Food Packaging Technology 3(2+1)

Lesson- 4 Packaging systems

4.1 Aseptic packaging

Aseptic packaging is a method in which food is sterilized or commercially sterilized outside of the can, usually in a continuous process, and then aseptically placed in previously sterilized containers which are subsequently sealed in an aseptic environment. After cooling, the sterile food product is pumped to an aseptic packaging system where the food is filled and hermetically sealed into previously sterilized containers. Aseptically processed foods can be packaged in the same types of containers used for retorted foods. However, another advantage of aseptically processed foods is that they can be packaged in containers that do not have to survive the conditions of a retort. These include LDPE/Pb/LDPE/AL/LDPE laminate cartons and multilayer plastic flexible packaging that has cost and convenience advantages.

The disadvantage of these packages is that they are not as easily recycled as metal and glass containers. Aseptic filling systems have also been developed for HDPE and PET bottles. Aseptic filling of PET containers may have a cost advantage over hot filling of heat-set PET containers. Another advantage of aseptically processed foods is that they can be filled into drums, railroad tank cars, tank trucks and silos that have been previously sterilized with steam. The food can be later reprocessed and packaged to meet market demands. The sterilization agents available for aseptic packaging include heat, chemical treatment with hydrogen peroxide and high energy irradiation (UV light or ionizing (gamma) irradiation). A combination of hydrogen peroxide and mild heat is most commonly used with plastic and paperboard-based laminate packaging.

The most commercially successful form of aseptic packaging utilizes paper and plastic materials which are sterilizes, formed, filled and sealed in continuous operation. The package may be sterilized with heat or combination of heat and chemicals. In some cases, the disinfectant property of hydrogen peroxide (H₂O₂) is combined with heated air or ultra violet light to make lower temperatures effective in sterilizing these less heat resistant packaging materials.

Aseptic packaging is also used with the metal cans as well as large plastic and metal drums or large flexible pouches. Great quantities of food materials are used as intermediates in the production of further processed foods. This frequently requires packaging of such items as tomato paste or apricot puree in large containers. The food manufacturer then may use the tomato paste in the production of ketchup or the apricot puree in bakery products. If such large volumes were to be sterilized in drums, by the time the cold point reached sterilization temperature the product nearer the drum walls would be excessively burned. Such items can be quickly sterilized in efficient heat exchangers and aseptically packaged.

4.2 Modified Atmosphere Packaging

Modified atmosphere packaging (MAP) is a procedure which involves replacing air inside a package with a predetermined mixture of gases prior to sealing it. Once the package is sealed, no further control is exercised over the composition of the in-package atmosphere. However, this composition may change during storage as a result of respiration of the contents and/or solution of some of the gas in the product. Vacuum packaging is a procedure in which air is drawn out of the package prior to sealing but no other gases are introduced. This technique has been used for many years for products such as cured meats and cheese. It is not usually regarded as a form of MAP.

The gases involved in modified atmosphere packaging, as applied commercially are carbon dioxide, nitrogen and oxygen. Carbon dioxide reacts with water in the product to form carbonic acid which lowers the pH of the food. It also inhibits the growth of certain microorganisms, mainly moulds and some aerobic bacteria. Lactic acid bacteria are resistant to the gas and may replace aerobic spoilage bacteria in modified atmosphere packaged meat. Most yeasts are also resistant to carbon dioxide. Anaerobic bacteria, including food poisoning organisms, are little affected by carbon dioxide. Consequently, there is a potential health hazard in MAP products from these microorganisms. Moulds and some gram negative, aerobic bacteria, such as Pseudomonas spp, are inhibited by carbon dioxide concentrations in the range 5–50%. In general, the higher the concentration of the gas, the greater is its inhibitory power. The inhibition of bacteria by carbon dioxide increases as the temperature decreases.

Nitrogen has no direct effect on microorganisms or foods, other than to replace oxygen, which can inhibit the oxidation of fats. As its solubility in water is low, it is used as a bulking material to prevent the collapse of MAP packages when the carbon dioxide dissolves in the food. This is also useful in packages of sliced or ground food materials, such as cheese, which may consolidate under vacuum. Oxygen is included in MAP packages of red meat to maintain the red colour, which is due to the oxidation of the myoglobin pigments. It is also included in MAP packages of white fish, to reduce the risk of botulism. Other gases have antimicrobial effects. Carbon monoxide will inhibit the growth of many bacteria, yeasts and moulds, in concentrations as low as 1%.

