Study On Controllable Fabrication Of Edible Coating By Layer-by-layer And Its Application

Due to the characteristics of safety,environmental protection and sustainability,edible coatings continue to attract people’s attention in the field of food preservation.However,a good fruit and vegetable preservation coating needs to meet many requirements,such as good antibacterial activity and mechanical properties,precise balance of gas and water vapor penetration,and very good adhesion.It is difficult for a single-component and structured coating to fully meet these requirements.Layer-by-Layer（LbL）is a method that can be actively controlled to prepare composite coatings,which can give full play to the advantages of each combination of materials to adjust the performance of the coating,with complementary materials,structure and performance controllable.This paper mainly uses the advantages of LbL,through the LbL of chitosan（CS）and sodium alginate（SA）to prepare the performance controllable edible coating,realize the adjustment,maintenance and improvement of the performance of fruit and vegetable fresh-keeping coating,in order to solve the practical problems in the application process of coating,so as to achieve the purpose of extending the shelf life.The main research contents are as follows:In view of the lack of methods to control the thickness of edible coatings,the LbL of CS and SA has been studied to achieve precise control of coating thickness to adjustment of coating performance.The research on the coating formation mechanism,thickness growth law and physical properties of the coating shows that the assembly process of CS and SA is electrostatically driven and the film is formed under the combined action of hydrogen and ionic bonds after drying;the thickness of the coating has the fastest growth under the conditions（salt concentration:0.1 mol/L,p H=4 of SA and CS）.By adjusting the assembly concentration and number of times,the coating can be accurately prepared with a thickness in the range of 0.2-36μm.The LbL based on CS and SA can prepare the coating thickness to meet the spontaneous air conditioning requirements of fruits and vegetables according to the prediction.Based on the spontaneous air conditioning model,it is predicted that in the coating combination,（SA₁/CS₁）₃,(SA_1.5/CS_1.5)₃ and(SA_1.5/CS_1.5)₂ have better effect on strawberry,sugar orange and banana respectively.The shelf life at room temperature was extended from 2,8 and 6 d to 4,12 and 10d,respectively.Aiming at the degradation of coating performance caused by the damage of the coating,the repair ability of the LbL coating prepared by CS and SA was studied to achieve the maintenance of the coating performance.The research results show that the（SA/CS）_ncoating can have repairing ability,and its repairing ability is mainly derived from the relative movement of the molecular chain after the addition of water;the mechanical properties,water transmission rate,and oxygen transmission rate of the coating were 97%,95%,and 63%of the intact coating,respectively.Compared with the control group,the（SA/CS）3 coating reduced the spoilage index of strawberries by 22%,reduced the weight loss by 9.23%,delayed the peak appearance of soluble solids from 1 d to 4 d,and slowed down the antioxidant capacity and the accumulation of malondialdehyde.The coating can maintain its high barrier properties through healing,thereby reducing the adverse effects of coating damage on strawberries.In view of the lack of antibacterial ability of LbL coatings prepared by CS and SA,citral with antibacterial activity was added to the coating to improve the performance of the coating.The influence of the introduction of citral on the performance of the coating and the retention and release performance of the LbL structure on citral were studied.The results show that citral can enhance the barrier performance of LbL coatings,and the layered structure of LbL can improve the release and retention of citral of the coating;the retention rate and release rate of citral can be adjusted by changing the loading position of citral.The release mechanism of citral in the film is mainly Fick diffusion,and the LbL film is still affected by the swelling mechanism;the Peppas model can be used to simulate the release of citral in the LbL film.Compared with the control group,the S/C-L/S/C/S/C coating containing citral could reduce the decay index of Strawberry by 77.53%,and prolong the shelf life of coated strawberry to more than 7 days at room temperature.