Preparation And Properties Of Carvacrol Nanoemulsion-carboxymethyl Chitosan Composite Food Packaging Film

With the improvement of people's living standard,food safety has been paid more and more attention by the society.At present,the addition of chemical preservatives and the use of plastic packaging materials are still common methods to avoid food contamination and extend the shelf life of food.However,many processed foods are used frequently,and the abuse of chemical preservatives has a serious negative impact on human health.Besides,plastic packaging is difficult to degrade,resulting in a large amount of plastic waste in the environment.In order to solve these problems,this research designs and uses plant bacteriostatic agents and chitosan derivatives to prepare composite food packaging film that can inhibit bacteria,remove free radicals effectively and biodegrade.The main research contents are as follows:1.Use carvacrol essential oil,a plant active ingredient,as an antibacterial agent and prepare its nano emulsion.The traditional spontaneous emulsification method is improved,the carrier oil is discarded,and carvacrol is taken as an oil phase to directly prepare stable oil-in-water carvacrol nano emulsion?CA-NEs?.This strategy can greatly increase the content of active substances in the emulsion,effectively avoid the influence of the carrier oil on the physical and chemical properties of the active ingredients,and reduce the energy consumption and instrument cost in the preparation process.The effects of surfactant type,oil phase/surfactant ratio,concentration,emulsification method and other conditions on the formation and stability of CA-NEs were studied in detail.The reaction conditions were optimized and nano-emulsion with particle size less than 200 nm was obtained.The concentration of carvacrol in the preparation could reach up to 5%.The size,charging property,microscopic morphology,surface tension,viscosity and other properties of CA-NEs were characterized.Based on this,the formation mechanism of CA-NEs in self-emulsification process was analyzed.On this basis,the function of CA-NEs is analyzed in detail:the physical stability experiment results show that the system can maintain nano-emulsion state for a long time in a wide pH range and under high ionic strength.Microbiological test results showed that CA-NEs had better antibacterial activity than pure carvacrol.Spectroscopic results showed that the DPPH scavenging rate of CA-NEs was as high as 53.7%.The expanded research results show that CA-NEs has excellent water dispersibility and can be freely spread on the surfaces of plant leaves such as wheat,rape,persimmon,etc.In theory,CA-NEs can be used as a plant-derived pesticide in the prevention and control of crop pathogenic bacteria.2.Using biological macromolecule carboxymethyl chitosan?CMC?as raw material,food packaging film was prepared.Firstly,a small amount of CMC molecules in the solution are aggregated by using a solvent exchange method through dehydration of ethanol,and chain entanglement,hydrogen bonds and hydrophobic-hydrophobic force are induced among molecules to obtain self-crosslinking CMC microgel;The physical and chemical properties of microgel,such as size,electrical property,micro-morphology,viscosity,surface tension,etc.,were studied,and its formation mechanism was explained.Then,CMC membrane was efficiently prepared by electrostatic spraying method based on the low surface tension of microgel system.Furthermore,Ca²⁺was introduced into the membrane based on the principle that high valence metal ions are easy to form coordination bonds and ionic bonds with polymer oxygen-containing groups and carboxylic acid groups to further crosslink polymer chains inside the membrane,thus greatly improving the physical stability of the membrane.The water immersion loss rate was reduced from 82.6%to 3.8%.Finally,CA-NEs was loaded by the swelling effect of the film to obtain the carvacrol nanoemulsion-carboxymethyl chitosan composite food packaging film-CA-NES@CMC with antibacterial and free radical scavenging functions.In this paper,the properties and functions of CA-NEs@CMC are analyzed in detail by a variety of experimental methods.Electron microscope results show that the thickness of CA-NEs@CMC film gradually decreases with the increase of CA-NEs content due to osmotic pressure.Spectroscopic results showed that the content of carvacrol in CA-NEs@CMC membrane was as high as 26.96 mg g-1 and DPPH scavenging rate was as high as 53.7%.Microbiological test results showed that CA-NEs@CMC membrane had good antibacterial activity against Gram-positive bacteria?Staphylococcus aureus?and negative bacteria?Escherichia coli?,with the highest inhibition rates of 99.9%and 99.0%respectively.The practical application results show that CA-NEs@CMC can protect wheat bread from bacterial contamination under non-contact conditions,and the shelf life increases with the increase of carvacrol concentration in the film,reaching a maximum of 7days.In summary,the carvacrol nanoemulsion-carboxymethyl chitosan composite food packaging film designed and prepared by the author has good antibacterial and free radical scavenging functions,and can protect food safety under non-contact conditions.The methods and principles involved in this paper will promote the development of surface interface,colloid chemistry and polymer science,and will also lay a theoretical and practical foundation for the wide application of plant-derived nanomaterials and preparation technology in production and life.