the solutions for aging and reducing the service life of starch-based materials have been continuously paid attentions by researchers in recent years,and the self-healing properties of materials have attracted increasing attention due to their convenience and novelty.In this study,gelatinized wheat starch was branching-structurally modified by transglucosidase to explore the mechanism of transglucosidase treating on wheat starch.Subsequently,the modified starch with higher branching degree was prepared by modifying the structure of waxy maize starch by double enzymatic method with α-amylase and transglucosidase.Second,native waxy maize starch(WMS)and enzymetreated waxy maize starch(EWMS)were encapsulated using polylactic acid(PLA)and polyvinyl alcohol(PVA)to prepare microcapsules.Finally,the two prepared microcapsules were added into corn starch film to prepare a corn starch film-based material containing microcapsules,then the microcracks were produced by the aging process,at where the self-healing reactions started.The specific results are as follows:(1)The branching degree was significantly increased by 27.36% after the gelatinized wheat starch was treated with transglucosidase(TG),and the average chain length was decreased by 21.06%.The starch showed the domination of amorphous region as the enzyme treatment time increased.While the rheological properties changed from viscoelastic to viscous,and the mobility of water in retrograded enzyme-treated starch increased with the increase of treatment time.The retrogradation kinetics showed that the starch aging degree was decreased by 14.22%.The results demonstrate that TG hydrolyzed α-1,4-glycosidic bonds and transglycosylate the hydrolyzed short starch chains to generate new α-1,6-glycosidic bonds,which provided a theoretical basis for the following specific applications;(2)The branching degree increased by 21.35% after WMS was treated by α-amylase(AA)and TG combined-enzyme method,and the average chain length decreased by18.36%.The sample treated by AA for 3h followed by TG treating for 16h(EWMS-16)had the highest apparent viscosity and the lowest relative crystallinity under high shear stress.Hence,EWMS-16 can be applied to microcapsule preparation;(3)Degradable polylactic acid(PLA)was selected as the wall material for microcapsules in this study.Compared to that of the PLA-microcapsules encapsulating WMS(WMSMCs),the average particle size of TGWMSMCs was 3.487 μm,while the average particle size of WMSMCs was 5.266 μm.The microcapsules were spherical,and the shell thickness was about 0.5 μm through the SEM photos.The starch core material dyed with Rhodamine B in the microcapsules filled the entire wall material,and the shape was consistent with the shell of the microcapsules.The microcapsules contained no residual dichloromethane used as the wall material solvent.The encapsulation rates of WMSMCs and TGWMSMCs were 48.33% and 40.08%,respectively.The microcapsules prepared above can be used for self-healing research of starch-based film materials;(4)In this thesis,the self-healing properties of two microcapsules added into corn starch-based materials were investigated.The experimental results showed that different degrees of microcracks were observed in the aged starch film,the microcapsules were ruptured and the esterification reaction occurred.The thermal decomposition rate,water vapor permeation rate and mechanical strength of the aged TGWMSMCs starch films were significantly lower than those of the aged WMSMCs starch films,and the healing efficiency of adding TGWMSMCs was higher than that of adding WMSMCs,indicating that the increased branching degree of WMS after TG treatment resulted in the increase of healing site point.The above results demonstrated that TG had a certain effect on the self-healing properties of starch film microcracks.This outcome would provide ideas for solving the problem of short life of starchbased green degradable materials caused by aging and brittle during the usage,and confirms that WMS can heal starch-based materials to a certain extent as a healing agent.The feasibility of the higher healing efficiency caused by EWMS as healing agent treated by TG to get higher starch branching degree would provide a new perspective for extending the life of starch-based green degradable materials,which is of great significance.