Packaging considers a very important role in food preservation. It also prevents food from physical damage and carries marketing and legislative information about the product. The packaging materials used in the food sector could be primarily glass, metal, plastic, and paperboard. All the materials used for packaging compete directly with one another, with achievement based on functionality, cost, and brand value (Coles et al., 2003).
Food packaging should look attractive, hygienic; explain about the nutritional values and product information for customer convenience which helps the product to evaluate. Modified atmosphere packaging (MAP) is the elimination and replacement of the atmosphere nearby the product before sealing in vapour-barrier materials. This process is also known as vacuum packaging (VP) because air is removed by vacuum or flushing and altered with another gas mixture before packaging. Controlled atmosphere packaging (CAP) applies continuous monitoring and control of the environment to retain stable gas atmosphere and other conditions includes temperature and humidity within the package. CAP is widely used to manage ripening and spoilage of fruits and vegetables (Mcmillin, 2008).
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There are three major gases involved in the modified atmosphere packaging (Co2, O2, and N2). Many foods spoil rapidly in air due to moisture loss or uptake, reaction with oxygen and the growth of aerobic microorganisms, i.e. bacteria and moulds. Microbial growth spoils the food colour, flavour, texture and nutritional values. To increase the quality of food and to maintain the shelf-life by reducing chemical reactions it is a must to store foods in a modified gaseous atmosphere (Rodriguez and Oliveira, 2009).
1.1 Types of Containers Used in Food Packaging:
Food packaging can be divided into primary, secondary and tertiary container. Food that comes into contact with the container directly is a primary container, example, a can or jar. It is a must that the containers are nontoxic and compatible with the food and not altering the colour and flavour. The outer box, case or wrapper that holds cans and jars collectively but does not contact the food directly is a secondary container. It plays an important role in the food packaging, where it should protect the primary containers from damage during shipment and storage. A group of several secondary boxes together in a pallet loads or shipping units are tertiary containers. Usually, a truck or similar equipment is used to move the tertiary loads (Potter, 1998).
1.2 Packaging Resources:
Depending on the features required for the future use, almost all the packs for MAP products are made of one or four polymers include Polyvinylchloride (PVC), Polyethylene terephthalate (PET), Polyethylene (PE) and Polypropylene (PP). Polyethylene is normally one of the components since it gives tight sealing and also a medium of control for the quality such as anti-fogging ability, peel ability and the ability to seal through a degree of contamination. Films such as double foil laminate give a barrier to the movement of gases in either way which may lead to unwanted anaerobic conditions being achieved within the packaging and the use of such barrier films based on the product involved (Phillips, 1996).
1.3 The antimicrobial packaging system:
Package systems are described by foods packed in flexible packages, cups, and cartons. Microbial contamination changes the shelf-life of food and increases the risk of food borne illness. There are various methods like drying, refrigeration, irradiation and adding salts cannot be applied to some food products like fresh meats. The promising form of active food packaging in meat products is antimicrobial packaging. Due to post-processing handling, microbial contamination occurs primarily, efforts have been tried to improve the safety by use of antibacterial sprays. Antimicrobial substances included into packaging materials can control microbial contamination by decreasing the growth rate and maximum growth population and extending the lag-phase of the target microorganism or by inactivating microorganisms by contact.
According to Ham (2000), several factors must be taken into account in the design or modelling of the antimicrobial film or package:
Chemical nature of films/coatings, casting process conditions and residual antimicrobial activity.
Characteristics of antimicrobial substances and foods.
Mass transfer coefficients
Physical properties of packaging materials.
These factors will help increase the shelf-life of the food products and produce antimicrobial films.
2.0 Gases Involved in Modified Atmosphere Packaging:
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The three gases oxygen, nitrogen and carbon dioxide are used in various combination and ratios depending on the products and the requests of the manufacturer. Other gases like ethanol, carbon monoxide, and sulphur dioxide can be found, but still the use of these gases is limited.
Oxygen controls the growth of anaerobic microorganisms and at the same time it allows the growth of aerobic microbes. Moreover, oxygen is responsible for some unwanted reactions in foods which include rapid ripening, oxidation, decay of fats and oils, oldness of fruits and vegetables and colour changes. It is usually avoided in the modified atmosphere packaging because of its negative effects on food quality. But still it is useful in surface mould ripened cheese. Nitrogen is an inert and tasteless gas without any antimicrobial activity. Nitrogen is used to shift oxygen and prevent package collapse and it is not very soluble in water. Carbon dioxide is soluble in both water and lipids and it is responsible for bacteriostatic effect on micro-organisms in modified atmospheres. The above mentioned three gases are common and easily available, economic and safe to use (Hall, 1997).
2.1 Effects of MAP in Food Products:
To maintain the quality of food products during the storage is mostly due to the control of the spoilage microorganisms. Even then a HACCP evaluation must be used to measure the potential safety risks of using MAP techniques for the products.
