| Food freshness indicator film is a smart packaging material that achieves monitoring of food freshness through color change.Anthocyanins have antioxidant and antibacterial properties as well as being a gas-sensitive material that can identify spoilage odor of meat foods.Therefore,we can prepare multifunctional packaging films with the help of anthocyanins,which can ensure the freshness of food and also effectively prevent oxidation and bacterial growth.Currently,anthocyanins have been extensively studied in the field of food packaging.However,in practical applications,anthocyanins are not only sensitive to p H value due to their unique structure,but also easily disturbed by external environment.To overcome these drawbacks,a variety of novel antimicrobial functional additives have been investigated to inhibit or kill microorganisms,and the most common method is to add them to food products.ε-polylysine,a biological metabolite of natural origin,possesses excellent bactericidal ability and thermal stability,and is a biological preservative with excellent preservative properties and broad commercial prospects.In this project,CS/TA/ε-PL composite film was prepared by flow-delaying method using chitosan(CS)as matrix material,tomato anthocyanin(TA)as p H indicator and ε-polylysine(ε-PL)as bacteriostatic agent,and the effect of ε-polylysine content on the physical and chemical properties and color stability of CS/TA/ε-PL composite film was investigated,and finally the film was applied to fresh pork to examine its The film was finally applied to fresh pork to investigate its freshness preservation and freshness indication performance.The main research contents are as follows:First,the preparation process of smart packaging film and its performance study.CS/TA/ε-PL composite films with different concentrations of ε-polylysine(0%,1%,3%,5%,7%)were prepared by flow casting method and characterized for water content,swelling index,mechanical properties,moisture permeability,oxidation resistance and bacterial inhibition,as well as infrared spectral analysis.The results revealed that the addition of ε-PL significantly improved the mechanical properties,swelling index and barrier properties,and antioxidant properties,while there was no significant effect on the water content of the membranes.Infrared spectroscopy analysis revealed that tomato anthocyanins and ε-PL were well dispersed in the film-forming matrix,and a large number of hydroxyl groups in the pigments formed hydrogen bonding interactions with the film-forming matrix.The addition of ε-PL significantly enhanced the inhibitory efficacy of the films against E.coli and S.aureus.Compared with E.coli,the CS/TA/ε-PL composite film showed more significant effect in the inhibition of S.aureus.Secondly,study of p H sensitivity and color stability of smart packaging films.A colorimeter was used to compare the responsiveness of tomato anthocyanins to p H and to study the effect of different levels of ε-PL on the color stability of the films under accelerated conditions such as light and high temperature.It was found that in the range of p H 2-12,with the change of tomato anthocyanin structure,the color change of the solution was from purplish red → colorless → light blue → yellow in order,while the absorbance and wavelength also kept changing with it;in light,high temperature and p H,the stability of anthocyanin in its film was improved by ε-PL,and the preservation rate was significantly increased,in addition to the change of color difference value results also indicated that the color development stability of the filmFinally,study on the preservation and freshness detection of pork by smart packaging films.Pork was packaged using the film in a simulated supermarket storage at 4°C and its freshness preservation was evaluated by measuring the sensory evaluation,p H,TVC and TVB-N during storage.In addition,the color change of the composite films in pork samples was measured with time.UV spectrophotometry was used to measure the changes in the values of each index over different time periods.The experimental results showed that compared to the blank group,the pork in the experimental group showed slow changes in p H,microbial content and TVB-N content during storage,as well as a slowdown in spoilage rate.Especially,ε-PL/7% had the most significant effect on pork preservation,and the composite film had the strongest color development,the largest change and the easiest identification.In conclusion,ε-PL can improve the stability of tomato anthocyanins,and the best results in terms of mechanical properties,water content,antioxidant and antibacterial properties of the film were obtained at a concentration of 7%.The film has certain freshness preservation for fresh pork and the freshness of pork can be monitored by color change,so the film has good application prospects in the field of intelligent food packaging and active packaging. |
PDF Full Text Request