Frozen food refers to food with qualified quality food raw materials that have been properly processed, frozen at a temperature of -30°C, and then stored and circulated at -18°C or lower after packaging. Due to the use of low-temperature cold chain preservation throughout the entire process, frozen food has the characteristics of long shelf life, non-perishable, and convenient consumption, but it also poses greater challenges and higher requirements for packaging materials.
Common frozen food packaging materials
At present, the common frozen food packaging bags on the market mostly use the following material structures:
1. PET/PE
This structure is relatively common in quick-frozen food packaging. It has good moisture-proof, cold-resistant, low-temperature heat sealing properties and relatively low cost.
2. BOPP/PE, BOPP/CPP
This type of structure is moisture-proof, cold-resistant, has high tensile strength in low-temperature heat sealing, and is relatively economical in cost. Among them, the appearance and feel of packaging bags with BOPP/PE structure are better than those with PET/PE structure, which can improve product quality.
3. PET/VMPET/CPE, BOPP/VMPET/CPE
Due to the existence of the aluminum plating layer, this type of structure has beautiful surface printing, but its low-temperature heat sealing performance is slightly poorer and the cost is higher, so its utilization rate is relatively low.
4. NY/PE, PET/NY/LLDPE, PET/NY/AL/PE, NY/PE
Packaging with this type of structure is resistant to freezing and impact. Due to the presence of the NY layer, its puncture resistance is very good, but the cost is relatively high. It is generally used for packaging angular or heavier products.
In addition, there is also a simple PE bag, which is generally used as an outer packaging bag for vegetables and simple frozen foods.
In addition to packaging bags, some frozen foods require the use of blister trays. The most commonly used tray material is PP. Food-grade PP is more hygienic and can be used at low temperatures of -30°C. There are also PET and other materials. As a general transportation package, corrugated cartons are the first factors to be considered for frozen food transportation packaging due to their shock-proof, pressure-resistant properties and cost advantages.
Testing standards for frozen food packaging
Qualified goods must have qualified packaging. In addition to testing the product itself, product testing must also test the packaging. Only after passing the test can it enter the circulation field.
At present, there are no special national standards for the testing of frozen food packaging. Industry experts are working with frozen food manufacturers to actively promote the formulation of industry standards. Therefore, when purchasing packaging, frozen food manufacturers must meet the general national standards for relevant packaging materials.
For example:
GB 9685-2008 "Hygienic Standards for the Use of Additives for Food Containers and Packaging Materials" stipulates hygienic standards for additives used in food containers and packaging materials;
GB/T 10004-2008 "Plastic Composite Film for Packaging, Dry Lamination for Bags, and Extrusion Lamination" specifies composite films, bags, and plastic composite films made by dry lamination and co-extrusion lamination processes that do not contain paper base and aluminum foil. , the appearance and physical indicators of the bag, and stipulates the amount of residual solvent in the composite bag and film;
GB 9688-1988 "Hygienic Standard for Polypropylene Molded Products for Food Packaging" stipulates the physical and chemical indicators of PP molded packaging for food, which can be used as the basis for the formulation of standards for PP blister trays for designated frozen foods;
GB/T 4857.3-4 and GB/T 6545-1998 "Method for determination of bursting strength of corrugated cardboard" respectively provide the requirements for stacking strength and bursting strength of corrugated cardboard boxes.
In addition, in actual operations, frozen food manufacturers will also formulate some corporate standards that suit their own conditions based on actual needs, such as quantitative requirements for blister trays, foam buckets and other molded products.
Two major problems cannot be ignored
1. food dry consumption, "frozen burning" phenomenon
Frozen storage can greatly limit the growth and reproduction of microorganisms and reduce the rate of food spoilage. However, for some freezing process, the dry consumption and oxidation of food will become more serious with the extension of freezing time.
