Study On Preparation And Properties Of Intelligent Food Packaging Films Based On Freshness Colorimetry Sensing

Intelligent food packaging is based on sensing the physical,chemical and biological changes of the food inside or around the food,monitoring and recording food itself and the environmental changes inside and outside the package,communicate with consumers on the real-time status of packaged food.Due to the growth of microorganisms in food packaging and biochemical changes of food ingredients lead to p H changes in the environment around food,p H changes often represent food spoilage,and the natural pigment of plant has the biological activity which displays the different color change under the different p H value,on this basis,the intelligent food packaging based on the freshness colorimetric sensor based on p H-sensitive pigment which extracted from plant has been widely studied.The intelligent food packaging based on colorimetric sensor can display the freshness of the packaged food through the change of color of packaging film,then achieving the goal of communication with consumers.In this study,intelligent food packaging films were prepared based on litchi shell extract(LE)and mangosteen shell extract(Mse),the pigment in LE and Mse were p H sensitive materials,the structure and properties of p H sensitive materials and films were characterized.The main contents can be divided into the following two parts:(1)The characterizations of extracted anthocyanins in litchi shell extract and study on gelatinbased freshness colorimetric sensing intelligent food packaging films.Small pieces of dried litchi shell was soaked in ethanol solution to extract.The contents of anthocyanins in the extracts of litchi shell was determined by p H differential method after extracts was diluted by the rotary evaporating solution.A variety of color changes were found in the anthocyanidins in litchi shell extract when the extract was diluted with p H = 2-12 buffer solution,it was suitable to be used as a p H sensitive material in the intelligent food packaging film based on the freshness colorimetric sensor,and the UV-Vis absorption spectrum of the rotation evaporation extract solution was conducted,and the structure changes of anthocyanins in the extract at different p H values were studied.The anthocyanin extracted from litchi shell was used as a p H color indicator,intelligent food packaging films based on the freshness colorimetric sensor with single-component Gel/LE,double-component Gel/Csa/LE and triple-component Gel/Csa/PVA/LE films were prepared by solution casting method,the mechanical properties,optical properties,antibacterial and antioxidant activities of films were studied and characterized.It was found that no new chemical bonds were formed between the components of films,and the addition of litchi shell extract did not affect the crystallization of films.The films with LE were rougher,denser and more uniform than those of the films without LE in the SEM.In the ultraviolet region,the Gel/Csa/LE and Gel/Csa/PVA/LE films with LE have better ultraviolet light barrier,and their transmittance were only 0-7% and 0-13%,respectively.In addition,the Gel/Csa/PVA/LE films have higher visible light transmittance in the visible region.After adding LE,the moisture content and water vapor barrier of Gel/Csa/PVA/LE films decreased by 10% compared with Gel/Csa/PVA films,and Gel/Csa/LE films decreased by 5%compared with Gel/Csa/LE films,Gel/LE film was 14% lower than Gel film,but the antioxidant performance of Gel/Csa/PVA/LE film was improved by 7% than Gel/Csa/PVA film,Gel/Csa/LE film was improved by 15% than Gel/Csa film and Gel/LE film was improved by10% than Gel film.The antibacterial activity of three films with LE was almost 100%.The mechanical properties of Gel/Csa/PVA/LE films(18.60 MPa,116.00% EB)were also superior to Gel/LE(9.45 MPa,61.14% EB)and Gel/Csa/LE(8.14 MPa,64.00% EB)films.The Gel/Csa/PVA/LE films can quickly show visible color change at 25 °C and 4 °C.To sum up,the Gel/Csa/PVA/LE films have excellent mechanical properties,antibacterial and antioxidant activity,so the film can be used as intelligent food packaging film with the freshness colorimetric sensor to extend the shelf life of food.(2)The characterizations of extracted anthocyanins in mangosteen shell extract and study on CMC-based freshness colorimetric sensing intelligent food packaging films.In order to search for better p H-sensitive materials,Mse was used as p H indicator,soaked small pieces of dried mangosteen shell in ethanol solution,then evaporated,diluted and determined the content of anthocyanin in Mse by p H differential method.The extract was diluted with a certain p H = 2-12 buffer solution,and the color changes were recorded by taking photographs,the structure of anthocyanin in the extract was studied by UV-Vis absorption spectrum analysis under different p H values.To avoid the complexity of the preparation process of triple-component matrix films,waste materials,the intelligent food packaging films based on double-component matrix CMC with freshness colorimetric sensor were prepared by solution casting method,the mechanical properties,optical properties,antibacterial and antioxidant activities of the films were studied and characterized.It was found that no new chemical bonds were formed between the components of films,and the addition of Mse did not affect the crystallization and thermal stability of the films.For the optical and mechanical properties,the films with Mse had better UV light barrier and mechanical properties.The transmittance of CMC/Agar/Mse films in the UV region was 0-55%,CMC/Cst/Mse was 0-30%,and CMC/Agm/Mse was 0-26%.The CMC/Cst/Mse films have better mechanical properties(20.62 MPa,4.04% EB),lower moisture content(1.60%),lowest water vapor permeability,and the free radical scavenging ability of the Mse-containing films was double than that of the Mse-free films,CMC/Cst/Mse film had the best results(40%),and CMC/Cst/Mse film also had the best antibacterial ability.The CMC/Cst/Mse film could show visible color change at 25 °C in fish freshness monitoring.In a word,the CMC/Cst/Mse film can be used as intelligent food packaging film for freshness colorimetric sensing to extend the shelf life of food.