Pulsed light will not penetrate deeply into foods but has potential for the treatment of surfaces - on the product, on packaging and on surfaces used for food preparation.
The light in question is broad spectrum white light - which can include light from the ultraviolet and infrared regions
Pulsed light treatments have been reported to reduce spoilage of baked products by inactivation of moulds, Salmonella on egg shell and chicken surfaces, and Pseudomonas on cottage cheese.
High voltage arc discharge processing involves rapidly discharging voltages through an electrode gap immersed in aqueous suspensions
The discharge is believed to generate intense physical waves and chemical changes (through electrolytic effects) which can inactivate microorganisms and enzymes without any significant rise in temperature.
shock waves can cause disintegration of food particles
Oscillating magnetic fields
Suggestions regarding this process are that a single pulse of an oscillating magnetic field
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could bring about a reduction in the number of viable microbes in the food within the field - multiple pulses could result in a commercially sterile product.
Studies have not universally corroborated these findings, with some suggesting that oscillating magnetic fields do not affect the microbial population or that the treatment can even stimulate microbial growth.
Such variation may be due either to differences in the treatment intensity or means of delivery, to differences in the media/food in which the microbes are treated, or to the target microbes.
The use of cold gas phase plasmas has been proposed for the inactivation of microorganisms
Cold plasma irradiation could be used to inactivate microorganisms on the surface of a range of materials, including packaging and food surfaces such as fruit, vegetables and meat.
Cold plasma irradiation has the advantage that it can be readily switched on and off, making it much more controllable than something like irradiation using a radioactive source.
Pasteurisation using CO2
The juice is supplied from a raw juice tank and is mixed with CO2 under pressure. The conditions are maintained such that the CO2 maintains a liquid state and does not freeze the product.
Inactivation of E. coli O157.H7, S. muenchen, S. agona and L. monocytogenes has been demonstrated using this technique.
The process has been shown to be effective for processing orange juice concentrate and orange juice with and without pulp
Factors affecting the choice of packaging material
Fresh, processed and manufactured foods are susceptible to mechanical damage. The bruising of soft fruits, the breakup of heat processed vegetables and the cracking of biscuits are examples. Such damage may result from sudden impacts or shocks during handling and transport, vibration during transport by road, rail and air and compression loads imposed when packages are stacked in warehouses or large transport vehicles. Appropriate packaging can reduce the incidence and extent of such mechanical damage. Packaging alone is not the whole answer. Good handling and transport procedures and equipment are also necessary. The selection of a packaging material of sufficient strength and rigidity can reduce damage due to compression loads. Metal, glass and rigid plastic materials may be used for primary or consumer packages. Fibreboard and timber materials are used for secondary or outer packages. The incorporation of cushioning materials into the packaging can protect against impacts, shock and vibration. Corrugated papers and boards, pulpboard and foamed plastics are examples of such cushioning materials. Restricting movement of the product within the package may also reduce damage. This may be achieved by tight-wrapping or shrink-wrapping. Inserts in boxes or cases or thermoformed trays may be used to provide compartments for individual items such as eggs and fruits.
The rate of permeation of water vapour, gases (O2, CO2, N2, ethylene) and volatile odour compounds into or out of the package is an important consideration, in the case of packaging films, laminates and coated papers. Foods with relatively high moisture contents tend to lose water to the atmosphere. This results in a loss of weight and deterioration in appearance and texture. Meat and cheese are typical examples of such foods. Products with relatively low moisture contents will tend to pick up moisture, particularly when exposed to a high humidity atmosphere. Dry powders such as cake mixes and custard powders may cake and lose their free flowing characteristics. Biscuits and snack foods may lose their crispness. If the water activity of a dehydrated product is allowed to rise above a certain critical level, microbiological spoilage may occur. In such cases a packaging material with a low permeability to water vapour, effectively sealed, is required. In contrast, fresh fruit and vegetables continue to respire after harvesting. They use up oxygen and produce water vapour, carbon dioxide and ethylene. As a result, the humidity inside the package increases. If a high humidity develops, condensation may occur within the package when the temperature fluctuates. In such cases, it is necessary to allow for the passage of water vapour out of the package. A packaging material which is semi-permeable to water vapour is required in this case.
