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Barrier Properties Of Films 03 12



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Barrier Properties Of Films 03 12

  1. 1. BARRIER PROPERTIES of FILMS current technology & applications Henky Wibawa AMCOR FLEXIBLES INDONESIA Technical Director March 2012
  2. 2. Introduction
  3. 3. Introduction The primary functions of packaging are containment, protection, information and convenience. Probably the most basic function of a packaging is to contain its filling good. Milk, loose peas or potato chips would have a hard time finding its way to the consumer without retail packaging. Protection is often considered as the most important functionality of the package. Shielding the food from the attack of animals (mice, insects etc.), micro-organisms, impede its contamination with dust, dirt or chemicals, resist the impact of shocks, vibrations or compressive forces and guarding the filling good from the adverse effects of too much or too little moisture, light or oxygen is the ‘raison d’être ‘ of the package.
  4. 4. Introduction Packaging at the POS/POP
  5. 5. Packaging Materials
  6. 6. Aluminium Foils Aluminium foil is essentially impermeable to gasses and water vapour above a thickness of approx. 20 microns. For thinner gauges one can detect a small but non-zero permeability due to pinholes (e.g. a 7mm foil has a water vapour transmissions rate (WVTR) of approx. 0.2 g /m² *day at 38°C and 90 % rel, humidity and a O2 transmission rate of 0.1-0.2 ml /m2*day*bar). Aluminium foil exhibits desirable deadfold characteristics ; i.e. when wrapped around an object, it will assume its profile with no springback (e.g. butter wrapper). Typical applications are in coffee packaging (PET/Al/LDPE), medical and consumer health care packaging (hard annealed Al foil for blisters, sachets), dry soups (BOPP/Al/LDPE) or lidding material for ready meals (PET/Al/PP) and dairy products (heat seal lacquered foil).
  7. 7. Biaxially Oriented Polypropylene With 0.9 g/m³, BOPP has the lowest density of the common packaging materials. Its melting point lies with 169 °C high enough to allow for sterilisation applications. BOPP prominent qualities are: excellent moisture barrier, toughness, clarity and low cost. Low tear resistance make it suitable for easy-open applications. Some of the disadvantages (low gas and aroma barrier, poor sealabilty, printability and maschinability) are surmounted by co-extrusion or coatings: Co-extrusion with PP-PE co-polymer sealability Acrylate coating increased gloss, printability and machinability PVDC coating increased gas and aroma barrier, sealability PVOH oxygen barrier, printability Metallisation oxygen, aroma, moisture and light barrier BOPP can also be produces in an opaque variety either by filling with white particles or by cavitation. This latter method leads to pearlised, light weight material with low light transmission and high gloss. The combination of the above mentioned variables leads to a broad spectrum of possible applications in food packaging. Main applications are chocolate bars, biscuits, snacks, ice cream, sweets etc.
  8. 8. Biaxially Oriented Polyester Polyethyleneterephthalate has density of 1.40 g/m3 and a melting point of 260°C. PET films are almost exclusively used in the bi- oriented, heat stabilised form. PET posses outstanding tear resistance, high transparency and gloss as well as remarkable resistance to scratching and abrasion. In addition its excellent printability combined with an advantageous machinability and dimensional stability makes it one of the converters preferred materials. PET can be used a temperature range of –50 °C to +150°C. It exhibits good barrier properties with respect to water vapour, gases and fats. Typical examples where PET is used are PET/AL/LDPE (coffee pouches, medical sachets), PET met./LDPE (snacks, coffee, biscuits) or PET/Al/PP as peelable, sterilisable lidding material for ready meals. PET is furthermore the prevailing substrate for special barrier layers. The most common one is certainly the metallisation. Others include clay platelets, SiOx and PVDC. They will be discussed further on.
