B.P.F.Day, Campden and Chorleywood Food Research Association
In recent years, consumer demand for perishable chilled foods, which are considered fresh, healthy and comfortable, has greatly increased. Large suppliers meet this consumer demand by supplying an increasingly wide range of chilled processed foods to retail. A large variety of chilled products is accompanied by a wide variety of packaging materials and forms used to increase the attractiveness of packaged products in refrigerated display cases. This chapter provides an overview of the requirements and types of packaging materials and forms used in the production of refrigerated food. In addition, the chapter describes both well-known and new packaging technologies for extending the shelf life of chilled products, such as packaging in a controlled gaseous environment (CGR), in vacuum, into a vacuum-formed film on a substrate and active packaging, with new developments marked especially. Processing and packaging methods based on heat treatment to increase the shelf life of chilled food products (hot filling, pasteurization under vacuum and in packaging) are beyond the scope of this chapter and are described in the chapter “Microbiological risks and design of safe technological processes.”
to packaging materials requirements for chilled products
Table. 6.1 are the basic requirements for packaging chilled products . Depending on the packaged product, not all these requirements must be met.
|♦ contain product||♦ integrity integrity|
|♦ Be compatible with the product||♦ Prevent microbiological contamination|
|♦ Be non-toxic||♦ Protect from odors and tastes|
|♦ Move without interference along the packaging lines||♦ Prevent dirt from entering|
|♦ withstand packaging processes||♦ Prevent insect and rodent contamination|
|♦ To withstand the load during distribution||♦ Be cost effective|
|♦ Prevent mechanical damage||♦ To be attractive to buyers|
|♦ Have proper gas permeability||♦ Carry product information|
|♦ Prevent loss or collection of moisture||♦ Make a fake noticeable|
|♦ Protect from light||♦ Easy to open|
|♦ Prevent fogging||♦ Withstand operating temperatures|
The material must keep the product free of leaks, be non-toxic and have sufficient mechanical strength to protect the product and to withstand the stresses of production, storage, transportation and display.
Since some packages require a certain degree of porosity in order for moisture exchange or gas exchange to occur, the packaging materials used in these situations must have appropriate permeability properties. Most CGS packages require that moisture or gases are retained in the package, and therefore the packaging materials used must have appropriate barrier properties (moisture or gas impermeability). Special requirements for packaging with CSGs are described below. Depending on the type of cooled product, it may be that the packaging material must withstand the high temperatures that it undergoes when hot-filled, pasteurized in a package or re-heated before use. It may be necessary for the packaging material (especially for high-speed continuous operations) to be compatible with form-filling and sealing machines. Packing must be sealed, but at the same time it should be easy to open. It may be necessary to re-seal the pack when it is stored at home after opening. In addition, due to an increase in the number of cases of deliberate contamination, packaging is desirable to protect against intentional opening or to make it noticeable. Packaging is the main means of demonstrating the cooled product contained in it, a source of product information and advertising at points of sale. Therefore, when choosing a material, its transparency and suitability for printing should be taken into account. Finally, the packaging material must be cost effective relative to the corresponding product inside it. For example, a ready-to-eat product sold at a high price may justify a significantly higher cost of packaging than a yoghurt dessert sold much cheaper.
Packaging materials for refrigerated products
After determining the requirements for the packaging of the cooled product, the next step is to find the type of packaging material that provides the necessary characteristics. Almost always possible to use several types of materials. Packaging materials made from paper, glass, metal or plastic have their own individual advantages, which should be considered when choosing a material.
The main technical characteristics of modern packaging materials for chilled food products are given in Table. 6.2, and the main types of materials (and their reductions) are given in Table. 6.3 . For any particular product, usually several materials can be used individually or in the form of a composite.