2.2 Fish Products:
Spoilage of fish results in the production of low molecular weight volatile compounds. The major bacteria found in the treated fish are aerobes. MAP can be used to control the breakdown of tissue (autolysis) and oxidative reactions. There are numerous microorganisms that are of particular importance when dealing with MAP of fish products, including C. botulinum. The replacement of oxygen by either nitrogen or nitrogen/carbon dioxide ends in anaerobic conditions that are conductive to the growth of C. botulinum. This can be eliminated by storing the products at 30c or below. In some cases, oxygen is also used in their MAP to reduce the growth of clostridia. Gas mixtures of 30% oxygen, 30% nitrogen and 40% carbon dioxide are used for non-processed fish which helps some of the fish products to increase the shelf life.
2.3 Meat Products:
The major cause of discolouration in meat products is due to oxidation. During the storage of MAP and vacuum-packed turkey breast there is a connection between colour stability and low microbiological contamination, but only in the turkey breast meat stored with 100% carbon dioxide and oxygen. Lipid oxidation is increased in MAP pork chops considered with air-stored; this harmful effect is balanced by a vitamin E supplement. Vacuum packed, cured sliced ham stored at 30c is acceptable for two weeks before maximal microbial counts occurred. At temperatures (100c) carbon dioxide packaging had no effect on shelf-life.
2.4 Fruits and Vegetables:
After harvesting, fruits and vegetables are metabolically active for long period due to both endogenous activities includes respiration and other factors like physical injury, storage temperature and water loss. The main applications of MAP are horticultural products, so that many of its thoughts refer to the metabolism of fruits and vegetables (e.g. respiration rate, transpiration rate). Reduction in oxygen level and increased levels of carbon dioxide in the environment conserve product quality because they slow down respiration, softening rates and improve chlorophyll and other pigment retention. The increased levels of carbon dioxide will reduce the rate of microbial growth and spoilage. In red peppers, MAP has shown improvement in carotenoids retention to maintain colour and reduced browning. The suitability of fruits and vegetables to the buyer is related to the growth of an aerobic spoilage micro flora so that the inhibitory effect of rising carbon dioxide concentration increases the shelf-life of vegetables such as cauliflower, broccoli and asparagus nearly seven days. The combination of storage time and temperature has been shown to be mainly important in extending the shelf-life of fruits in conditions of texture, weight loss, pH and other nutritional changes. For example, ciku can be stored for 4 weeks at 100c and 3 weeks at 150c when packaged under MAP, while storage without MAP is 1 week shorter at each temperature.
2.5 Cheese Product:
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Modified atmosphere packaging of cheese has been resulting in opposing conclusions, due to the larger amount of types of cheeses. Smith and Scott found on MAP of cheese that there is no rise in the refrigerated shelf-life of cottage cheese packed under 100% nitrogen or 100% carbon dioxide during 10-12 days, however there is a change in cheese flavour under 100% carbon dioxide. Mannheim and Soffer agreed that 100% carbon dioxide extends the shelf-life of cottage cheese at 80c by 150% without changing its sensory properties. On mould ripened cheese only few references are found regarding the effect of modified atmosphere packaging.
2.6 Bakery Products:
The growth of mould is the main factor preventive the shelf-life of bakery product. To avoid the growth of moulds and extend the shelf-life, high levels of carbon dioxide are used. The high solubility of carbon dioxide leads to flavour changes and results in package collapse and can be easily overcome by the usage of nitrogen.
2.7 Controlled atmosphere storage on cherry tomatoes:
To create controlled atmosphere a carbon dioxide incubator was used in which, temperature of the environment and carbon dioxide concentration can be monitored. In the incubator, the inoculated cherry tomatoes are placed in polypropylene trays on the shelves. Nearly fifteen inoculated cherry tomatoes were placed. The tomatoes will be treated for 10 days respectively. Then tomatoes were stored in controlled atmosphere containing 5% of carbon dioxide and 10-150c is optimum conditions for the storage of tomatoes.
3.0 Improvements in Modified Atmosphere Packaging techniques:
"The most significant area of development in modified atmosphere packaging techniques is the introduction of 'smart' or 'intelligent' or 'active' packaging systems to improve food safety during packaging and storage" (Sneller, 1986; Labuza, 1989; Summers, 1992).
These methods have been sorted out by the characteristic of the food or packaging influenced as oxygen scavengers; aroma removal; off-flavour removal; ethylene removal; carbon dioxide formation; ethanol emitters; water removal and edible films. Chemicals are included into the packaging in most of the 'smart' packaging, but not in contact with the products. The most common example of a smart packaging is the use of oxygen scavengers together with oxygen indicators. Biodegradable or edible films are the majority and current growth in this area. Edible coatings used to the food have been considered to create a modified atmosphere surrounding the food and these may be filled with antimicrobials or anti-oxidants to enhance the shelf-life of the product. There is also the possible for the use of negative microorganisms like lactic acid bacteria and bacteriocins which are effective in controlling the growth of Listeria monocytogenes in the meat products such as sausages. Still, the exchanges between antimicrobial metabolites and the components of food are not fully figured out and much stays to be done before the use of bacteriocins becomes usually accepted (Schillinger et al, 1996).
Consumers continue to demand foods that are minimally processed and fresh like quality. Packaging plays an important role in the food industry and helps to maintain the products in a Safeway for consumers and manufactures. MAP and CA is the key for packaging because all the products have different features and adoption level. These two packaging have been used in almost all the food industries and still in use. The major part involved in MAP and CA is the gases which were discussed earlier. Numerous type of packaging can be used in order to extend the effectiveness of food and for marketing.