  9. 9. Biaxially Oriented Polyamide The denomination polyamide refers to whole family of polymer. Nylon (PA-6) is produced by a ring opening reaction of e-caprolactam, a molecule that already contains the amid group in its initial structure. The most widespread polyamides in flexible packaging are PA 6 and PA 6-6 with a density of 1.13 and a melting point of 220 °C, allowing for 140°C sterilisation procedures. Nylon films are characterised by high impact resistance and high tensile strength. They exhibit good stiffness and are resistant to fats, oils, dilute bases and acids. Their barrier with respect to gases is very good in dry conditions, but deteriorates rapidly with increasing humidity. Water vapour transmission rate is quite high and increases with rising moisture content of the material. BOPA are produced showing up to threefold improved tear resistance, increased impact strength, improved optical properties and higher barrier values. The main applications of polyamides are to be found in the field of MAP/ vacuum packaging of cured meat and cheese products (OPA/PE).
  10. 10. EVOH Ethylene-vinyl alcohol resins are hydrolysed co-polymers of ethylene and vinylacetate. The resulting structure combines the excellent gas barrier properties of vinyl alcohol and the chemical resistance and processability of polyethylene. EVOH exhibits under dry conditions an exceptional gas barrier. Under the influence of humidity, these barrier properties deteriorate however dramatically. This is due to the fact that EVOH contains large amounts of hydrophilic hydroxy groups, which readily interact with water. EVOH films are usually embedded in polyolefin layers with a good water barrier. EVOH resins are highly crystalline, thermally stable, have high mechanical strength, elasticity and surface hardness, very high gloss, low haze, good abrasion resistance, very high resistance to oils and organic solvents, and provide an excellent barrier to odours. EVOH multi-layer materials are often employed in modified atmosphere packaging of ready meals, cured meat, bakery products or fresh pasta. (PE/EVOH/PE or PA/EVOH/PE for lidding PS/EVOH/PE for tray material).
  11. 11. PVdC Vinylidene chloride is usually co-polymerised with vinyl chloride (typically 20%) to yield a soft, tough and relatively impermeable film. It is an especially heavy polymer (density 1.68 – 1.75 g/m3). Pure PVdC results in a stiff, brittle film hardly suitable for packaging purposes. Co-polymers of PVdC show a unique combination of low water vapour transmission rate and oxygen permeability (SARAN® 25 m: WVTR 2.4 g/m2*day (38°C/90%RH), O2 -TR: 16 ml/m2*day*bar (23°C/50%RH)). PVdC lattices are very often applied as aqueous dispersion to paper and plastics films to provide barrier to gases and moisture and odours. It provides furthermore a reasonable sealability to any substrate. Typical applications are medical blister (PVC 250 m / 40 g/m2 PVDC) or biscuit wrapping (PAP 60 g/m2 / PVDC 20 g/m2).
  12. 12. BAREX BAREX is a tradename for rubber-modified co-polymers of acrylonitrile and methyl acrylate. They were originally developed for beverage bottle usage because of their excellent barrier properties, clarity, high impact strength and insolubility in many organic solvents. In flexible packaging its outstanding resistance to oils, fats and aggressive products are appreciated. It replaces polyethylene as a sealant in cases where the product is too aggressive to be in direct contact with polyolefins. In laminates with paper/aluminium foil/BAREX it is frequently used in form of sachets for packaging soups, spices, aromas, perfumes or lemon juice.
  13. 13. Coated materials: metallising Metallised film is developed by vapourising molten metal, and depositing it onto a cold polymer web. Aluminium is most commonly used because of its cost-effectiveness. The process takes place in a vacuum chamber; the amount of metal applied is carefully controlled by instrumentation, and the vacuum temperature of the metal and speed of the web feed must also be closely monitored. The thickness of the deposited layer is approximately 30 nm. Metallisation improves the moisture- and gas-barrier properties of the film and prevents light from reaching the product. It also confers the material a glossy metal appearance. It is therefore also used for decorative purposes e.g. in the confectionery market segment. The two most common substrates are PET and OPP. HDPE and OPA are less frequently metallised. Applications are very wide spread in packaging of water- and oxygen sensitive filling goods
  14. 14. Raw materials - Barrier films Vacuum coated films Metallization process THE KEY PARAMETERS OF THE METALLIZING PROCESS ARE: •stable vacuum for even and consistent coating; •temperature control to avoid deformation and damage to the material; •accurate winding control especially on the low tension range.