6.2 Table. Comparison of packaging materials for refrigerated products
|Material||The main technical advantages|
|Aluminum||Tightness, light weight, the axial strength of the container can withstand internal pressure|
|Paper||A wide variety of paper grades, simple decoration, the addition to all other packaging materials, light weight|
|Semi-rigid plastics||The properties depend on the type of plastic, the choice of the form of packaging, manufacturing directly to the food industry, light weight|
|Flexible plastic||Properties vary due to a combination of very easy packing, individual size|
|Glass||Chemical inertness, impermeability, content visibility, the axial strength of the container can withstand an internal vacuum, reusability|
6.3 Table. Packaging materials for refrigerated products
|Aluminium Foil||HDPE (high density polyethylene, HDPE)|
|cardboard||HIPS (polystyrene udaroprochnыy UpPS)|
|Cellulose||LDPE (low density polyethylene, LDPE)|
|cellulose fiber||LLDPE (linear low density polyethylene,|
|Natural materials||MXDE (modified nylon, MN)|
|Paper||OPP (oriented polypropylene, EPP)|
|metallised cardboard||OPS (oriented polystyrene, OPS)|
|Metallized film||RA (poliamidnejlon, PA)|
|Steel||PC (polycarbonate, PC)|
|ABS (acrylonitrile-butadiene-styrene, ABS)||CE (polyethylene, PE)|
|Aretha (amorphous polyethylene terephthalate||PET (polyethylene terephthalate, PET)|
|(Apet))||PETG (modified times, MPÉT)|
|SA (acetilcellûloza, AC)||PP (polypropylene, PP)|
|Shit (crystallized PET)||PS (polystyrene, PS)|
|CPP (cast polypropylene, LPP)||PVC (polyvinyl chloride, PVC)|
|EPS (penopolistirol, PPS)||PVDC (polyvinylidene chloride, PVDC)|
|EVA (ethylene vinyl acetate, EVA)||UPVC (neplastifitsirovannыy PVC|
|EVOH (ethylene vinyl alcohol, EVOH)||NpPVH)|
In the packaging of chilled food products are widely used paper and cardboard. They are easy to decorate and, in addition, they can serve as a supplement to all other packaging materials in the form of labels, cardboard boxes, trays or outer packaging. They can be supplied with coatings (such as wax, silicone and PVDC) or as laminates with aluminum foil or flexible plastics. Such a coating or lamination allows thermo-bonding and improves oxygen, moisture or grease resistance. For example, butter is traditionally packaged in wax paper or multi-layer aluminized paper.
Double trays of heat-resistant cardboard can be made of cardboard coated with polyethylene terephthalate (PET) by extrusion. They can withstand temperatures up to 220 ° C and are therefore suitable for heating ready-to-eat chilled foods in a microwave and conventional oven.
Another application of cardboard in the packaging of chilled products is susceptor trays, which allow you to fry and make crispy meat or dough products in a microwave oven - for example, pizza and pies. A typical microwave tray susceptor is made of cardboard covered with metallized film.
Glass cans and bottles are the oldest form of packaging with extremely low permeability. Their advantages include good axial strength, the ability to see the product, the ability to reuse and chemical inertness. Refillable glass bottles for pasteurized milk are still widely used in the UK. Aluminum lids and plugs make opening easy, and tools that make opening attempts explicit (for example, flip-open lids) ensure consumer safety. The main disadvantage of glass packaging is its destruction upon impact, but new glass technologies and plastic sheaths (stockings) made of PVC or PPP helped reduce the glass breakage.
Materials based on a metal
Pressed trays of aluminum foil have long been used for packaging ready-made frozen foods and hot takeaway food, as well as for many chilled ready-made foods. Their temperature stability makes them ideal for heating in a conventional oven, but when used in microwave ovens, precautions should be taken to avoid arcing. Developed guidelines for using foil containers in microwave ovens . In some circumstances, aluminum foil makes it possible to more uniformly heat than microwave-transparent trays . For many dairy products, such as butter, margarine and cheese, aluminum foil or paper laminated with aluminum is used. Aluminum foil is also used in carton composite containers for chilled fruit juices and dairy drinks. In addition, aluminum or steel aerosol cans are used for chilled creams (cream) and processed cheese.
For the packaging of most refrigerated products, the most preferred material is plastic. Chilled desserts, ready meals, dairy products, meats, seafood, pasta dishes, poultry, fruits and vegetables are often packaged in plastic or materials based on it. For the manufacture of semi-rigid plastic containers for refrigerated products, mainly polyethylene (PE), polypropylene (PP), polystyrene (PS), PVC, PET and a copolymer of acrylonitrile, butadiene and styrene (ABS) are used. Other plastics, such as polycarbonate (PC), are used in small quantities.