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The shelf life of many foods may be extended by creating an atmosphere in the package which is low in oxygen. This can be achieved by vacuum packaging or by replacing the air in the package with carbon dioxide and/or nitrogen. Cheese, cooked and cured meat products, dried meats, egg and coffee powders are examples of such foods. In such cases, the packaging material should have a low permeability to gases and be effectively sealed. This applies also when modified atmosphere packaging (MAP) is used. If a respiring food is sealed in a gastight container, the oxygen will be used up and replaced with carbon dioxide. The rate at which this occurs depends on the rate of respiration of the food, the amount in the package and the temperature. Over a period of time, an anaerobic atmosphere will develop inside the container. If the oxygen content falls below 2%, anaerobic respiration will set in and the food will spoil rapidly. The influence of the level of carbon dioxide in the package varies from product to product. Some fruits and vegetables can tolerate, and may even benefit from, high levels of carbon dioxide while others do not. In such cases, it is necessary to select a packaging material which permits the movement of oxygen into and carbon dioxide out of the package, at a rate which is optimum for the contents. Ethylene is produced by respiring fruits. Even when present in low concentrations, this can accelerate the ripening of the fruit. The packaging material must have an adequate permeability to ethylene to avoid this problem. To retain the pleasant odour associated with many foods, such as coffee, it is necessary to select a packaging material that is a good barrier to the volatile compounds which contribute to that odour. Such materials may also prevent the contents from developing taints due to the absorption of foreign odours. It is worth noting here that films that are good barriers to water vapour may be permeable to volatiles. In those cases where the movement of gases and vapours is to be minimised, metal and glass containers, suitably sealed, may be used. Many flexible film ma- terials, particularly if used in laminates, are also good barriers to vapours and gases. Where some movement of vapours and/or gases is desirable, films that are semi-permeable to them may be used. For products with high respiration rates the packaging material may be perforated. A range of micro-perforated films is available for such applications.
In the case of fatty foods, it is necessary to prevent egress of grease or oil to the outside of the package, where it would spoil its appearance and possibly interfere with the printing and decoration. Greaseproof and parchment papers may give adequate protection to dry fatty foods, such as chocolate and milk powder, while hydrophilic films or laminates are used with wet foods, such as meat or fish.
A package must be able to withstand the changes in temperature which it is likely to encounter, without any reduction in performance or undesirable change in appearance. This is of particular importance when foods are heated or cooled in the package. For many decades metal and glass containers were used for foods which were retorted in the package. It is only in relatively recent times that heat resistant laminates were developed for this purpose. Some packaging films become brittle when exposed to low temperatures and are not suitable for packaging frozen foods. The rate of change of temperature may be important. For example, glass containers have to be heated and cooled slowly to avoid breakage. The method of heating may influence the choice of packaging. Many new packaging materials have been developed for foods which are to be processed or heated by microwaves.
Many food components are sensitive to light, particularly at the blue and ultraviolet end of the spectrum. Vitamins may be destroyed, colours may fade and fats may develop rancidity when exposed to such light waves. The use of packaging materials which are opaque to light will prevent these changes. If it is desirable that the contents be visible, for example to check the clarity of a liquid, coloured materials which filter out short wavelength light may be used. Amber glass bottles, commonly used for beer in the UK, perform this function. Pigmented plastic bottles are used for some health drinks.
Chemical Compatibility of the Packaging Material and the Contents of the Package
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It is essential in food packaging that no health hazard to the consumer should arise as a result of toxic substances, present in the packaging material, leaching into the contents. In the case of flexible packaging films, such substances may be residual monomers from the polymerisation process or additives such as stabilisers, plasticisers, colouring materials etc. To establish the safety of such packaging materials two questions need to be answered: (a) are there any toxic substances present in the packaging material and (b) will they leach into the product? Toxicological testing of just one chemical compound is lengthy, complicated and expensive, usually involving extensive animal feeding trials and requiring expert interpretation of the results. Such undertakings are outside the scope of all but very large food companies. In most countries there are specialist organisations to carry out such this type of investigation, e.g. the British Industrial Biological Research Association (BIBRA) in the UK.
Such work may be commissioned by governments, manufacturers of packaging materials and food companies. To establish the extent of migration of a chemical compound from a packaging material into a food product is also quite complex. The obvious procedure would be to store the food in contact with the packaging material for a specified time under controlled conditions and then to analyse the food to determine the amount of the specific compound present in it. However, detecting a very small amount of a specific compound in a food is a difficult analytical problem. It is now common practice to use simulants instead of real foods for this purpose.