  15. 15. Coated materials: SiOx, AlOx As an alternative to Al-metallisation transparent barrier layers can be employed. The so-called glassy barrier layers consist of amorphous metal oxides of approx. 30 nm thickness. In practise only two play a significant role, namely silicon oxide (SiOx) and aluminium oxide (Al2O3) layers. Three different methods of deposition exist: Thermal evaporation of SiO, electron beam induced evaporation of SiO/SiO2 and Plasma enhanced chemical vapour deposition. Main applications are packaging of oxygen/ moisture sensitive foods in areas where it is desirable to see the product (transparent barrier). Substrates are mainly PET but also to some extend OPP. Both are microwaveable. When the fragile and rather brittle glassy layer is protected by an additional layer, the structure becomes retortable. Another target market is the replacement of triple structures such as PET/Al/PE by duplex structures such as PET-SiOx/PE. Yet another method to create a thin transparent layer is to apply an organic lacquer with dispersed clay platelets, creating a tortuous path for gases, organic solvents, aromas and UV light. This trick leads to a high barrier material with a WVTR of about 25g/m²*day and an oxygen permeability of < 1cm3/m²*day (23°C/85%RH).
  16. 16. Low density polyethylene and derivatives PE is the largest volume single polymer used in food packaging. The way in which the gaseous monomer ethylene is polymerised determines to large extend the density and the properties of the final product. The crystallinity of low density polyethylene LDPE usually varies between 50 – 70 % and its density between 0.915 – 0.935 g/cm3. The softening point of LDPE is just below 100°C thus precluding its utilisation in sterilisation applications. LDPE is tough, with good tensile strength, impact and tear resistance and posses an exceptional barrier to water. The permeability for oxygen and other gases is however very high. It has very good chemical resistance to acids, alkalis but is sensitive to hydrocarbons, oils and greases. Oils and many other organic compounds including many aromas are absorbed by LDPE leading to swelling of the polymer. The most outstanding property of LDPE is its ability to be fusion welded to itself to yield good, tough, liquid tight seals. LLDPEs can be produced in wide range of densities ranging from 0.90 to 0.935 g/cm3. A mayor feature of LLDPE is that its molecular weight distribution is narrower than that of LDPE leading to a an improved chemical resistance, tear resistance and impact strength, higher surface gloss, and higher melting point.
  17. 17. Ionomers With density 0.94g/cm3 are co-polymers of ethylene and a small amount of an unsaturated short chain carboxylic acid (e.g. methacrylic acid). The resulting polymer is than neutralised to varying degrees with metal derivatives (e.g. zinc acetate) leading to an ionisation of the carboxylic acid groups. As a consequence ionic cross-linking occurs between different branches of the polymer leading to enhanced stiffness and toughness. In comparison with LDPE ionomers have an improved oil and grease resistance, which particularly appreciated when sealing packages with oily or greasy contents, as it allows for correct sealing even through fat contaminated sealing areas. Ionomers also exhibit increased clarity and abrasion resistance with respect to LDPEs. The moisture barrier is however reduced due to a lower degree of crystallinity. The most prevalent trade name for ionomers is Surlyn® by DuPont. The two captions currently used are sodium and zinc. The former has a better hot tack and better fat resistance while the latter results in a better adherence to aluminium and metallised surfaces. A typical application is in combination with polyamide for MAP/vacuum packaging of meat and poultry and cheese products.