However, due to its toxicity and explosive nature, it is not used commercially. Sulphur dioxide has been used to inhibit the growth of moulds and bacteria in some soft fruits and fruit juices.

Argon, helium, xenon and neon, have also been used in MAP of some foods. MAP packages are either thermoformed trays with heat-sealed lids or pouches. With the exception of packages for fresh produce, these trays and pouches need to be made of materials with low permeability to gases (CO₂, N₂, and O₂). Laminates are used, made of various combinations of polyester (PET), polyvinylidene chloride (PVdC), polyethylene (PE) and polyamide.

4.3 Active packaging

Active packaging refers to the incorporation of certain additives into packaging film or within packaging containers with the aim of maintaining and extending product shelf life. Packaging may be termed active when it performs some desired role in food preservation other than providing an inert barrier to external conditions. Active packaging includes additives or ‘freshness enhancers’ that are capable of scavenging oxygen, adsorbing carbon dioxide, moisture, ethylene and/or flavor/odor taints, releasing ethanol, sorbates, antioxidants and/or other preservatives and/or maintaining temperature control. Table 2.1 lists examples of active packaging systems, some of which may offer extended shelf life opportunities for new categories of food products.

 

 

 

Table 4.1 Selected active packaging systems

S.N.	Systems	Mechanisms	Food  application
1.	Oxygen scavengers	1. Iron-based 2. Metal/acid 3. Metal (e.g. platinum) catalyst 4. Ascorbate/metallic salts 5. Enzyme-based	Bread, cakes, cooked rice, biscuits, pizza, pasta, cheese, cured meats, cured fish, coffee, snack foods, dried foods and beverages
2.	Carbon dioxide scavengers/ emitters	1. Iron oxide/calcium hydroxide 2. Ferrous carbonate/metal halide 3. Calcium oxide/activated charcoal 4. Ascorbate/sodium bicarbonate	Coffee, fresh meats, fresh fish, nuts, other snack food products and sponge cakes
3.	Ethylene scavengers	1. Potassium permanganate 2. Activated carbon 3. Activated clays/zeolites	Fruit, vegetables and other horticultural products
4.	Preservative releasers	1. Organic acids 2. Silver zeolite 3. Spice and herb extracts 4. BHA/BHT antioxidants 5. Vitamin E antioxidant 6. Volatile chlorine dioxide/ sulphur dioxide	Cereals, meats, fish, bread, cheese, snack foods, fruit and vegetables
5.	Ethanol emitters	1. Alcohol spray 2. Encapsulated ethanol	Pizza crusts, cakes, bread, biscuits, fish and bakery products
6.	Moisture absorbers	1. PVA blanket 2. Activated clays and minerals 3. Silica gel	Fish, meats, poultry, snack foods, cereals, dried foods, sandwiches, fruit and vegetables
7.	Flavour/odour adsorbers	1. Cellulose triacetate 2. Acetylated paper 3. Citric acid 4. Ferrous salt/ascorbate 5. Activated carbon/clays/ zeolites	Fruit juices, fried snack foods, fish, cereals, poultry, dairy products and fruit
8.	Temperature control packaging	1. Non-woven plastics 2. Double-walled containers 3. Hydro fluorocarbon gas 4. Lime/water 5. Ammonium nitrate/water	Ready meals, meats, fish, poultry and beverages

The shelf life of packaged food is dependent on numerous factors, such as the intrinsic nature of the food (e.g. pH, water activity, nutrient content, occurrence of antimicrobial compounds, redox potential, respiration rate, biological structure) and extrinsic factors (e.g. storage temperature, relative humidity, surrounding gaseous composition). These factors directly influence the chemical, biochemical, physical and microbiological spoilage mechanisms of individual food products and their achievable shelf life. By carefully considering all of these factors, it is possible to evaluate existing and developing active packaging technologies and apply them for maintaining the quality and extending the shelf life of different food products.