These are liquids or simple solutions which represent different types of foods in migration testing. For example the simulants must follow these specifications [EC (European Commission) specifications]:
Simulant A: distilled water or equivalent (to represent low acid, aqueous foods);
Simulant B: 3% (w/v) acetic acid in aqueous solution (to represent acid foods);
Simulant C: 15% (w/v) ethanol in aqueous solution (to represent foods containing alcohol);
Simulant D: rectified olive oil (to represent fatty foods).
The EC also specifies which simulants are to be used when testing specific foods. More than one simulant may be used with some foods. After been held in contact with the packaging material, under specified conditions, the stimulant is analysed to determine how much of the component under test it contains. Migration testing is seldom carried out by food companies. Specialist organizations mostly do this type of work, e.g. in the UK Pira International.
Most countries have extensive legislation in place controlling the safety of flexible plastic packaging materials for food use. These include limits on the amount of monomer in the packaging material. There is particular concern over the amount of vinyl chloride monomer (VCM) in polyvinylchloride (PVC). The legislation may also include: lists of permitted additives which may be incorporated into different materials, limits on the total migration from the packaging material into the food and limits on the migration of specific substances, such as VCM. The types of simulants to be used in migration tests on different foods and the methods to be used for analysing the simulants may also be specified.
While the discussion above is concerned only with flexible films, other materials used for food packaging may result in undesirable chemicals migrating into foods. These include semirigid and rigid plastic packaging materials, lacquers and sealing compounds used in metal cans, materials used in the closures for glass containers, additives and coatings applied to paper, board and regenerated cellulose films, wood, ceramics and textiles. Apart from causing a health hazard to the consumer, interaction between the packaging material and the food may affect the quality and shelf life of the food and/or the integrity of the package; and it should be avoided. An example of this is the reaction between acid fruits and tinplate cans. This results in the solution of tin in the syrup and the production of hydrogen gas. The appearance of the syrup may deteriorate and coloured fruits may be bleached. In extreme cases, swelling of the can (hydrogen swelling) and even perforation may occur. The solution to this problem is to apply an acid resistant lacquer to the inside of the can. Packaging materials, which are likely to react adversely with the contents, should be avoided, or another barrier substance should be interposed between the packaging material and the food.
Protection Against Microbial Contamination
Another role of the package may be to prevent or limit the contamination of the contents by microorganisms from sources outside the package. This is most important in the case of foods that are heat-sterilised in the package, where it is essential that postprocess contamination does not occur. The metal can has dominated this field for decades and still does. The reliability of the double seam in preventing contamination is one reason for this dominance. Some closures for glass containers are also effective barriers to contamination. It is only in relatively recent times that plastic containers have been developed, which not only withstand the rigours of heat processing, but also whose heat seals are effective in preventing post process contamination. Effective seals are also necessary on cartons, cups and other containers which are aseptically filled with UHT products. The sealing requirements for containers for pasteurized products and foods preserved by drying, freezing, curing, etc. are not so rigorous. However, they should still provide a high level of protection against microbial contamination.
The permeability of the packaging material to gases and the packaging procedure employed can influence the type of microorganisms that grow within the package. Packaging foods in materials that are highly permeable to gases is not likely to bring about any significant change in the microflora, compared to unpackaged foods. However, when a fresh or mildly processed food is packaged in a material that has a low permeability to gases and when an anaerobic atmosphere is created within the package, as a result of respiration of the product or because of vacuum or gas packaging, the type of microorganisms that grow inside the package are likely to be different to those that would grow in the unpackaged food. There is a danger that pathogenic microorganisms could flourish under these conditions and result in food poisoning. Such packaging procedures should not be used without a detailed study of the microbiological implications, taking into account the type of food, the treatment it receives before packaging, the hygienic conditions under which it is packaged and the temperature at which the packaged product is to be stored, transported, displayed in the retail outlet and kept in the home of the consumer.
Protection Against Insect and Rodent Infestation
In temperate climates, moths, beetles and mites are the insects that mainly infest foods. Control of insect infestation is largely a question of good housekeeping. Dry, cool, clean storage conditions, good ventilation, adequate turnaround of warehouse stocks and the controlled use of fumigants or contact insecticides can all help to limit insect infestation. Packaging can also contribute, but an insectproof package is not normally economically feasible, with the exception of metal and glass containers. Some insects are classified as penetrators, as they can gnaw their way through some packaging materials. Paper, paperboard and regenerated cellulose materials offer little resistance to such insects. Packaging films vary in the resistance they offer. In general, the thicker the film the more resistant it is to penetrating insects. Oriented films are usually more resistant that unoriented forms of the same materials. Some laminates, particularly those containing foil, offer good resistance to penetrating insects. Other insects are classified as invaders as they enter through openings in the package. Good design of containers to eliminate as far as possible cracks, crevices and pinholes in corners and seals can limit the ingress of invading insects. The use of adhesive tape to seal any such openings can help. The application of insecticides to some packaging materials is practised to a limited extent, e.g. to the outer layers of multiwall paper sacks. They may be incorporated into adhesives. However, this can only be done if regulations allow it. Packaging does not make a significant contribution to the prevention of infestation by rodents. Only robust metal containers offer resistance to rats and mice. Good, clean storekeeping, provision of barriers to infestation and controlled use of poisons, gassing and trapping are the usual preventive measures taken to limit such infestation.