  18. 18. More polymers
  19. 19. Packaging Industries Can Take Advantage of Innovative Technology. New Microwave Packaging Concepts Active Packaging Concepts Reactive coatings (micro contact inks, polymer electronics etc.) Digital print technologies/ Ink jet Barrier packaging Variable labels & labeling Package security features Nanotechnology
  20. 20. Transport Properties
  21. 21. WVTR The water vapour transmission (WVTR) rate of a packaging material depends on two mayor factors: the permeation rate through the material and the difference in water vapour pressure in- and outside the package (the chemical potential gradient, Dm). To give an example , the water vapour pressure at 23°C, 85% rel. humidity is 23,5 mbar is only about a third of that at 38°C and 90% rel. humidity (72,6 mbar). The permeation rate is again a function of two mayor factors: the solubility of water in the polymer and its diffusion coefficient (P = D x S. The solubility of water depends on the interaction between the polar water molecule and the polymer molecular structure. The more polar groups the polymer contains, the higher the enthalpy of solution and the higher the solubility. The diffusion depends on the degree of crystallinity and on the moisture content of the polymer. The higher the crystallinity, the lower the diffusion speed is. The moisture content has two opposing effects on the diffusion process. On the other hand does interaction with the polymer bind the water reducing its mobility. The temperature dependence is thus expressed in the form. WVTR also depends on the thickness of the relevant material. It is often assumed to be a linear relationship.
  22. 22. Gas permeability For ambient gases other than water vapour the same is true as for the above mentioned WVTR except that the solubility is to a much lesser degree dependent on the nature of the polymer. It turns out that the permeability ratio of a pair of gases will be relatively constant over a series of polymers. The ratios of the permeabilities of CO2 to N2 vary only by a factor of approx. 2 whereas the individual film permeabilities exhibit a factor of up to 500. It can also be seen that independent of the film material oxygen permeates about six times as fast as nitrogen and CO2 about four times as fast as oxygen and about 24 times as fast as nitrogen. There is no pattern for the ratios of water vapour to any of the three gases. It might seem strange that CO2, the largest of the three gas molecules, has the highest permeability coefficient. Some of the factors influencing the permeability of polymers are : the chemical nature of the polymer (polymer – permeant interaction) microstructure of the polymer – crystallinity, thickness of the film, temperature, relative humidity (swelling, plasticising), and other volatile compounds (such as solvents) which lead to swelling additional layers such as metallisation, SiOx, Ormoceres®, CHx, diamond-like layers, clay platelets, PVdC or others.
  23. 23. Raw materials - Plastics Barrier films Material Characteristic O.D. µm O2 TR WV TR 2 cc/m *24h g/m2*24h PET Standard PET / 12 110 50 23°C 0% RH 38°C 90% RH PET PVDC coated / 12 8 8 23°C 85% RH 38°C 90% RH PET SiOx coated / 12 3.5 39 23°C 85% RH 38°C 90% RH PET Al2O3 coated / 12 2 2 23°C 0% RH 38°C 90% RH PET metallised 2.0 12 1.5 1.5 23°C 75% RH 38°C 90% RH PET white and metallised 2.2 12 1.5 1.5 23°C 75% RH 38°C 90% RH PET with inorganic coating / 12 1 25 23°C 60% RH 38°C 90% RH PET metallised very high barrier 2.6 12 0.08 0.04 25°C 85% RH 38°C 90% RH PEN Polyethylen naphtalate / 19 <1 3.8 38°C 90% RH PAN Polyacrilonitrile / 0.8 5 23°C 75% RH 38°C 90% RH
  24. 24. Raw materials - Plastics Barrier films M aterial Characteristic O.D. µm O 2 TR W V TR cc/m 2 *24h g/m2*24h BOPP Standard bioriented PP / 20 2000 7.5 23°C 0% RH 38 °C 90% RH BOPP Acrylic coated / 26 750 5 23°C 0% RH 38°C 90% RH BOPP PVdC coated / 26 25 4.2 23°C 0% RH 38°C 90% RH BOPP metallized 2.3 20 100 0.7 23°C 0% RH 38°C 90% RH BOPP cavitated and metallized 2.4 40 130 2 23°C 0% RH 38°C 90% RH BOPP metallised high barrier 2.2 16 30 1.5 23°C 0% RH 38°C 90% RH BOPP PVOH coated / 25 3 5 23°C 0% RH 38°C 90% RH BOPP metallized very high barrier ? 18 0.5 0.3 23°C 0% RH 38°C 90% RH BOPP cavitated - metallized very high barrier 3.6 35 0.2 0.4 23°C 0% RH 38 °C 90% RH OPA Standard oriented polyamide / 15 30 180 23°C 0% RH 38 °C 90% RH PA PA - EVOH - PA / 10 evoh 0.5 180 23°C 0% RH 38°C 90% RH PP PP - EVOH - PP / 15 evoh 0.3 100 23°C 0% RH 38°C 90% RH PE PE - EVOH - PE / 15 evoh / 130 38°C 90% RH
