Preparation Of Chitosan/Zein Composite Coating Material And Its Application In Preservation Of Blueberry

The food fresh-keeping materials prepared by single chitosan have some defects in mechanical properties and hydrophobic properties,so their application in the field of food fresh-keeping is greatly limited.The preparation of composites by physical blending to make the components interact with each other can not only improve the defects of single chitosan fresh-keeping materials,but also achieve the purpose of synergism.and then improve the utilization of chitosan resources and the application potential in the field of food preservation.Blueberry has high nutritional value,but because of its thin peel and poor shelf life,blueberry sales radius and shelf life are short,and the expansion of industrial scale is limited,so the study of blueberry fresh-keeping technology is of great significance to the development of blueberry industry.In order to solve the above problems,edible composite coating materials were prepared by using chitosan and Zein as substrates.Through single factor and response surface optimization experiments,the optimum technological conditions for the preparation of chitosan / Zein composite coating materials were determined.The physical and chemical properties of the composite coating materials were characterized.The composite coating material was applied to the storage and preservation of blueberry,and the physiological and biochemical indexes and antioxidant activity of blueberry were determined and evaluated systematically.In order to improve the storage quality of blueberries at room temperature,prolong the shelf life of blueberries,and provide a theoretical basis for expanding the industrial scale of blueberries.Through the study,the following conclusions are drawn:The main results are as follows:(1)Edible composite coating materials were prepared with chitosan and Zein as substrates.Taking the tensile strength and elongation of the composite coating material as the investigation index,the effects of the compounding ratio,the amount of glycerol and the volume of coating solution on the mechanical properties of the composite coating material were studied.On the basis of single factor test,response surface optimization test was carried out.Finally,it is determined that the best preparation process of the composite coating material is as follows: the ratio of Zein to chitosan is 1:4,the addition of glycerol is 0.25%,and the volume of the film coating solution is 25.2 mL.The tensile strength of the composite coating material is 9.91 MPa and the elongation is 19.33%.(2)the physical and chemical properties of the composite film were characterized by Fourier transform infrared spectrum,X-ray diffraction spectrum,scanning electron microscope,film thickness,light transmittance,water vapor transmittance and surface contact angle.Compared with the single chitosan film,the Fourier transform infrared spectrum shows that the characteristic peak shifts and the protein absorption peak appears,while the X-ray diffraction spectrum shows that the diffraction peak is obviously weakened.This is due to the cross-linking reaction between chitosan and Zein in the process of preparation,which enhances the stability of the composite coating material.The scanning electron microscope shows that the surface of the composite coating material is smoother,denser and without obvious cracks.In the case of no significant difference in film thickness,the light transmittance and water vapor transmittance of the composite coating materials were51.09 ±0.1% and 9.62 ±0.02 mg cm2 d-1,respectively,which were lower than those of single chitosan film.The surface contact angle of the composite coating material is 86.17 °,which is 31.72 °higher than that of the single chitosan film.The results show that the composite film material has stronger mechanical properties and hydrophobic properties.(3)the storage and fresh-keeping experiment of blueberry was carried out by three methods: no treatment,single chitosan film treatment and compound coating material treatment.On the 15 th day of storage,the weight loss rate of blueberry treated with composite coating material was 29.65%,the decay rate was 8.87%,the total number of colonies was 9.4 log(CFU/g),the respiratory intensity was 0.86%,the content of soluble solids was 12.76%,the content of vitamin c was 69.63 mg/g,and the content of anthocyanin was 0.93 mg/g.The results showed that the composite coating material could effectively reduce the weight loss rate,decay rate and total bacterial count of blueberry,inhibit its respiratory intensity,and delay the decreasing trend of soluble solids content,Vc content and anthocyanin content of blueberry.Therefore,chitosan / Zein composite coating material has a good fresh-keeping effect on blueberries,can effectively inhibit the decline of physiological and biochemical indexes of blueberries,so as to prolong the shelf life of blueberries.(4)the antioxidant activity of blueberry was tested by three methods: no treatment,single chitosan film treatment and composite coating material treatment.The results showed that on the 15 th day of storage,the total phenol content,superoxide dismutase(SOD),DPPH radical scavenging rate and peroxidase activity(POD)were 1.96 mg/g,72.17 U / g FW,43.74% and 1.66 U / g min,respectively.It was 1.15 times,1.21 times,1.16 times and 1.32 times higher than that of single chitosan film group,respectively.Therefore,chitosan / Zein composite coating material has a better protective effect on the antioxidant activity of blueberry.