METHODS OF PACKING PRODUCTS THAT MUST BE STORED AT LOW TEMPERATURES
Progress in the field of packaging technology as well as the increase in consumer demands pose a challenge to develop new packaging and modify traditional food packaging systems.
Innovations play a special role in improving the functionality of packaging, but also in improving their barrier, strength and aging resistance properties, while simultaneously searching for new materials that would solve ecological problems.
1. VACUUM PACKING
2. ACTIVE AND INTELLIGENT PACKAGING
3. CONVENIENT FOOD PACKAGING
Authors:
Prof. Ph.D. JACEK KONDRATOWICZ
MSc. EWA Kościelak
Department of Commodity Science of Animal Raw Materials
University of Warmia and Mazury in Olsztyn
The article comes from the publication: "Refrigeration", volume XL 2005, no. 8
1. VACUUM PACKING
Regardless of the classic methods of packaging food stored at low temperatures, special packaging techniques using a vacuum inside the package are increasingly used [Postolski 1998].
Vacuum packaging involves evacuating air from the package, which is then tightly closed, usually by heat sealing. Of course, an indispensable condition is the use of packaging material with a sufficiently high barrier to gases, enabling the vacuum to be maintained for as long as possible during long-term refrigerated storage of food.
Removing a significant amount of air from packaging can be considered as modifying the atmosphere around the packaged product.
According to Czerniawski and other authors [1998], vacuum packaging enables maintaining a higher level of quality of a food product during its natural shelf life, rather than being a way to extend this period. This is due to the inability to completely remove oxygen from the packaging, even when using a deep vacuum, and the impact of other factors causing product spoilage, such as the development of anaerobic microorganisms.
Compared to traditional packaging, vacuum packaging significantly increases the durability of frozen products (e.g. frozen fatty fish, shrimps, vegetables, mushrooms, aromatic herbs). The disadvantage of vacuum packaging is their sensitivity to external pressure and their tendency to stick together. Hence, packaging filled with an inert protective gas is often preferred. This applies primarily to oxygen-sensitive products with a high fat content, brittle products susceptible to deformation under the influence of external pressure, and loose products with sharp edges, which are easily damaged in vacuum packaging due to tight adhesion. The latter include, among others: frozen meat semi-finished products [Postolski 1998].
The packaging materials used in the vacuum packaging system are primarily multi-layer plastics. a type of packaging with a multi-layer structure may prove to be an alternative to currently used packaging materials. The properties of a new laminate depend primarily on the properties of its component materials. This contributed to obtaining packaging with the most desirable features in refrigeration technology, namely:
• in the freezing process, it provides little insulation in heat exchange thanks to the high thermal conductivity coefficient,
• during storage and in trade, it creates the greatest possible limitation of heat transfer to the product from the environment,
• has low permeability to gases and water vapor and protects the packaged goods against drying out and losing weight,
• has low oxygen permeability and protects the product against oxidation processes of fats and vitamins,
• provides good protection against loss of odors,
• comprehensively protects the product against harmful environmental influences (also resistant to low and high temperatures) [Królicki 2003].
Laminates produced using the co-extrusion technique are used to produce trays and bags that perfectly meet the requirements of frozen and chilled food.
Paper-plastic laminates have similar properties and the same applications. Multi-layer co-extruded barrier films are used for vacuum packaging of food products that are thermally preserved after packaging [Czerniawski et al.]
Materials refined with aluminum are used in vacuum packaging. They include a wide group of products containing Al foil combined with plastic and paper foils, as well as metalized foil and papers.
The main goals of refining packaging materials include:
• better protection of packaged products,
• adapting packaging materials to new, more favorable packaging systems and food preservation methods,
• providing packaged products with such presentation values that would enable them not only to survive on an increasingly competitive market, but also to increase their sales [Czerniawski et al. 1998].
