Research And Preparation Of Intelligent Packaging For Fish Freshness Detection Based On Red Dragon Fruit Pigment

The red dragon fruit is a kind of nutritious food and the purple of flesh is due to the existence of betacyanin,which is a kind of water-soluble pyridine derivatives with abilities of antioxidant,antibacterial and scavenging free radicals.In food applications,betacyanin is usually considered as a functional and natural colorant.when added to the food,it not only increase the beauty of foods,but also increases the antioxidant activity of the food.Our focus is on the use betacyanin as a natural pH indicator.Mixed with carboxymethyl cellulose and glycerin,it can be made into a thin film,used to monitor the freshness of fish.The betacyanin can sensitively response volatile dimethylamine in a colorimetric way,while the volatile amines are potential indexes for freshness of fish.At first,the red dragon fruit is squeezed into juice.Then filter it,take the supernatant and make it into freeze drying powder to get the freeze-dried powder of red dragon fruit flesh extracts(FPRE).Add FPRE in the mixture of carboxymethyl cellulose(CMC)and glycerin to prepare films by solvent evaporation method and manufacture FFS FPRE10/25/50/100 films.The mechanical properties of different films show that with the increase of FPRE content,the tensile strength of film gradually reduced,while elongation at break and the thickness increased.For film thermal stability,the more FPRE added,the higher the thermal stability of film is.The film surface SEM observed proved that FPRE content in film has no effect on the microstructure of its surface.All films showed smooth and uniform surface texture.FT-IR spectra confirmed that added FPRE is indeed immobilized in carboxymethyl cellulose/glycerol matrix.When the pH changed from 1 to 13,FPRE aqueous solution responsed in a colorimetric way and the color is from red to yellow.In addition,the film also showd response to dimethylamine gas.The film color changed from red to brown,and finally yellow.The UV-vis spectra also changed accordingly.Fish freshness detection experiment showed that the FFS-FPRE10 film demonstrated the highest color variation rate and the greatest color change during the 11 days of refrigerated storage of fish.Therefore,FFS-FPRE10 film was used for intelligent packaging preparation.This packaging system is convenient for consumers to determine fish freshness degree and whether it is still edible.And the results were confirmed by the traditional detection method.Therefore,the intelligent packaging can be regarded as an effective means of monitoring fish freshness.