| Food safety is a widely concerned livelihood issue.Food spoilage or invalid shelf life printed on food packaging can lead to disease and waste of resources,for which smart packaging was born.Smart food packaging is a new technology that monitors the quality and safety of food throughout its shelf life.This approach embeds sensors and indicators into the packaging to monitor changes in the physiological properties of food.Smart packaging substrates mostly use natural and environmentally friendly biodegradable materials,among which chitosan,as a natural bio-based polymer with excellent biocompatibility,non-toxicity and film-forming properties,is considered an effective alternative to traditional petroleum-based packaging,however,its antibacterial properties are limited and its light barrier properties are weak,and it needs to be mixed with other excellent materials to improve its applicability.Anthocyanins,as a pure natural water-soluble pigment with certain p H sensitivity,antioxidant and antibacterial properties,have great potential for application in intelligent food packaging.Zn O nanoparticles,which not only have certain antibacterial properties but also can be blended with substrates to produce nano-effect,are widely used in the blending modification of polymeric materials.In this study,anthocyanins extracted from purple tomatoes and zinc oxide nanoparticles were blended with chitosan film substrates to improve the mechanical properties,barrier properties and antibacterial properties of chitosan,so as to prepare smart packaging films with good overall performance,and the main research contents are:(1)CS/PTA composite films with PTA mass fractions of 0%,1%,3% and 5%(PTA relative to CS percentage)were prepared by solution blending method using chitosan(CS)as substrate and purple tomato anthocyanin(PTA)as additive.The effects of PTA concentration on contact angle,tensile strength and water vapor transmission rate of the composite membranes were investigated,and the p H sensitivity of the composite membranes was examined by their color response to different p H values.It was found that PTA showed purplish-red color in acidic environment,lavender transparent and close to colorless transparent in neutral environment,and orange-yellow in alkaline environment.the addition of PTA reduced the hydrophilicity of CS/PTA composite film,while the tensile strength and elongation at break of the composite film increased significantly.The color change of the CS/PTA composite film with high concentration was less obvious under acidic conditions,and the color of the composite film obviously became yellow under alkaline conditions.the change of PTA on p H was more obvious,but the color change of the film was less obvious after mixing with chitosan matrix,which might be due to the chemical reaction between chitosan and purple tomato anthocyanin after mixing,which degraded the purple tomato anthocyanin and led to the poor color change.(2)CS/PTA/ZP films were prepared by mixing chitosan(CS)and zinc oxide nanoparticles(ZP)with purple tomato anthocyanin(PTA).The effects of different Zn O nanoparticles on the properties of film p H color response,UV-Vis transmission spectra,thickness,moisture content,water contact angle,mechanical properties,microscopic morphology,Fourier transform infrared spectra,antioxidant and antibacterial activities were investigated.By comparing the experimental results of composite films of chitosan matrix after the addition of purple tomato anthocyanin and zinc oxide nanoparticles,it was found that the doped zinc oxide nanoparticles enhanced the compatibility of PTA with CS.The tensile strength,antioxidant and antibacterial properties of CS films were significantly enhanced by Zn O nanoparticles and PTA with increasing Zn O nanoparticles content,while the elongation at break of the composite films decreased.(3)The application of CS/PTA and CS/PTA/ZP films on pork packaging was examined.It was found that the color of CS/PTA and CS/PTA/ZP films changed from dark green to brown as the spoilage of pork increased,thus,given the antioxidant,antibacterial,and freshness indicating properties of said prepared CS/PTA and CS/PTA/ZP films for pork,the films are expected to be applied to future food active packaging and smart packaging. |
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