The disadvantage of refined materials is problems with their disposal. Despite this, they belong to the group of valuable materials due to their barrier properties - an important property of multi-layer materials, which is determined by the layer with the lowest permeability. In relation to the combinations containing Al foil, it is the layer with the lowest permeability [Jakowski 2003].
Vacuum packaging also uses trays made of PE or PP aluminum foil, i.e. with a heat-sealable layer that allows the package to be hermetically closed. They are used primarily for packaging deep-frozen food in the form of meat products, delicatessen products intended for baking, ready-made dinner dishes, as well as cakes and desserts [Czerniawski et al. 1998].
American scientists conducted an experiment on raw turkey breast, which was vacuum packed in nylon/polyethylene laminate bags. The meat packed in this way was then irradiated with ionizing radiation and frozen. It turned out that meat preserved using the presented technique was of better quality, fat hydrolysis occurred to a lesser extent during storage, nutrient losses were reduced, and the color and smell did not deteriorate. During culinary processes, this meat showed less juice leakage and was characterized by a more intense taste and smell.
Vacuum-packed, previously irradiated frozen foods had better quality and shelf life [Nam 2001].
Despite many new solutions, classic packaging in the form of vacuum packaging bags is still used in the industry:
a) laminate of cellophane and polyethylene,
b) PET/PE laminate,
c) foils made of VDC copolymers,
d) PET and PA films in the form of sleeves in which air can be evacuated by thermal shrinking on the packaged product,
e) PA/PE laminates [Czerniawski et al. 1998].
2. ACTIVE AND INTELLIGENT PACKAGING
The packaging industry has been developing very intensively in recent years, mainly due to advanced technology. As a result, new generations of packaging are created that help maintain or even improve the quality of the packaged product, which is an essential advantage, especially in the food industry. Active and intelligent packaging is a perfect example here:
Active packaging, also called interactive, is packaging in which the product, packaging and surroundings interact with each other. Their task is to influence the product in a targeted manner to ensure its higher quality and to extend its shelf life and shelf life. These packages can control and respond to changes occurring inside. Unlike traditional ones, active packaging materials react with the internal atmosphere and the product, extending its durability [Zmarlicki 2000].
Packaging technologies using active materials may include:
• inclusion in the packaging or packaging material of chemical or enzymatic substances that adsorb and remove oxygen from the atmosphere inside the packaging,
• including substances that produce or adsorb carbon dioxide in the packaging,
• controlling the ethylene content in the packaging by adsorption on an oxidizing agent or an organometallic compound,
• release of ethanol in the form of vapor into the packaging as a factor inhibiting the development of microflora,
• the use of preservatives, bactericidal substances and antioxidants released from the packaging material,
• use of humidity regulators,
• use of technology enabling odor and taste control,
• use of light absorbers,
• use of foils that release a mineral substance that protects the color of the product,
• refining the foil surface to change its permeability, using susceptors, i.e. foils controlling the heating of the product in a microwave oven [Korzeniowski 2003].
Complete removal of oxygen, in the case of vacuum packaging and surrounding with inert gas, is practically impossible. In many cases, leaving even a small amount of oxygen in the packaging has a detrimental effect on the quality of the product.
Removing this residue may have a beneficial effect on protection against:
• growth of microorganisms,
• deterioration of nutritional properties,
• fat oxidation,
• colors,
• change in smell and taste,
• the impact of pests.
By introducing a chemical that reacts with oxygen into the packaging, the level of its content can be reduced to a minimum. For this purpose, ferrous compounds are used, among others, such as ferrous oxide and ferrous carbonate, combined with appropriate catalytic systems to initiate the reaction. Non-metallic and organometallic agents are also used. Depending on the type of substance and the way it is introduced into the packaging, the oxygen residue in the packaging is reduced in order to change its permeability.