  25. 25. Seal Sealing has a decisive influence on the whole package permeability, the factor that in the end determines the total amount of oxygen or gas that enters or leaves the package. Whatever you again with a high barrier layer you might loose by improper sealing. Replacing a laminate PET/Al/PE-LD with a structure OPP (high barrier) / OPP coex. without adjusting the packaging machine might lead to a flawed seal. The second problem with the seal is the drainage effect; if the barrier layer is not close enough to the filling good. In this case oxygen and /or water might diffuse via the cutting edge of the seal along the more permeable layer towards the filling good without having to pass the barrier. An example of such a packaging material was the structure (from outside to inside) : OPP 20mm / Al 12 mm / Paper 40 g /m²/wax which was used for packaging Ritter Sport Chocolate for a long time.
  26. 26. Converting of packaging materials
  27. 27. Converting Procedure Photos Scanning for Colour Separation Cylinder Customer Design & Engraving Concept Artwork Flexo Text Composing Sleeves (Text + Images) C o n v e r t i n g Metallising Waxing /Coating (Co) Extrusion Lamination Printing -adhesives - inks / - primers -lacquers - aluminium - resins - primers film/ foil/ paper - paraffins - film/ foil/ paper - solvents Slitting Die Cutting Bag-Making
  28. 28. Extrusion Extruders consist of barrel, screw, drive mechanisms and control. The solid polymer is fed into the extruder as powder, flakes or pellets and then melted and mixed by being passed through an Archimedean screw. The shear friction of the pellets between each other and to the machine causes heating of the polymer, which finally leads to melting. The extruder is heated additionally in various zones to be able to control the temperature distribution, but this heating itself does not effect the melting of the solid polymer. The polymer melt temperature depends mainly on the rotation speed of the screw, the demanded output and the pressure of the polymer melt at the outlet filter. Extrusion can also be used for coating with polymer blends, the extruder then requires different feeder stations. Because food packaging can require a wide range of properties, two or more polymers are often coextruded through a single die to form a multi- layer film structure. Coextrusion is recommended for producing multi- layer films because of its lower cost; it can be used instead of lamination, avoiding the problem of double handling that occurs when a film lamination is being produced. Coextrusion is sometimes preferred because laminations require a separate manufacturing process for each film used in the final laminate.
  29. 29. Lamination A lamination is created when two or more individual films are bonded together with special adhesives and run through rolling, heated cylinders to produce a composite film structure. One talks about wet bond laminating when the adhesive is wet in the moment of joining of the two webs, whereas dry bonding lamination is effected when the adhesive is dried before bonding. In the case of wet bond laminating one of the webs has to be permeable to the solvent (e.g. water based casein glue used to laminate paper and aluminium foil). Solvent-based adhesives are very often two component polyurethane – isocyanate systems with ethylacetate as the principal solvent. Curing occurs after lamination during the following few days. Solvent-free adhesive systems are usually based on short chain precursor polymers e.g. oligourethanes which serve as their own solvent and a curing agent. Lamination is preferred when a specific film composition cannot be effectively run on coextrusion systems due to equipment limitations, and also when the high temperatures required in coextrusion would be harmful to films. Lamination is also recommended when it is desirable to produce a composite film with properties superior to those afforded by a single film layer of the same gauge.
