| One of the biggest functions of food packaging is to ensure the hygiene of food,avoid damage and contamination during handling,transportation and storage,and extend the shelf life of food.Plastic food packaging waste has caused serious environmental pollution,which has affected the advancement of carbon peak and carbon neutral goals.At present,the development of environmentally friendly natural biomacromolecule degradable film materials to replace plastic packaging films in food packaging has become a research hotspot in the field of food packaging.Chitosan has the advantages of abundant sources,biodegradability and antibacterial properties,and the chitosan packaging film made of it is widely used in the fields of food and medical materials.However,due to the structural limitations of natural polymers,the thermal stability,mechanical properties and barrier properties of a single chitosan film material are poor,and its effect on food preservation is limited,which greatly limits its application as a packaging material in the food industry.At present,the methods applied to the modification of natural macromolecular membranes include chemical modification,physical modification and composite modification of nanoparticles.Due to the smaller size and larger specific surface area of nanoparticles,the structure of the composite modified film can be denser,and the mechanical strength and barrier properties can be improved.For this reason,this study uses chitosan as the filmforming matrix to develop a microporous plastic wrap material containing nanoparticles.Firstly,polyphenol(tannic acid)zein nanoparticles were prepared,and the effects of nanoparticles on the mechanical properties,air permeability and antioxidation properties of chitosan-based films were studied.The application effect of the chitosan composite film in the preservation of sugar oranges.The main research contents and results are as follows:(1)Zein-tannic acid(TA)nanoparticles(ZTNPs)were prepared by anti-solvent precipitation method,and their structure and properties were characterized.It was found that the sizes of nanoparticles prepared under different p H conditions were different,but the particle sizes were all less than 200 nm.Compared with the particles prepared at p H 2 and p H 4,the particle size of ZTNPs at p H 7 was relatively larger,with the largest particle size of 190.53 nm(at a zein/TA ratio of 1:1).The main force for the formation of ZTNPs was the hydrogen bond and hydrophobic force formed between the amide group of zein and the hydroxyl group of tannic acid.The addition of tannic acid caused changes in the secondary structure and self-assembly behavior of zein,forming a complex colloidal structure.The evaluation of antioxidant activity showed that the addition of tannic acid significantly enhanced the antioxidant capacity of ZTNPs.When the concentration of tannic acid was greater than 10 mg/m L,the PTIO free radical scavenging rate of ZTNPs was greater than 50%,and the total antioxidant capacity was greater than 600 U /mL.(2)Zein-tannic acid nanoparticles/chitosan composite film was prepared by casting method.Scanning electron microscope results showed that after adding nanoparticles,the surface of chitosan composite film became rough,but the overall structure became more compact.Both ZTNPs and chitosan matrix had good biocompatibility.Further structural analysis found that ZTNPs interacted with chitosan matrix during the complex process,such as hydrogen bonds and electrostatic forces.The properties of the composite membrane were evaluated,and the results showed that the mechanical strength of the composite membrane was enhanced,the tensile strength increased from 13.44 MPa to 39.86 MPa,the elongation at break increased from14.37% to 37.56%,and the water vapor and oxygen transmission coefficients of the composite film were respectively Reduced by 70.76% and 40.68%,DPPH and PTIO free radical scavenging rate reached 88.07% and 33.66%,respectively.(3)The effect of ZTNPs/chitosan film-forming solution on the fresh-keeping effect of sugar oranges coating treatment was studied.The results showed that the ZTNPs/chitosan coating reduced the weight loss rate of tangerines,and the weight loss rates of tangerines stored at 10 ℃ and 25 ℃ decreased by 34.92 % and 46.16 %,respectively.The ZTNPs/chitosan coating reduced the nutrient loss rate of sugar oranges,which mainly showed that the nutrients of sugar oranges were decomposed and consumed during storage.The retention rate of titratable acid content was as high as 78.65%;the content of vitamin C,total phenols and flavonoids increased by 21.16%,42.34% and 24.94% respectively compared with the blank control group(25 ℃).In addition,the total sugar and soluble solids content remained at a relatively high level at the end of storage,which were 98.55 g/L(10 ℃)and 12.50%(25 ℃),respectively.The nanoparticle composite film effectively slowed down the loss of fruit nutrients.The above research results show that the ZTNPs/chitosan composite film has the potential to be developed as a new packaging material for fruit preservation. |
