Preparation And Properties Of Maize Starch-based Film Materials

As a natural renewable resource,starch has attracted more and more attention in the field of food packaging materials due to their rich source,green safety,and biodegradability.Starch has good development prospects,and the research on starch-based materials with excellent performance has become a hot topic at home and abroad.In this thesis,starch-based materials were obtained by enzymatic debranching and etherification,and as raw materials,starch films were prepared.On this basis,other additives were added to gradually improve the performance of starch film materials,and the relevant mechanism was preliminary explored.This study provides a theory and guidance for the future development of starch-based materials and the related applications.Firstly,starch-based materials were prepared by enzymatic debranching or etherification,and their properties were analyzed.Compared with the original starch-based materials,the amylose content of the enzymatic debranching starch-based materials was increased increased from 20.8%to 58.3%,the starch granules were severely damaged,the gelatinization temperature was increased,the crystallinity and the molecular weight were both decreased.The MS(molar degree of substitution)value of the etherified starch-based materials was 0.20,the granule morphology changed,the gelatinization temperature,the molecular weight and crystallinity were all decreased.The MS value of the enzymatic debranching-etherified starch-based materials was 0.17,the amylose content increased to 61.8%,the particle destruction was severe,the gelatinization temperature increased,the molecular weight reduced obviously,and the crystallinity decreased.Secondly,starch film materials were prepared with different starch-based materials as raw materials and glycerin as plasticizer.Compared with the original starch film,the barrier properties of the enzymatic debranching starch film were improved,the water vapor permeability coefficient was reduced by 15.2%,the thermal stability was increased,and the surface was smooth,but the mechanical properties were poor,the elongation at break was only 8.4%.The surface of the etherified starch film was dense and smooth,and the elongation at break increased more than twice,but the mechanical strength was reduced by 39.4%.The barrier properties and thermal stability were also poor.The increase of amylose content is conducive to the formation of a dense structure of the starch film,and the hydroxypropyl group could act as an internal plasticizer.Under the influence of both,the enzymatic debranching-etherificated starch film had better performance.The mechanical strength was increased by 52.5%,the elongation at break was reduced by 33.0%,the water vapor transmission coefficient was reduced by 8.7%.In addition,the oxygen barrier performance and thermal stability were also improved.Then,on the basis of the above-mentioned enzymatic debranching-etherification starch film materials,citric acid was added to further improve the material properties,especially the water blocking ability,and its structural characteristics were analyzed.When the starch-based material concentration was 3%,the glycerol content was 30%,the processing temperature was95°C,and the citric acid content was 10%,the prepared starch-based composite film had better performance.The tensile strength is 4.11 MPa,the elongation at break is 38.1%that increased by 45.2%,and the water vapor permeability coefficient is 0.51 g·mm/(m~2·h·kPa)which reduced by 39.3%.Structural analysis results showed that it had a relatively open crosslinked network structure,in which the starch chain was preferentially combined with the ester formed by citric acid and glycerin,but the hydrolysis of citric acid could lead to a weakened network structure.Finally,on the basis of the above-mentioned compound modified starch film materials,the antibacterial agent nano ZnO-chitosan was further added to improve the antibacterial properties.In this nano-antibacterial agent,the chitosan accounts for about 43.2%,ZnO accounts for about 56.8%,and it had a good antibacterial effect.The film properties were significantly influenced due to the interaction between nano ZnO-chitosan and starch system,and the aggregation of nano ZnO-chitosan at high concentration.When the addition amount was 3%,the prepared antibacterial starch composite film material had better performance.Under this condition,the tensile strength was 12.79 MPa which was increased by more than 2times,and the elongation at break was 21.4%.The water vapor transmission coefficient was0.46 g·mm/(m~2·h·kPa)that was futher decreased,the oxygen barrier capability was enhanced,and the inhibition rates for E.coli and S.aureus were 55.1%and 91.2%,respectively.