The container is issued in the form of the most various bottles, cans, trays and other forms. Thermoforming, injection molding and molding on a sandblasting machine enables food manufacturers to make packaging in their production. Flexible plastics are the cheapest protective material, and they can be used for packaging perishable chilled products in a vacuum or in a CSG. Multilayer materials are usually obtained by coextrusion or by coating, using PVDC or EVE layers to ensure oxygen-tightness. Plastics such as PE or PP can be metallized or laminated with foil to produce protective materials with high barrier properties (impermeability). The required specifications, size and shape of the package can be obtained in accordance with the specified requirements, which ensures cost effectiveness. Oxygen and vapor permeability of aluminum foil and some single-layer plastic films are given in Table. 6.4.
6.4 Table. Oxygen- and water vapor transmission rate of some packaging materials
|Packaging film (25 microns)||
Oxygen gas permeability l / (m2 • day • Pa) or cm3/ (M-2 • day-1 • ATM-1)
23 ° C: relative humidity 0%
Water vapor permeability
(G / m2* day-1)
38 ° C: relative humidity 90%
|Aluminium Foil||None. *||None. *|
|Aws||0,2 - 1,6 **||24 - 120|
|PVDC MM||0,8 - 9,2||0,3 - 3,2|
|PET PA6||50 - 100||20 30|
|MOTAPM||100 - 200||1,5 3,0|
|NpPVH RAS||120 - 160||22 35|
|PVC||2000 - 10 000 ***||200|
|Opp||2000 - 2500||7|
|PS||2500 - 5000||110 160|
|ops||2500 - 5000||170|
|PP||3000 - 3700||10 - 12|
|EMU with||12 000||110 160|
|Microperforated||20000 - 2000 000 ****||—|
* Depends on the porosity.
** Depending on the humidity.
*** Depending on the humidity and the level of plasticizer.
**** Depending on the degree of micro perforation.
The polymers used for packaging chilled foods are mainly thermoplastics, that is, they soften reversibly when heated, if there is no chemical destruction. PE is produced by polymerization of ethylene, and other thermoplastics, such as PP, PVDC, PS, PVC, EVA and ABS, are likewise polymerised from ethylene monomers. Plastics such as polyamide (PA), PC and PET, are obtained by a condensation reaction. For example, a PET film is made from PET resin, a product of the polycondensation of ethylene glycol and terephthalic acid, using a drawing process known as biaxial orientation.
Packing Methods for chilled foods
Packing in controlled atmosphere (CSG)
The method of packaging in a modified atmosphere is being used more and more. This method of food preservation is based on replacing air with another gaseous medium . Consumer demand for fresh, unaddressed products has led to the development of the CSG method to improve the appearance of food, reduce waste and increase shelf life .
Common refrigerated products currently available in the CGS package include beef, fish, seafood, poultry, crustaceans, offal, boiled and dried meat and fish, pasta dishes, pizza, kebabs, cheese, boiled and sliced vegetables products, dairy and bakery products, ready meals, whole and cooked fresh fruits and vegetables [1,11].
Gaseous media used in packaging according to the CSG method (Table 6.5) should be chosen to fit the specific food product, but for almost all
6.5 Table. Mixtures of gases for CSG chilled foods for Retail
|Meat (black / beef)||15 20||60 85||0 10|
|The meat (jerky)||20 35||—||65 80|
|The meat (cooked)||25 30||—||70 75|
|Gradually (sыrыe)||15 25||75 85||—|
|Poultry (white meat)||20 50||—||50 80|
|Poultry (dark, reddish)||25 35||65 75||—|
|Fish (white)||35 45||25 35||25 35|
|Fish (fatty)||35 45||—||55 65|
|Crustaceans and molluscs||35 45||25 35||25 35|
|Fish (steamed)||25 35||—||65 75|
|The pasta dishes (fresh)||25 35||—||65 75|
|Ready meals||25 35||65 75|
|Pizza||25 35||—||65 75|
|Quiche (pie with unsweetened custard and various fillings - vegetables, seafood, etc.)||25 35||65 75|
|Meat pies / cakes||25 35||—||65 75|
|Hard cheese)||25 35||—||65 75|
|Cream / cream||—||—||100|
|Fresh fruit / vegetables||3 10||210||80 95|
|Vegetables (cooked)||25 35||—||65 75|
products it some combination of carbon dioxide (CO2), Oxygen (O2) and nitrogen (N2) . Carbon dioxide has bacteriostatic and fungistatic properties and slows the growth of mold and aerobic bacteria. The combination of negative effects on various enzymatic and biochemical pathways leads to an increase in the lag-phase (the period of delay in reproduction of microorganisms) and the lifespan of one generation of susceptible microorganisms that cause spoilage of products. However, JI2 It does not slow down the growth of all kinds of microorganisms.
