Frozen food is very susceptible to deterioration due to external environmental factors during storage and transportation. The barrier properties of automatic packaging film for frozen food are the key to ensuring food quality. By effectively blocking substances such as moisture, oxygen, and odor, packaging film can delay physical, chemical, and microbiological changes in food, maintain the taste, nutrition, and safety of food, and play an irreplaceable role in extending the shelf life of frozen food and enhancing product value.
Moisture barrier is the basic line of defense for frozen food preservation. In a frozen environment, the moisture in food will undergo "sublimation-condensation" due to temperature fluctuations, causing food to dehydrate and shrink, and quality deterioration. The packaging film achieves moisture barrier by virtue of its low permeability to water vapor. The principle is to select high-barrier materials, such as ethylene-vinyl alcohol copolymer (EVOH) and polyvinylidene chloride (PVDC). These materials have a tight molecular structure and are difficult for water molecules to penetrate. They can prevent the loss of moisture inside the food and the intrusion of external moisture, keep the moisture content of the food stable, and avoid problems such as poor taste and weight loss caused by moisture migration.
Oxygen barrier is the core element to ensure the quality of frozen food. The presence of oxygen will accelerate the oxidation and rancidity of fats and fats, the degradation of vitamins and the reproduction of microorganisms in food. The oxygen barrier effect of packaging film is based on physical obstruction and chemical adsorption. On the physical level, the dense film material structure forms a gas molecule diffusion barrier; on the chemical level, the residual oxygen in the package is actively absorbed by adding oxygen absorbers. For example, in composite packaging films containing nanoclay, the nanoclay flakes form a tortuous diffusion path in the film, reducing the oxygen permeability; packaging films containing iron powder oxygen absorbers react chemically with oxygen to reduce the oxygen concentration to an extremely low level, thereby inhibiting food oxidation and microbial growth, and maintaining food color, flavor and nutrition.
Odor barrier is also indispensable for the preservation of frozen food. Frozen food will produce volatile odors during storage, and it is easy to absorb external odors, affecting quality. Packaging films protect against odors by blocking volatile organic compounds (VOCs). Some packaging films add adsorbent materials such as activated carbon and use their porous structure to adsorb odor molecules; some film materials rely on low surface energy and chemical inertness to prevent odor molecules from penetrating and diffusing. In addition, multi-layer composite packaging structures can also improve the odor barrier effect. The functional layers work together to isolate food from the odor environment and retain the original flavor of the food.
The barrier properties of packaging films are closely related to their thickness, structure and processing technology. Generally, increasing the film thickness can improve the barrier properties, but it will increase costs and reduce flexibility. Multi-layer composite structures have become the optimal choice, combining high-strength wear-resistant materials on the outer layer, high-barrier materials in the middle, and heat-sealed materials on the inner layer, which not only ensures comprehensive performance but also enhances the barrier effect. Advanced processing technologies such as blow molding, cast film, coating, etc. can control the microstructure of the film and reduce internal defects. The biaxial stretching process can directionalize the film molecules and enhance the density and barrier properties.
In order to further improve the barrier properties of automatic packaging film for frozen food, new materials and technologies are constantly emerging. The application of nanomaterials has attracted much attention. Evenly dispersing nanoparticles in the packaging film matrix can form a nano-level barrier, which significantly enhances the barrier capacity for gas and moisture. Smart packaging technology also brings new directions for preservation. Smart indicators can monitor the gas composition, temperature, humidity and other parameters in the package in real time. Once the food shows signs of deterioration, it will send a signal in time to provide decision-making basis for consumers and enterprises.
As consumers' requirements for food quality and environmental protection increase, the barrier property research of automatic packaging film for frozen food will develop in the direction of green, environmental protection and intelligence. Research and development of degradable high-barrier materials to reduce the pollution of packaging waste to the environment; combined with Internet of Things technology, the information interaction between packaging film and food supply chain will become an important trend in the future frozen food packaging field, providing more efficient and sustainable solutions for food preservation.