  30. 30. Lamination Arrangements n roller arrangements for different types of lamination 1. Wax lamination 2. Wet lamination 3. Solvent-free lamination 4. Dry lamination 5. Dry lamination uncoated web coated web laminate
  31. 31. Coating The coating process involves the application of various materials to the film-web substrate to special features, improve properties, or change the handling characteristics (sticking, slipping, etc.) of a film. Two main families of coating exist: protective coatings (overlacquer) and coatings with a sealing function. The former have to be hard, scratch resistant and thermally stable (e.g. NC-, epoxy- or PET-based systems), the latter have to be flexible, tight, chemically resistant and sealable (eg.g EVA-, PVA-, PVC- or PVDC-based systems). In practise a hole panoply of different resins, additives and solvents exists from which the converter can choose to find the right combination for each individual application. Coating equipment consists of a coating head, often an engraved rotogravure cylinder, a drying unit, and the film- handling system.
  32. 32. Printing Printing is one important step in producing a package material. The choice of the printing technique and inks will to a large extend influence on the visual and sensory (off-flavours, rest solvents) quality of the final material. Two different methods are commonly employed in flexible packaging : Rotogravure printing technique commonly used in packaging. Printing can be performed on foil, film and paper/carton. Rotogravure machines usually range between 6 to 12 colours. Printing speed is 100- 300m/min. In rotogravure an engraved cylinder is rotating partially within the printing ink, where its indentions are filled with the respective ink. Excess ink is removed by a doctor blade. The ink from the indentions is then transferred onto the substrate, which is pressed to the rotogravure cylinder by a second press cylinder. The quality of the print is very high, but set-up of the printing machine takes approximately 10min per colour. Flexo printing is the second standard printing method in packaging. Printing plates are mounted to a cylinder, which then transfers the ink from a cylinder dipping into the ink reservoir to the substrate with nearly no pressure applied. Set-up times are somewhat shorter than for rotogravure. Also available with UV curing inks as UV Flexo.
  33. 33. Snacks example ... what are on the market?
  34. 34. Packaging machines and gas flushing
  35. 35. Application and control Packaging line and material performances
  36. 36. Pillow packs The HFFS is employed for the making of pillow packs. A tube is formed from hot or cold sealable wrapping film by means of an unwinder and corresponding turning system. The product slugs, in an exactly defined interval, are then inserted into this tube means of an in-feed chain (Fig. 3a). The tube is then sealed along its length. In order to firmly seal the package ends, it is passed through a cross-sealing station (Fig. 3b). Thanks to our unique cross sealing technology, a tight seam is created between the portioned slugs. Cutting occurs simultaneously. The result: A pillow pack characterised by the typical “end fins".
  37. 37. Flat bottom pouches Vertical bag formation: The bags are manufactured by forming a pack around a vertical moulded tube. The passage over the form-giving shoulder is the critical step in the making of the pouch as it imposes considerable mechanical strain on the packaging material. The so-formed tubular pack is then sealed lengthways. At the end of the moulded tube, the pack is sealed along the bottom and the individuals are separated. This yields an open-top bag is then conveyed to the cup filler of the packaging system. There are also variations where filling occurs directly from the moulded tube.
  38. 38. Coffee vacuum packaging Manufacturing a bag on the mandrel wheel is a unique procedure. Firstly, for each paper or film section fed from the reel stack is precisely positioned and placed around one of the metal mandrels the mandrel wheel. The intermittently mandrel wheel now conveys the so formed package cases to further stations at which the bottom and side seams are created sealed to yield neatly formed bags left open at the top. These are then transferred to the cup filler of the packaging system. After they have been filled, the bags closed and sealed at the top. Depending on the product and the customer requirements, various seals are possible. Evacuation vacuum wheel with up to 30 chambers gas flushing also number among the possible designs.
  39. 39. Product sensitivity-food deteroriation mechanism Factors that influence shelf-life are basically to be classified into three areas: Food properties, package properties and climatic storage condition. The former have been treated previously, the latter clearly affect the kinetics of the shelf-life determining process of food degradation in multiple ways. Foods are complex blends of often hundreds of different compounds. Their chemical and physical properties determine they sensitivity with respect to inevitable degradation. Here it gives an overview of the principal factors influencing the degradation of foods.