In addition to "smart" foils, there are so-called "forgiving" foils - resistant to a wide range of temperatures, both in heating tunnels and freezers. Foils of this type change gas permeability with temperature changes, even to a small extent, and this is related to the reversible change of the crystalline structure at a lower temperature to an amorphous one at a higher temperature [Ucherek 2002]. In order to inhibit the development of undesirable microorganisms in food, substances such as lysozyme, heavy metal ions and fungicides can be incorporated into packaging materials or applied to their surface. Attempts are also made to use radioactive elements as antibacterial agents in the production of packaging films. In Japan, the most commonly used compound of this type incorporated into packaging films is silver zeolite, which is characterized by a wide range of antibacterial properties. An equally well-known compound with a similar effect is ethanol, which can be placed in packaging in the form of sachets emitting ethanol vapors. Antibacterial films can potentially be used for packaging food stored at low temperatures. The packaging should use foils with a high barrier to water vapor or active packaging that regulates the water content in the atmosphere surrounding the product.
Desiccators prevent the accumulation of water generated during defrosting, which helps maintain the attractive appearance of the product in the packaging. Desiccators can be in the form of bags with moisture absorbers (polyacrylic salts and starch copolymers) or can be placed between two layers of packaging foil [Panfil-Kuncewicz 2001].
Antioxidants are widely used food additives that increase the oxidative stability of fats and extend the shelf life. Antioxidants are incorporated into plastic films during their production to prevent polymer oxidation. The anti-oxidant properties of the foil result from the ability of antioxidants to migrate to the surface of the packaging material and then to the surface layers of the product [Zmarlicki 2000].
The absorption of food odors by polymer packaging may cause changes in the organoleptic properties of many products. This phenomenon can also be used as a way to selectively remove unwanted odors. Compounds are incorporated into the films used in packaging frozen or chilled meat and fish, e.g. binding amines and aldehydes resulting from the degradation of muscle proteins. This type of Japanese absorbers contain iron salts and lemon or ascorbic acid [Panfil-Kuncewicz 2001].
A special group among active packaging is intelligent packaging, which owes its name to its function of measuring a specific factor and signaling the result. The operation of these packagings is related to the use of interactive indicators, most often colored, enabling the assessment of product quality.
There are two types of intelligent packaging, namely:
A. time and temperature integrators (TTI)
B. freshness indicators.
The principle of operation of TTI is to irreversibly change its properties under the influence of a temperature higher than the set value or as a result of the thermal effect accumulated during storage and transport. The consequence of this change is a visual effect proportional to its intensity - most often expressed by discoloration of the marked field of the label. The mentioned integrators are mainly used in the packaging of frozen and refrigerated food. They allow, among others: to register the fact of temporary defrosting of the product. TTI allows you to monitor any deviations from the optimal temperature throughout the entire distribution cycle, integrating their intensity and time of occurrence. The integrator's signal indirectly informs about the shortening of the product's quality-safe storage period. The operation of freshness indicators is usually based on detecting the presence of microbial metabolites, i.e. carbon and sulfur dioxide, ammonia, amines, hydrogen sulphide, organic acids, ethanol, toxins and enzymes. The indicator's indicator system may use electronic and optical detectors, as well as colored compounds that are formed in reaction with the substance absorbed from the inside of the packaging [Ucherek 2002].
Smart packaging also makes it possible to detect packaging leaks. The most popular are oxygen indicators, e.g. Ageless Eye - a "non-aging eye" that changes color from pink to blue when oxygen enters the packaging [Cichoń 2000].
Representatives of logistics networks are increasingly interested in this type of packaging, where the product is monitored 24 hours a day using an electronic chip.
The materials needed for the production of active packaging do not have to meet too high requirements. Most often, these are traditionally used foils. Materials with good gas barrier properties are most suitable. The selection of the appropriate material largely depends on the type of product being packaged. Numerous studies are underway to find an appropriate technological base for active polymer films.
Such foils should have:
• appropriate strength,
• the best impermeability,
• appropriate amount of active ingredients with high diffusion mobility and the ability to be released from the foil [Korzeniowski 2003].
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