For example, the growth of lactic acid bacteria in the presence of improved S02 and low content of 02. Carbon dioxide has little effect on the growth of yeast cells. The inhibitory (inhibitory) effect of С02 is increased at low temperatures due to increasing its solubility in water and the formation of weak carbonic acid. The practical significance of this is that the CSG is not preclude the need for cooling. absorption S02 strongly depends on the water content of the product, and fat. Absorption of excess S02 can reduce the water-holding capacity of meat, which leads to unpleasant-looking drips. In addition, some dairy products may have a taste, and fruits and vegetables may suffer physiological damage due to high levels of С02. If products absorb excess CO2, the total volume inside the package is reduced, and the sealed package becomes oblate. In the CWG to suppress the growth of aerobic microorganisms that cause damage to the product, and reduce the rate of oxidative damage to the products, 0 levels2 usually set as low as possible. Nevertheless, there are exceptions: for example, oxygen is necessary for the respiration of fruits and vegetables, the preservation of color in red meat (for example, in beef) or to eliminate anaerobic conditions in packages of white fish obtained by the CGS method.
Nitrogen is an inert gas and in fact has a low solubility in water and in oil. In N2 CSG is mainly used to displace 02 to slow down aerobic and oxidative deterioration. Nitrogen also serves as a filler to prevent bundles from crushing. Other gases (carbon monoxide, ozone, ethylene oxide, nitrous oxide, helium, neon, argon, propylene oxide, ethanol vapor, hydrogen, sulfur dioxide and chlorine) have been used in experiments or on a limited scale commercially to increase the shelf life of a number of foods. For example, it was shown that carbon monoxide is very effective in preserving the color of red meat, preserving red strips of salmon and inhibiting the deterioration of plant tissue. However, the commercial use of most of these gases is significantly limited due to safety considerations, legal restrictions, adverse effects on organoleptic properties, or economic factors .
Argon (Ar) and zakisy nitrogen (N20) are defined as other additives and are in the EU permitted gases for use in the food industry. Air Liquide SA (Paris) has stimulated commercial interest in potential applications of the CSG method using argon and (to a lesser extent) N20. A large number of Air Liquide patents state that, compared with molecular nitrogen, argon can more effectively suppress enzymatic activity, microbial growth and destructive chemical reactions in some perishable foods. Although Ag is chemically inert, the Air Liquide study has shown that it does not have a biochemical effect (probably due to its similarity in atomic size to molecular oxygen and its higher density and solubility in water compared to N2 and 02) . Therefore, Ag is probably more efficient in driving out 02 with its position in the cells and enzyme receptors 02. As a consequence, it is likely suppressing oxidative deterioration reactions. In addition, it is believed that the Ar and N20 makes microorganisms more susceptible to antimicrobial agents. This possible sensitization is not yet fully understood, but may be associated with a change in the mobility of cell membranes of microorganisms, which affects the function and characteristics of the cell . Obviously, to better understand the potential positive effects of Ar and N20 needs an independent study.
The main characteristics that must be considered when choosing packaging materials for the CSG are listed below.
Gas permeability In most CSG applications, with the exception of fresh fruits and vegetables, it is desirable to maintain the medium originally created in the package for as long as possible. The correct composition of this medium will not last long if the packaging material allows it to change too quickly, and therefore the packaging material used with all types of products packaged according to the CSG method (except for fresh fruits and vegetables) must have barrier properties. Typically, the wrapping film consists of 15 / 2 PVDC coated with PET / 60 / w PE and the tray is made of 350 / x PVC / PE (fig. 6.1). PA / PVDH / LDPE, PA / PVDH / PEVP / EVS, OPP / PVDH / LDPE or PC / EVA / EVS, and VOPE, PET / EVA / LDPE, PVC / EVA / LDPE or PS / EVA / LDPE are used for trays .
The permeability of a particular packaging material depends on several factors — the nature of the gas, the structure and thickness of the material, temperature and relative humidity. Although С02,02 and N2 penetrate through the material with a completely different speed, order S02 > 02 >> N2 always saved, and the ratio of the permeability coefficients S02/02 and 02/N2 typically in the range of up to 3 5. Therefore, the material permeability S02 or> N2 can be estimated when only 0 permeability is known2. As a rule, the CSG method uses packaging materials with permeability for 02 less than 100 cm3 • m ~ 2 • day-1 • atm-1.