  40. 40. Physical Bruising and mechanical deterioration of products is of principal concern to food producers and packaging engineers. Examples are physical abuse of fruits or vegetables during packaging or distribution or crushing of biscuits or chips. Temperature induced texture changes are usually the result of phase changes. Examples are sugar and fat bloom as a case of re- crystallisation and phase segregation respectively. Freezer burn constitutes an example of water sublimation and temperature fluctuations around the dew point may lead to unwanted condensation of water in the package. Flavour scalping The absorption of flavour and aroma compounds by the packing materials inner liner is on of the most important problems of compatibility in flexible packaging]. The most prominent example is certainly the case of fruit juice in contact with polyolefin sealing layers.
  41. 41. Physical Moisture gain or loss can alter considerably the texture of foods. Intermediate moisture foods such as pet food or cakes may harden due to an excessive loss of humidity. Pasta turns brittle when it changes from the rubbery to the glassy state and inversely snacks such as potato chips or curls turn soggy when they move in the inverse direction. Caking is yet another example where the increase of moisture and temperature induce a glass – rubbery transition leading to the agglomeration in powdery products. The sorption behaviour of foods is quantified with the aid of so-called water absorption isotherms. They put into relation the amount of absorbed water (moisture in g/g dry solid) with the relative ambient humidity. This is true for a specific temperature, hence the term isotherm and after an equilibrium state has been reached. A typical water absorption isotherm of a biscuit is shown in aw stands for water activity which relates to the relative humidity RH like RH = 100*aw.
  42. 42. Chemical During processing and storage of food stuffs a great variety of chemical reactions can alter the food chemical composition and lead to degradation in terms of nutritive value or organoleptic properties. The mayor modes are mentioned below: Enzymatic During processing of foods, tissue damage occurs which causes the release of various chemical constituents into the cellular fluid. These chemicals can then react with each other or with compounds from the environment. For example lipoxidase enzymes released from certain cell constituents (mitochondria) can attack fats and cause rancidity. Similarly, the polyphenol oxidase can react with some parts of the cell and oxygen to form the well known brown colour of bruised or cut fruit (e.g. apples or bananas). Lipid oxidation Many foods contain unsaturated fats, which are important for human nutrition. Unfortunately, these fats are subject to direct attack by oxygen through an auto-catalytic free radical mechanism. This results in rancid off-flavours which render the food undesirable to consume. Very little fat has to oxidise for the consumer to detect rancidity and reject the food. Light and trace metals can under certain circumstances catalyse the reaction rate by orders of magnitude.
  43. 43. Chemical Nonenzymatic Browning (NEB) NEB stands for another mayor family of chemical reactions leading to a loss of nutritional and organoleptic value of the affected food. NEB is the result of reactions between reducing sugars such as glucose, fructose or lactose and amino group containing compounds such as proteins. Browning can also occur by heating sugars to high temperatures (or very long reaction times) or through the oxidation of vitamin C. Undesirable aspects of NEB are the production of bitter flavours, darkening of light-coloured dry products such as infant formulae or juices and the staling of coffee. Factors which influence the rate of NEB are temperature, water activity and acidity (pH). Moisture Moisture changes may induce food deterioration by physical means (see above) or chemical means. All the above mentioned modes of deterioration enzymatic, lipid oxidation, NEB and also microbial growth are strongly affected by water. The rates at which these reactions take place depend markedly on the water activity of the food. One also has to take into consideration that water activity rather than total moisture content is the relevant parameter determining undesired chemical changes in foods.
