Protein edible films are mainly made of animal protein isolates and plant protein isolates, such as whey protein, gluten and zein.
In the process of film formation, the protein film mainly relies on the action of disulfide bonds (S-S), which is firstly cleaved into sulfhydryl groups through the reduction of S-S bonds, and diffused in the solvent to reduce the polypeptide molecules, and then the diffused protein molecules It is oxidized again in the air, and the S-S bond is re-formed to form a thin film structure. Common protein edible films mainly include soybean protein isolate film, whey protein film, wheat gluten protein film and zein film.
1. Soy protein isolate film The film uses soybean protein isolate as the main raw material, adds glycerin, and makes edible film under two acidic and alkaline conditions, respectively. Soy protein isolate membrane has good mechanical properties and moisture resistance. Deng Yangwu et al. studied the film-forming properties of soybean protein isolate and concluded that under the conditions that the ratio of soybean protein isolate and glycerol was 2.5:1, the pH value of the film solution was 7, and the film preparation temperature was 90 °C, the film can be prepared. Edible packaging cling film with good tensile strength and elongation is obtained.
2. Wheat gluten film Wheat gluten is mainly composed of glutenin and gliadin, of which the content of glutenin accounts for 30%-40%, and the content of gliadin accounts for 40%-50%. Due to the elasticity of glutenin and the extensibility of glutenin, it can form a network structure with water, so it has unique physical properties such as excellent viscoelasticity, extensibility, water absorption, liposuction and emulsification, and film-forming properties. Luli Meng et al. studied the effect of lipids on the mechanical properties and permeability of wheat protein membranes. The results showed that due to the hydrophobic properties of lipids, which can effectively prevent moisture migration, complexing them with proteins can improve the moisture barrier properties of protein membranes. In addition, the mechanical properties and water solubility of wheat protein membranes also vary with the type and amount of lipids.
3. Zein Membrane Zein has good hydrophobic properties that other protein films do not have, and is easy to form a film. It forms a random coil structure in an alcohol-water solution. After evaporation of the solvent, it can be made into a transparent and glossy film with moisture-proof, Oxygen barrier, anti-ultraviolet, fragrance preservation, oil resistance and anti-static properties, and have a certain inhibitory effect on bacteria, can extend the shelf life of food. Yan Jingkun et al. showed that with the increase of refrigeration and freezing time, the tensile strength and elongation of protein membrane decreased; under refrigeration conditions, the mechanical properties of protein membranes were better than those under freezing conditions;
4. Peanut Protein Isolate Film Peanut protein isolate has good film-forming properties. Peanut protein isolate film has a certain tensile strength, and also has a certain ability to prevent the migration of water vapor, is a promising edible film. Jangchud studied the effects of glycerol, sorbitol, polyethylene glycol, and propylene glycol on peanut protein films. The results show that glycerol has the best effect as a plasticizer. When the mass ratio of glycerol to protein is 0.67~1.67g/g, it does not affect the water permeability and oxygen permeability, but can significantly improve the elongation at break.
5. Silk Fibroin Membrane Xie Ruijuan and Li Mingzhong used epoxy resin as cross-linking agent to prepare sericin film with certain mechanical properties, so that its physical properties were well improved. Both the tensile strength at break and the elongation at break are relatively good. Chen Jianyong et al. prepared nano-TiO2 modified regenerated silk fibroin membrane by sol-gel method. The mechanical strength of the silk fibroin film was improved, and the dissolution rate in water was decreased.
6. Sunflower Protein Film Orliac studied the effects of glycerol, ethylene glycol, diethylene glycol, triethylene glycol, and propylene glycol on the properties of hot-molded sunflower protein films, and pointed out that triethylene glycol and glycerol were the most suitable plasticizers for sunflower protein.
7. Myogenin Membrane The Natick Institute of the United States uses an edible packaging film made of animal protein collagen to package meat, which is characterized by high strength, water resistance and good water vapor barrier properties. It can also be eaten and is harmless to the human body. At the same time, it also solves the problem of ocean pollution caused by food packaging plastics.
