| Innovations in food packaging systems can help meet the changing needs of the market,such as reducing the negative environmental impact of food packaging and consumer preferences for healthy and high-quality food.Current advanced food packaging reduces the negative environmental impact of food packaging through the use of edible or biodegradable materials,plant extracts and nanomaterials,and gives packaging materials functions such as freshness monitoring and preservation.The development of advanced food packaging materials is currently divided into two main directions,one of which is the development of green and safe sustainable packaging to mitigate environmental pollution caused by petroleum-based packaging,and the other is the development of functional packaging such as active packaging and smart packaging,which have been developed to provide many innovative solutions.At the same time,sustainable packaging technologies and functional packaging technologies can work in synergy for the preparation of sustainable and functional food packaging,which has become a hot research topic in the field of advanced packaging materials.Purple corn cob is a common agricultural waste that is often burned,buried or used as animal feed.In this paper,smart packaging with freshness monitoring function and photothermal packaging with sterilisation function were prepared from purple corn cobs,from which anthocyanins were extracted,and chitosan,a sustainable material,was used as the substrate,respectively.The main research contents and results are as follows:(1)Anthocyanins was extracted from purple corn cobs by ultrasound-assisted method.The effects of sonication time,ethanol volume fraction and material-to-liquid ratio on the total anthocyanin content in purple corn cob extract were investigated separately,and the extraction process of anthocyanins was optimised using a Box-Behnken design experimental scheme based on the results of single-factor tests.In addition,the anthocyanin species and their contents,p H-responsive properties and optical properties of purple corn cob extract(PCCE)were also investigated.The optimum extraction parameters of the anthocyanins from purple corn cobs were 1:17.09,47.72% volume fraction of ethanol and 15.64 min of sonication time,and the total anthocyanin content of 27.6 mg/g.The color of purple corn cob anthocyanins changed significantly in different p H buffers,showing a red color at p H < 6,a blue-purple color at p H 6 to 9 and a yellow color when p H > 10.It is evident from the full wavelength UV results that the structure of purple corn cob anthocyanins also changes somewhat when the p H is changed,showing the inherent properties of anthocyanins.(2)Using the p H-responsive properties of purple corn cob anthocyanins,a smart package with freshness monitoring function was constructed and its application in the freshness monitoring of meat products was explored.In order to be able to make full use of purple corn cobs,lignin-containing cellulose nanocrystals(LCNC)was extracted and the properties were explored.LCNC-chitosan-purple corn cob extract(LCNC-CS-PCCE)composite films with p H-responsive properties were constructed using chitosan(CS)as the matrix and purple corn cob extract as the active ingredient.LCNC was added to enhance the mechanical properties.The prepared composite films were applied to the freshness monitoring of fresh shrimp and pork,and the basic properties of the membranes were characterised.The results showed that PCCE imparted sensitive and stable p H responsiveness to the films,while the addition of LCNC not only enhanced the mechanical properties of the films,but also increased the UVbarrier and hydrophobicity of the films.The results of the freshness monitoring experiments on pork and fresh shrimp showed that the p H and TVBN of the meat increased with the increase of storage time,and the shrimp and pork started to deteriorate on day 2 and day 4respectively,while the colorimetric test results of the film showed a significant color change of the film,with the film changing from yellow to grey,indicating that the LCNC-CS-PCCE composite film has good freshness monitoring capability.(3)Based on the photothermal conversion ability of anthocyanin and iron ion complex(PCCE/Fe),they were used to prepare antibacterial films with photothermal effect.PCCE/Fe complex was prepared by mixing purple corn cob anthocyanins with iron ions,and the microstructure and photothermal conversion properties of the complex was characterized.Using chitosan as a matrix,chitosan solution was mixed with PCCE/Fe complex to prepare purple corn cob extract/iron ion-chitosan(PCCE/Fe-CS)complex films and characterize the basal and photothermal bactericidal properties of the complex.Using cherry tomato as a model,the effect of photothermal sterilization film on the preservation of cherry tomato was investigated.The microstructure of the complex and the results of the photothermal conversion performance showed that the PCCE/Fe complex exhibit a homogeneous spherical shape and have good photothermal conversion performance.Characterization results of the photothermal film showed that the photothermal sterilisation film had good photothermal conversion performance and sterilisation ability.In application tests,cherry tomato wrapped with the photothermal composite film showed less change in p H,hardness,and weight loss before and after storage compared to bare fruits,indicating that the PCCE/Fe-CS composite film has better fruit preservation function than CS film and polyethylene film.In this study,purple corn cobs were used as the basis from which purple corn cob anthocyanins were extracted.The sustainable smart packaging and sterilised packaging were prepared respectively based on purple corn cob anthocyanins,both of which were found to have good performance after characterization and application.The advanced food packaging based on purple corn cobs provides a new research idea for the development of inexpensive and sustainable functional food packaging materials. |
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