  44. 44. Microbial Micro-organisms constitute an important mechanism by which many foods, especially fresh ones , lose their quality. This is because microbes are ubiquitous in the environment and grow very fast. Knowledge of the rate of growth of microbes as a function of the environmental conditions is very essential in the prediction of shelf-life of foods such as fresh meat, poultry and fish as well as dairy products such as milk, cheese and yoghurt. Also affected are brad, cured meat, fruit juices and fruits and vegetables. The basic methods for the control of micro-organisms are the following: - Lower temperature to slow growth Raise temperature to kill them Remove or bind water to slow or prevent growth Lower pH Control O2 or CO2 level to control population Manipulate food composition to remove nutrients needed by the microbes Add preservatives (e.g. sodium benzoate)
  45. 45. MAP, CAP and Active Packaging
  46. 46. Active packaging Active packaging does more than simply provide a barrier to outside influences. It can control, and even react to, events taking place inside the package. Fresh foods just after harvest or slaughter are still active biological systems. The atmosphere inside a package constantly changes as gases and moisture is produced during metabolic processes. The type of packaging used will also influence the atmosphere around the food because some plastics have poor barrier properties to gases and moisture. The metabolism of fresh food continues to use up oxygen in the headspace of a package and increases the carbon dioxide concentration. At the same time water is produced and the humidity in the headspace of the package builds up. This encourages the growth of spoilage micro-organisms and damages the fruit and vegetable tissue. Many food plants produce ethylene as part of their normal metabolic cycle. This simple organic compound triggers ripening and ageing. This explains why fruit such as bananas and avocados ripen quickly when kept in the presence of ripe or damaged fruits in a container and broccoli turns yellow even when kept in the refrigerator.
  47. 47. Ethylene scavenging A chemical reagent, incorporated into the packaging film, traps the ethylene produced by ripening fruit or vegetables. The reaction is irreversible and only small quantities of the scavenger are required to remove ethylene at the concentrations at which it is produced. Systems developed are already commercially available. These usually involve the inclusion in the package of a small sachet, which contains an appropriate scavenger. The sachet material itself is highly permeable to ethylene and diffusion through the sachet is not a serious limitation. The reacting chemical for ethylene is usually potassium permanganate, which oxidises and inactivates it. However many other possibilities are conceivable: activated charcoal impregnated with an oxidising agent such as KBRO3; electron deficient aromatic compounds (e.g. dicarboxyoctyl ester substituted benzene); or simply ethylene absorbing compounds such as activated charcoal, molecular sieves or clay materials.
  48. 48. Carbon dioxide release High carbon dioxide levels are desirable in some food packages because they inhibit surface growth of micro-organisms. Fresh meat, poultry, fish, cheeses and strawberries are foods, which can benefit from packaging in a high carbon dioxide atmosphere. However with the introduction of modified atmosphere packaging there is a need to generate varying concentrations of carbon dioxide to suit specific food requirements. Since carbon dioxide is more permeable through plastic films than is oxygen, carbon dioxide will need to be actively produced in some applications to maintain the desired atmosphere in the package. So far the problems associated with diffusion of gases, especially carbon dioxide, through the package, have not been resolved and this remains an important research topic.
  49. 49. Other developments Other systems of active packaging which are either already available or could soon be seen in the market place include: - sachets containing iron powder and calcium hydroxide which scavenge both oxygen and carbon dioxide. These sachets are used to extend the shelf life of ground coffee. - film containing microbial inhibitors other than those noted above. Other inhibitors being investigated include metal ions and salts of propionic acid. - specially fabricated films to absorb flavours and odours or, conversely, to release them into the package.
  50. 50. Innovations and Trends Looking ahead Innovation is an essential Factor ? Product Material Machine Packaging Trends: - Differentiation - Existing function - New Technologies ....types of packaging - User Obser- to create new ap- - Fast speed and serving size vation plication - Greater flexibility trends. - Socioeconomic - Reduce cost-in- - Mass customi- use sation - Health and Safety Market Trends and Drivers: Competitive Trends: - Kids and Teenagers - Competing on Convenience - Ready-to-use Products on Hand - Importance of being smaller - Cooking Trends - Meals and Side Dishes - Parameters for Convenience - Dairy Products - Expanding Distribution - Beverages - Package Sizes - Snacks and Confectioneries - Vending Machine Trends - Health & Personal Care - Natural Food Store Trends - etc. - Warehouse Club Trends - Convenience Store Trends