In the freezer, the distribution of temperature and water vapor partial pressure exists such: the food surface> surrounding air> cooler. On the one hand, this is due to the heat from the food surface is transferred to the surrounding air, and the temperature is further reduced; on the other hand, the partial pressure difference between the water vapor present in the food surface and the surrounding air causes water, ice crystal evaporation and sublimation into water vapor into the air.
So far, the air containing more water vapor decreases its density and moves over the freezer. At the low temperature of the cooler, the water vapor contacts the surface of the cooler and condenses into frost to attach it, and the air density increases, thus it sinks and makes contact with the food again. This process will be repeated, circulation, the water on the surface of the food is constantly lost, the weight is reduced, this phenomenon is "dry consumption". In the process of continuous dry consumption phenomenon, the surface of food will gradually become porous tissue, increasing the contact area with oxygen, accelerate the oxidation of food fat, pigment, surface browning, protein denaturation, this phenomenon is "freezing burning".
Due to the transfer of water vapor and the oxidation reaction of oxygen in the air are the fundamental causes of the above phenomenon, so as a barrier between frozen food and the outside world, the plastic packaging materials used in its internal packaging should have good water vapor and oxygen blocking performance.
2. The impact of frozen storage environment on the mechanical strength of packaging materials
As we all know, plastics will become brittle and prone to breakage when exposed to low temperature environments for a long time, and their physical properties will drop sharply, which reflects the weakness of plastic materials in terms of poor cold resistance. Usually, the cold resistance of plastics is expressed by the embrittlement temperature. As the temperature decreases, the plastic becomes brittle and easy to break due to the decrease in the mobility of the polymer molecular chain. Under the specified impact strength, 50% of the plastic will undergo brittle failure. The temperature at this time is the brittle temperature. That is, the lower limit of temperature for normal use of plastic materials. If the packaging materials used for frozen food have poor cold resistance, during the later transportation and loading and unloading processes, the sharp protrusions of the frozen food can easily puncture the packaging, causing leakage problems and accelerating food spoilage.
During storage and transportation, frozen food is packaged in corrugated boxes. The temperature of the cold storage is generally set at -24℃~-18℃. In cold storage, corrugated boxes will gradually absorb moisture from the environment, and usually reach moisture balance in 4 days. According to relevant literature, when a corrugated carton reaches a moisture balance, its moisture content will increase by 2% to 3% compared to a dry state. With the extension of refrigeration time, the edge pressure strength, compressive strength, and bonding strength of corrugated cartons will gradually decrease, and will decrease by 31%, 50%, and 21% respectively after 4 days. This means that after entering the cold storage, the mechanical strength of corrugated cartons will decrease. The strength is affected to a certain extent, which increases the potential risk of box collapse in the later stage.
Frozen food will undergo multiple loading and unloading operations during transportation from the cold storage to the sales location. The constant changes in temperature differences cause the water vapor in the air around the corrugated carton to condense on the surface of the carton, and the moisture content of the carton quickly rises to about 19%. , its edge pressure strength will drop by about 23% to 25%. At this time, the mechanical strength of the corrugated box will be further damaged, increasing the probability of box collapse. In addition, during the carton stacking process, the upper cartons exert continuous static pressure on the lower cartons. When the cartons absorb moisture and reduce their pressure resistance, the bottom cartons will be deformed and crushed first. According to statistics, the economic losses caused by the collapse of cartons due to moisture absorption and ultra-high stacking account for about 20% of the total losses in the circulation process.
Solutions
In order to minimize the frequency of the above two major problems and ensure the safety of frozen food, you can start from the following aspects.
1. Choose inner packaging materials with high barrier and high strength.
There are many types of packaging materials with different properties. Only by understanding the physical properties of various packaging materials can we choose reasonable materials according to the protection requirements of frozen food, so that they can not only maintain the flavor and quality of the food, but also reflect the value of the product.