Many packaging materials contain volatile compounds which give rise to characteristic odours. The contents of a package may become tainted by absorption or solution of such compounds when in direct contact with the packaging materials. Food not in direct contact with the packaging material may absorb odorous compounds present in the free space within the package. Paper, paperboard and fibreboard give off odours which may contaminate food. The cheaper forms of these papers and boards, which contain recycled material, are more likely to cause tainting of the contents. Clay, wax and plastic coatings applied to such materials may also cause tainting. Storage of these packaging materials in clean, dry and well ventilated stores can reduce the problem. Some varieties of wood, such as cedar and cypress, have very strong odours which could contaminate foods. Most polymers are relatively odour-free, but care must be taken in the selection of additives used. Lacquers and sealing compounds used in metal and glass containers are possible sources of odour contamination. Some printing inks and adhesives give off volatile compounds, when drying, which may give rise to tainting of foods. Careful selection of such materials is necessary to lessen the risk of contamination of foods in this way.
There have been many reports in recent years of food packages being deliberately contaminated with toxic substances, metal or glass fragments. The motive for this dangerous practise is often blackmail or revenge against companies. Another less serious, but none the less undesirable activity, is the opening of packages to inspect, or even taste, the contents and returning them to the shelf in the supermarket. This habit is known as grazing. There is no such thing as a tamper-proof package. However, tamper-resistant and/or tamper-evident features can be incorporated into packages. Reclosable glass or plastic bottles and jars are most vulnerable to tampering. Examples of tamper-evident features include: a membrane heat-sealed to the mouth of the container, beneath the cap, roll-on closures, polymer sleeves heat-shrunk over the necks and caps, breakable caps which are connected to a band by means of frangible bridges that break when the cap is opened and leave the band on the neck of the container.
There are many other factors to be considered when selecting a package for a particular duty. The package must have a size and shape which makes it easy to handle, store and display on the supermarket shelf. Equipment must be available to form, fill and seal the containers at an acceptable speed and with an adequately low failure rate. The package must be aesthetically compatible with the contents. For example, the consumer tends to associate a particular type of package with a given food or drink. Good quality wines are packaged in glass, whereas cheaper ones may be packaged in 'bag in box' containers or plastic bottles. The decoration on the package must be attractive. A look around a supermarket confirms the role of the well designed package in attracting the consumer to purchase that product. The labelling must clearly convey all the information required to the consumer and comply with relevant regulations. Detailed discussion of these factors is not included in this chapter but further information is available in the literature.
MODIFIED ATMOSPHERIC PACKAGING (MAP)
Carbon dioxide (CO2) is a colourless gas with a slight pungent odour at very high concentrations and is an asphyxiant and slightly corrosive in the presence of moisture.
CO2 dissolves readily in water to produce carbonic acid (H2CO3) that increases the acidity of the solution and reduces the pH.
This gas is also soluble in lipids and some other organic compounds. The solubility of CO2 increases with decreasing temperature. For this reason, the antimicrobial activity of CO2 is markedly greater at temperatures below 10°C than at 15°C or higher.
The high solubility of CO2 can result in pack collapse due to the reduction of headspace volume. In some MAP applications, pack collapse is favoured, for example in flow wrapped cheese for retail sale.
Oxygen (O2) is a colourless, odourless gas that is highly reactive and supports combustion. Oxygen promotes several types of deteriorative reactions in foods including fat oxidation, browning reactions and pigment oxidation.
Most of the common spoilage bacteria and fungi require O2 for growth. Therefore, to increase the shelf life of foods, the pack atmosphere should contain a low concentration of residual O2.
It should be noted that in some foods a low concentration of O2 can result in quality and safety problems (for example, unfavourable colour changes in red meat pigments, senescence in fruits and vegetables and growth of food poisoning bacteria), and this must be taken into account when selecting the gaseous composition for a packaged food.