Packaging materials to achieve the desired barrier properties are usually laminated or coextruded get .
Unlike other perishable foods that are packaged in a controlled atmosphere, fresh fruit and vegetables continue to breathe after harvest, and any packaging it should be taken into account. Reduction of 02 and accumulation S02 - These are the natural consequences of continuing to breathe when storing fresh fruits or vegetables in hermetically sealed packaging. Such a change in the composition of the gaseous medium leads to a decrease in the rate of respiration and, consequently, to an increase in the shelf life of the fresh product. However, for the full realization of the CGS advantages for fresh products, a packaging film with appropriate permeability  should be chosen. Usually the key to successful packaging of fresh produce using the CSG method is maintaining an equilibrium environment with 2-10% 02/ С02 packaged. For products with a strong breath (eg, mushrooms, bean sprouts (mung especially), leeks, peas and broccoli), traditional film (LDPE, PVC, EVOH, OPP and acetate) are permeable enough. For such products with a strong breath are best packaging film
Fig. 6.1. The construction of a typical pallet and the closure of the film for use in the CSG
micro-perforation and high permeability, however, they are relatively expensive, permit loss of moisture and odor; in addition, through them microorganisms can get into already sealed packages when they are in wet conditions . A very interesting development for the packaging of freshly prepared products is related to the use of high-02 content XG (70-100%), which, as was recently shown, can overcome many of the shortcomings of the existing air and low-02 packaging. It has been shown that CGS with a high content of 02 suppresses enzymatic discoloration, prevents anaerobic fermentation reactions and inhibits the growth of microorganisms, resulting in an increase in the shelf life of finished products [8,9].
Paropronitsaemosta. Vapor permeability (water vapor penetration rate) is measured in g / (m2 • day-1) at a given temperature and relative humidity (W,%). Similar to gas permeability in different packaging materials there is a large scatter of vapor permeability (see tab. 6.4), however, there is no correlation between gas permeability and water permeability. Another complication is that some materials (for example, nylon and EVA) are sensitive to moisture, and their gas permeability depends on relative humidity .
Mechanical properties. Packaging materials used for packing according to the CSG method must have sufficient strength to withstand punctures and withstand multiple bends and mechanical stresses arising during transportation and loading and unloading operations. In addition, if you intend to use thermoformed trays, the film should be stretched evenly and not become too thin at the corners. Insufficient strength can lead to packaging damage and loss .
Reliability seal. To preserve the desired gas environment when using the CSG method, it is important to form a sealed package, and therefore it is important to choose the appropriate heat sealable packaging materials, controlling the sealing process. For example, in high-speed forming-filling-closing operations, it is important to take into account adhesion of the material at high temperatures. In addition, there is often a requirement for easy peeling of the material on the seam, so that the consumer can easily access the content. It is important to determine the relationship between flaking and seam integrity .
Transparency. For most products packaged using the CSG, it is desirable that the packaging is transparent and the product is clearly visible to the consumer. However, products with a high content of moisture stored at low temperatures often form misting of the inner surface of the package, which makes it difficult to see the product. Therefore, many films for packaging in the CWG are processed or covered with something to combat fogging and improve visibility. This treatment affects the wettability of the film, but does not affect its permeability .
To eliminate unwanted oxidative reactions caused by exposure to light, it is desirable to exclude light from entering certain foods packaged in CSGs (for example, green pasta and dried meat). In such cases, you can use light-protective colored or metallized films. Another phenomenon that may be caused by light is the greenhouse effect, which causes a rise in temperature in packages with chilled products , but it was concluded in  that this effect does not play an important role in increasing the temperatures of products exposed to refrigerated display cases.
Packing. The type of packaging used depends on the intended use of the product: for retail or for the catering industry. The most common options include flexible cushion packs, a bag-shaped box with a liner, semi-rigid trays and a sealing film (see fig. 6.1).
Suitable for microwave. The ability of CSG materials to withstand microwave heating is particularly important in the case of ready-to-eat products. For example, the low softening temperature of PVC makes common thermoformed trays made of PVC / LDPE unsuitable for heating in a microwave oven. Therefore, for products packaged in a CGM and intended to be heated in a microwave oven, materials with higher heat resistance, such as CCP, CET, and high-temperature polystyrene (HTPS), are used.