Research On Mango Preservation Method Based On Cinnamon Essential Oil Active Composite Film And Electrostatic Spraying Technology

Mango has important health benefits and economic value,and has become one of the tropical fruits with the highest planting,production,and consumption in the world.As a respiratory climacteric fruit,mangoes undergo characteristic ripening changes after harvest,leading to problems such as aging,browning,and spoilage.The existing preservation technologies（cold chain,controlled atmosphere,etc.）can provide excellent preservation,but they are not widely available due to high operating costs and high energy consumption of equipment.Edible coating preservation technology can form a protective layer on the surface of fruits,which is a green and economical preservation method.Many studies have incorporated essential oils into a single coating matrix to enhance the antibacterial and preservation effects of the coating,but the essential oils suffer from a lack of light stability and volatility,which is not conducive to the long-term preservation of coated fruits.In addition,the current common coating methods（dip coating,brush coating and spray coating）have low transfer efficiency of the coating solution and have difficulty in forming a uniform and complete coating on the smooth skin of mangoes.In order to address the shortcomings of existing research,Cinnamon essential oil（CEO）was selected as an antioxidant and antibacterial agent in this study,a new bilayer film with high photostability and low CEO volatility was prepared by selecting Ti O₂ as the light barrier and using Pickering emulsion to encapsulate the CEO.The electrostatic spraying technology was used to improve the coating quality and transfer efficiency to achieve the efficient preservation of mangoes.This study provides new ideas and references for the development and research of new methods of cling coating.The main research contents are as follows:（1）Preparation and characterization of CS anti-UV bilayer films loaded with CEO-Ti O₂In response to the problem that CEO has insufficient photostability,Ti O₂ was selected as the UV blocker to construct a bilayer film system in this study.Bilayer films with UV resistance were prepared by adding CEO to a chitosan（CH）matrix as the active inner layer and Ti O₂ to a sodium alginate（SA）matrix as the protective layer.The successful preparation of the bilayers was confirmed by Scanning Electron Microscope（SEM）and Fourier transform infrared spectroscopy（FT-IR）.The addition of Ti O₂ improved the light barrier properties of the film and the CS-0.6 film had the lowest CEO loss rate under UV light,which extended the shelf life of the fruit.The antioxidant and antibacterial properties of the films increased with increasing concentrations of CEO.The water vapor permeability（WVP）of the CS-0.6 bilayer film was the lowest[4.21 x 10-8 g/（m-s-Pa）],26.7%lower than that of the blank film（CS-0 film）,which effectively slowed down the water loss from the fruit.Experimental results showed that the CS-0.6 bilayer had the best overall performance.（2）Preparation and characterization of CH-CD and C-C/S-T composite films loaded with Pickering emulsionsThe Pickering emulsion system was constructed to address the problems of high volatility and poor compatibility of the CEO.The oil-in-water Pickering emulsionγ-CD-CEO was successfully prepared using CEO as the oil phase and food-gradeγ-cyclodextrin（γ-CD）as the solid particle stabilizer.The successful preparation of the oil-in-water emulsion system was confirmed by Confocal laser scanning microscope（CLSM）.Pickering emulsion films were prepared by incorporating emulsions into chitosan matrices.The experimental results showed that the incorporation of emulsions improved the antioxidant and antibacterial properties of the single CH films.SEM showed that the CH-CD II film had a tight,dense cross-section,suggesting that the Pickering emulsion system improved the poor compatibility of the CEO with the CH matrix,which resulted in optimal mechanical properties and the lowest WVP of the film.At the same time,the Pickering emulsion system reduced the CEO loss rate of the CH-CD II film,which contributed to a longer shelf life of mangoes.The overall performance of the CH-CD II film was the best by comparative analysis.A bilayer UV-resistant Pickering emulsion film was constructed on the basis of CH-CDⅡfilm by layer self-assembly method.The C-C/S-T bilayer was successfully prepared by using SA containing Ti O₂ as the outer layer and CH containingγ-CD-CEO Pickering emulsion as the inner layer.The films were compared with the CS-0.6 and CH-CDⅡfilms selected from previous experiments,and the performance differences between the three films were analyzed comprehensively.SEM showed that all three films had dense cross-sections.The C-C/S-T film had the highest elongation at break（EB）（29.57%）and better blocking ability for UV and visible light.During UV irradiation,the C-C/S-T film showed the lowest loss rate of CEO and the slowest decrease in oxidation resistance and antibacterial ability.The results indicated that the C-C/S-T bilayer film possessed optimal overall performance and could be used for subsequent studies.（3）Study on the effect of electrostatic spraying on the quality of coating film and mango preservationIn order to enhance the coating transfer efficiency and improve the coating quality,this study used electrostatic spraying method for mango film preservation experiments.The effect of the electrostatic spraying method on the quality of the coating film and the freshness of the mangoes was analyzed comprehensively by comparing it with dip coating,brush coating and spraying methods.Microscopic（SEM,AFM and fluorescence microscopy）and macroscopic（water-sensitive paper experiments）results showed that the film layer formed by the electrostatic spraying method had a uniform,smooth and continuous surface.In addition,the electrostatic spraying method had the highest film transfer efficiency and the shortest film drying time,which reduced the waste of coating solution and energy consumption and lowered production costs.The analysis of mango preservation indicators showed that the weight loss,hardness,total soluble solids,malondialdehyde and total phenolic content of mangoes after electrostatic spraying treatment were significantly improved compared to the control group.No large dark brown areas or black spots appeared on the epidermis of the electrostatic sprayed mangoes.Therefore,the electrostatic spraying method can improve the quality and transfer efficiency of the coating film and improve the freshness of mangoes,which is an efficient and feasible new coating method.