Nitrogen (N2) is a relatively un-reactive gas with no odour, taste or colour.
Nitrogen does not support the growth of aerobic microbes and therefore inhibits the growth of aerobic spoilage but does not prevent the growth of anaerobic bacteria.
The low solubility of N2 in foods can be used to prevent pack collapse by including sufficient N2 in the gas mix to balance the volume decrease due to CO2 going into solution.
Carbon monoxide (CO) is a colourless, tasteless and odourless gas that is highly reactive and very flammable. It has a low solubility in water but is relatively soluble in some organic solvents.
CO has been studied in the MAP of meat and has been licensed for use in the USA to prevent browning in packed lettuce.
Commercial application has been limited because of its toxicity and the formation of potentially explosive mixtures with air.
The noble gases are a family of elements characterised by their lack of reactivity and include helium (He), argon (Ar), xenon (Xe) and neon (Ne).
These gases are being used in a number of food applications now, e.g. potato-based snack products.
While from a scientific perspective it is difficult to see how the use of noble gases would offer any preservation advantages compared with N2 they are nevertheless being used. This would suggest that there may be, as yet unpublished, advantages for their use.
UHT-treated products have to be packaged under conditions which prevent microbiological contamination, i.e. aseptically packaged. With some high-acid foods (pH<4.5), it may be sufficient to cool the product after UHT treatment to just below 100°C, fill it into a clean container, seal the container and hold it at that temperature for some minutes before cooling it. This procedure will inactivate microorganisms that may have been in the container or entered during the filling operation and which might grow in the product. The filled container may need to be inverted for some or all of the holding period. However, in the case of low-acid foods (pH>4.5) this procedure would not be adequate to ensure the sterility of the product. Consequently for such products, aseptic filling must involve sterilising the empty container or the material from which the container is made, filling it with the UHT-treated product and sealing it without it being contaminated with microorganisms.
In the case of rigid metal containers, superheated steam may be used to sterilize the empty containers and maintain a sterile atmosphere during the filling and sealing operations. Empty cans are carried on a stainless steel conveyor through a stainless steel tunnel. Superheated steam, at a temperature of approximately 260°C, is introduced into the tunnel to sterilise the cans. They then move into an enclosed filling section, maintained sterile by superheated steam. They are sprayed on the outside with cool sterile water before being filled with the cooled UHT product. The filled cans move into an enclosed seaming section, which is also maintained in a sterile condition with superheated steam. The can ends are also sterilised with superheated steam and double-seamed onto the filled cans in the sterile seaming section. The filled and seamed cans then exit from the tunnel. The whole system has to be presterilised and the temperatures adjusted to the appropriate levels before filling commences. This aseptic filling procedure is known as the Dole process. Glass containers and some plastic and composite containers may be aseptically filled by this method.
Cartons made from a laminate of paper/aluminium foil/polyethylene are widely used for UHT products such as liquid milk and fruit juices. This type of packaging material cannot be sterilised by heat alone. A combination of heat and chemical sterilant is used. Treatments with hydrogen peroxide, peracetic acid, ethylene oxide, ionising radiation, ultraviolet radiation and sterile air have all been investigated. Hydrogen peroxide at a concentration of 35% in water and 90°C is very effective against heat-resistant, sporeforming microorganisms and is widely used commercially as a sterilant in aseptic packaging in laminates. Form-fill-seal systems are available, an example being the Tetra Brik system, offered by Tetra Pak Ltd (Fig 1).