At present, plastic flexible packaging used in the field of frozen food is mainly divided into three categories:
The first type is single-layer packaging bags, such as PE bags, which have relatively poor barrier effects and are commonly used for vegetable packaging;
The second category is composite soft plastic packaging bags, which use adhesive to bond two or more layers of plastic film materials together, such as OPP/LLDPE, NY/LLDPE, etc., which have relatively good moisture-proof, cold-resistant, and puncture-resistant properties;
The third category is multi-layer co-extruded flexible plastic packaging bags, in which raw materials with different functions such as PA, PE, PP, PET, EVOH, etc. are melted and extruded separately, merged at the main die, and then combined together after blow molding and cooling. , this type of material does not use adhesives and has the characteristics of no pollution, high barrier, high strength, high and low temperature resistance, etc.
Data shows that in developed countries and regions, the use of third-category packaging accounts for about 40% of the total frozen food packaging, while in my country it only accounts for about 6% and needs to be further promoted.
With the continuous advancement of science and technology, new materials are emerging one after another, and edible packaging film is one of the representatives. It uses biodegradable polysaccharides, proteins or lipids as the matrix, and forms a protective film on the surface of frozen foods using natural edible substances as raw materials and through intermolecular interactions through wrapping, dipping, coating or spraying. , to control moisture transfer and oxygen penetration. This kind of film has obvious water resistance and strong gas permeability resistance. The most important thing is that it can be eaten with frozen food without any pollution, and has broad application prospects.
2. Improve the cold resistance and mechanical strength of the inner packaging materials
Method one, choose a reasonable compound or co-extruded raw materials.
Nylon, LLDPE, EVA all have excellent low temperature resistance and tear resistance and impact resistance. The addition of such raw materials in the composite or co-extrusion process can effectively improve the waterproof and air resistance and mechanical strength of packaging materials.
Method two, appropriately increase the proportion of plasticizers. Plasticizer is mainly used to weaken the subvalent bond between polymer molecules, so as to increase the mobility of polymer molecular chain, reduce crystallization, manifested as the decrease of polymer hardness, modulus embrittlement temperature, as well as the improvement of elongation and flexibility.
3. improve the compressive strength of corrugated boxes
At present, the market basically uses the slotted corrugated carton to transport frozen food, this carton is surrounded by four corrugated board nails, up and down by four broken wing cross folding sealing synthetic type. Through literature analysis and test verification, it can be found that the carton collapse occurs in the four cardboard placed vertically in the box structure, so strengthening the compressive strength of this place can effectively improve the overall compressive strength of the carton. Specifically, first of all, in the carton wall around the addition of the ring sleeve, it is recommended to use A corrugated cardboard, its elasticity, shock absorption, can prevent frozen food sharp puncture damp cardboard. Secondly, the box type carton structure can be used, this box type is usually made of multiple pieces of corrugated board, the box body and the box cover are separated, through the cover for use. Test shows that under the same packaging conditions, the compressive strength of the closed structure carton is about 2 times that of the slotted structure carton.
4. Strengthen packaging testing
Packaging is of great significance to frozen food, so the state has formulated GB / T24617-2009 Frozen Food Logistics Packaging, Mark, Transportation and Storage, SN / T0715-1997 Export Frozen Food Commodity Transportation Packaging Inspection Regulations and other relevant standards and regulations, by setting the minimum requirements of packaging material performance, to ensure the quality of the whole process from the supply of packaging raw materials, packaging process and packaging effect. To this, the enterprise should establish perfect packaging quality control laboratory, equipped with three cavity integrated block structure of oxygen / water vapor transmittance tester, intelligent electronic tension test machine, carton compressor test machine, for frozen packaging material barrier performance, compression resistance, puncture resistance, tear resistance, impact resistance and a series of tests.
To sum up, the packaging materials of frozen food are faced with many new needs and new problems in the application process. Studying and solving these problems are of great benefit to improve the storage and transportation quality of frozen food. In addition, improving the packaging testing process, the establishment of various types of packaging materials testing data system, will also provide a research basis for the future material selection and quality control.
Post time: Dec-23-2023
