Study On Preparation And Application Of Pullulanase Modified Potato Starch Composite Membrane

Starch-based degradable plastics are a type of plastics with natural starch or starch derivatives as the main matrix.Starch can be produced continuously and can be completely degraded.It is regarded as an effective substitute for petroleum-based plastic products.China is a large potato producer,and a lot of waste is generated every year due to improper storage or processing conditions.However,potato starch has the advantages of low gelatinization temperature,stable paste,high transparency,strong adhesion,and strong film-forming properties.Therefore,it will be one of the effective ways to solve this waste if it is used as a raw material for degradable plastics.However,the polyhydroxy structure of starch leads to defects such as poor toughness and sensitivity to environmental humidity after film formation.To improve these defects and expand its scope of application,this paper uses potato starch as the matrix and improves the mechanical properties,optical properties and hydrophobic properties of starch films through composite modification methods.At the same time,optimize the formulation and improve the production process,and study the preservation effect of potato starch composite film on toast bread.The main research results are as follows:(1)The effect of pullulanase on the performance of potato starch composite membrane was discussed.Firstly,I discussed the effects of the types of plasticizers(carbonamide and formamide)and their proportions,the types of reinforcing agents(starch nanocrystals and nano-zinc oxide)and the proportions on the mechanical properties and optical properties of the composite film by single-factor test.Then the effects of the amount of pullulanase,the reaction temperature,the reaction time,and the pH value of the solution on the tensile strength of the composite film were discussed through orthogonal experiments,and its mechanical properties,optical properties,barrier properties,thermal stability,microstructure and Infrared spectroscocopy was characterized.The experimental results show that the amylose content of potato starch is increased by 171.8% after pullulanase debranching treatment.Compared with the non-enzymatic composite film,the composite film prepared by the best process has mechanical properties,optical properties and barrier properties obviously improved,including tensile strength increased by 19.0%,elongation at break increased by 42.8%,transparency increased by 5.6%,haze decreased by 206.8%,water vapor transmission coefficient decreased by 98.4%,oil permeability coefficient decreased 52.5%.(2)The effects of the two methods of organic reagent hydrophobic modification system immersion method and laurate esterification modification method on the contact angle of potato starch composite film were discussed.In the organic reagent modification method,the effect of potato starch composite membrane immersion time in the octadecyltrichlorosilane-nhexane system on the contact angle,mechanical properties and optical properties of the composite membrane was discussed.The experimental results show that when the modification time at 9h,the contact angle reaches a maximum of 154.1°.In the laurate esterification modification method,the single factor test was used to explore the effects of the amount of lauric acid,Tween 80,reaction time and reaction temperature on the contact angle of potato starch composite film.The orthogonal test was designed based on the results of the single factor test with the contact angle as the index,the experimental results show that when the composite film is prepared by the best process,the contact angle of the composite film reaches 100.3°,and its mechanical properties and barrier properties are also significantly improved.(3)The potato starch composite film was prepared by the optimal process,and three types of packaging methods for toast: polyethylene single film,potato starch composite film/polyethylene(outer/inner layer),and polyethylene/potato starch composite film to the freshness effect of bread were discussed.The toast bread’s sensory quality,total bacterial count,acid value and texture characteristics were used as indicators to characterize the freshness of toast bread.The experimental results show that under the same storage conditions,various indicators show that the polyethylene/potato starch composite film has the best preservation effect.On the 11 th day of storage,the sensory score,the total number of colonies,and the acid value reached the standard values.(4)Compare the degradation rates of potato starch film,enzymolysis potato starch film,plasticized enhanced potato starch enzymolysis film and lauric acid modified potato starch enzymolysis film.The experimental results show that on the 90 th day,the degradation rates of the three films are above 80%,and the degradation rate of the potato starch composite film with plasticizers and enhancers added is 90.70%,which shows that the plasticizers and enhancers will increase degradation rate of thermoplastic potato starch film.