Figure 1: Principle of the Tetra Brik aseptic packaging system (adapted from: Food Processing Handbook)
The packaging material, a polyethylene/paper/polyethylene/foil/polyethylene laminate, is unwound from a reel and a plastic strip is attached to one edge, which will eventually overlap the internal longitudinal seal in the carton (1). It then passes through a deep bath of hot hydrogen peroxide, which wets the laminate. As it emerges from the bath, the laminate passes between squeeze rollers, which express liquid hydrogen peroxide for return to the bath (2). Next, a high-velocity jet of hot sterile air is directed onto both sides of the laminate to remove residual hydrogen peroxide, as a vapour. The laminate, which is now sterile and dry, is formed into a tube with a longitudinal seal in an enclosed section which is maintained sterile by means of hot, sterile air under pressure (3). The product filling tube is located down the centre of the laminate tube. The presterilised product is fed into the sterile zone near the bottom of the tube, which is heatsealed. The air containing the vaporised hydrogen peroxide is collected in a cover and directed to a compressor where it is mixed with water, which washes out the residual hydrogen peroxide. The air is sterilised by heat and returned to the filling zone. In another system, the laminate is in the form of carton blanks which are erected and then sterilised by a downward spray of hydrogen peroxide followed by hot sterile air. This completes the sterilisation and removes residual hydrogen peroxide. The presterilised product is filled into the cartons and the top sealed within a sterile zone. Similar systems are available to aseptically fill into preformed plastic cups. The lidding material is sterilised with hydrogen peroxide or infrared radiation before being heat-sealed onto the cups within a sterile zone. Thermoform filling systems are available to aseptically fill into polymer laminates. The web of laminate passes through a bath of hydrogen peroxide and then is contacted by hot sterile air which completes the sterilisation, removes residual hydrogen peroxide and softens the laminate. The laminate is then thermoformed into cups and filled with presterilised product within a sterile zone. The sterilised lidding material is applied before the cups leave the sterile zone. Thermoforming systems are usually used to fill small containers e.g. for individual portions of milk, cream and whiteners.
Oxygen can have considerable detrimental effects on foods.
Oxygen scavengers can therefore help maintain food product quality by decreasing food metabolism, reducing oxidative rancidity, inhibiting undesirable oxidation of labile pigments and vitamins, controlling enzymic discolouration and inhibiting the growth of aerobic microorganisms
Carbon dioxide scavengers/emitters
The use of carbon dioxide scavengers is particularly applicable for fresh roasted or ground coffees that produce significant volumes of carbon dioxide.
Fresh roasted or ground coffees cannot be left unpackaged since they will absorb moisture and oxygen and lose desirable volatile aromas and flavours.
However, if coffee is hermetically sealed in packs directly after roasting, the carbon dioxide released will build up within the packs and eventually cause them to burst
To circumvent this problem, two solutions are currently used. The first is to use packaging with patented one-way valves that will allow excess carbon dioxide to escape. The second solution is to use a carbon dioxide scavenger or a dual-action oxygen and carbon dioxide scavenger system.
Ethylene (C2H4) is a plant growth regulator which accelerates the respiration rate and subsequent senescence of horticultural products such as fruit, vegetables and flowers.
Many of the effects of ethylene are necessary, e.g. induction of flowering in pineapples, colour development in citrus fruits, bananas and tomatoes, stimulation of root production in baby carrots and development of bitter flavour in bulk delivered cucumbers, but in most horticultural situations it is desirable to remove ethylene or to suppress its negative effects.
Activated carbon-based scavengers with various metal catalysts can also effectively remove ethylene.
The use of ethanol as an antimicrobial agent is well documented.
It is particularly effective against mould but can also inhibit the growth of yeasts and bacteria. Ethanol can be sprayed directly onto food products just prior to packaging.
However, a more practical and safer method of generating ethanol is through the use of ethanol-emitting films and sachets
Antimicrobial and antioxidant packaging films which have preservative properties for extending the shelf life of a wide range of food products
For example, one widely reported product is a synthetic silver zeolite which has been directly incorporated into food contact packaging film.
The purpose of the zeolite is, apparently, to allow slow release of antimicrobial silver ions into the surface of food products.
The major potential food applications for antimicrobial films include meats, fish, bread, cheese, fruit and vegetables.
Excess moisture is a major cause of food spoilage.
Soaking up moisture by using various absorbers or desiccants is very effective in maintaining food quality and extending shelf life by inhibiting microbial growth and moisture related degradation of texture and flavour.
Several companies manufacture moisture absorbers in the form of sachets, pads, sheets or blankets.
For dual-action purposes, these sachets may also contain activated carbon for odour adsorption or iron powder for oxygen scavenging
The interaction of packaging with food flavours and aromas has long been recognised, especially through the undesirable flavour scalping of desirable food components.
Commercially, very few active packaging techniques have been used to selectively remove undesirable flavours and taints, but many potential opportunities exist.
An example of such an opportunity is the debittering of pasteurised orange juices (caused by limonin).
Processes have been developed for debittering such juices by passing them through columns of cellulose triacetate or nylon beads.
A possible active-packaging solution would be to include limonin adsorbers (e.g. cellulose triacetate or acetylated paper) into orange juice packaging material.
Temperature control packaging
Temperature control active packaging includes the use of innovative insulating materials, self-heating and self-cooling cans.
For example, to guard against undue temperature abuse during storage and distribution of chilled foods, special insulating materials have been developed.