Modified Atmosphere Packaging

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Food packaging with intact packaging (above) and with a faulty sealing seam (below) through which air has flowed into the packaging, which has led to the discoloration of the bacon.

Modified Atmosphere Packaging ( English "packaging with modified atmosphere", abbreviated to MAP ), packaging in a protective atmosphere or protective gas packaging means the targeted change in the gas composition of a mostly gas-tight packaging during the closing process. A major cause of food spoilage in unopened packaging is the oxygen that remains in the packaging during the packaging process. By introducing inert or inert gases , the protective gases , during packaging, the oxygen is displaced to a large extent from the packaging, which can increase the shelf life of the food in the unopened packaging many times over. An alternative to modified atmosphere packaging is vacuum packaging , which also reduces the amount of oxygen in the vicinity of the product.

Packing gases

Depending on the type of packaged goods , nitrogen and carbon dioxide are often used as packing gases . The composition of the packaging gas (mixing ratio of the gases) must be adapted to the product to be packaged and its specific sensitivity. In addition, a combination with cool storage is usually recommended. During packaging, the gases are either freshly mixed from pure, “food-grade gases” or delivered as pre-prepared gas mixtures.

Packaging materials

A good initial quality of the product and raw materials, a suitable and controlled temperature and good hygiene conditions (e.g. HACCP ) are prerequisites for protective gas packaging . Packaging takes on a very important task in modified atmosphere packaging. Depending on the product, composite films are made up of several layers that have different properties:

  • Gas tightness: So that neither the protective atmosphere escapes nor oxygen penetrates the packaging, the film and the weld seams must have a high barrier function for gases. This is achieved by layers such. B. made of polyester (PET), polyamide (PA), ethylene vinyl alcohol (EVOH), acrylonitrile (PAN), polyvinylidene chloride (PVdC), polyvinyl chloride (PVC) or aluminum (Al) possible. Exceptions to the gas tightness apply to the packaging of fresh fruit and vegetables , as these products continue to breathe after the harvest, which would steadily reduce the concentration of oxygen in the packaging. The film for fruit and vegetables must have a permeability (micro-perforation) tailored to the product quantity so that the oxygen concentration in the packaging remains between 3 and 10%. One then speaks of a balanced protective atmosphere (Equilibrium Modified Atmosphere = EMA).
  • Sealability: Other layers of the composite film are decisive for ensuring that the composite film can be welded or glued and that permanent tightness along the sealed seam is guaranteed. For this purpose, the layer of the composite film facing the product is usually made of polyethylene (LDPE or HDPE). Some packaging (e.g. for cheese or sausage slices) also includes the function of being resealable.
  • Transparency and anti-fog properties: completely transparent foils are used so that the customer can see the product directly. Anti-fog properties on the inside of the material prevent the formation of water droplets, which would reduce the transparency. This is particularly necessary when the packaged product gives off moisture. Some products, on the other hand, have to be protected from light or should not be directly visible from the outside. Intermediate layers made of aluminum are suitable for this.
  • Moisture Barrier: Loss of moisture leads to weight loss and dehydration of the food. In order to reduce the water vapor permeability of the packaging, there is typically a layer of polyethylene (HDPE), polypropylene (PP) or polyvinylidene chloride (PVdC) in the composite film .
  • Mechanical protection and stackability: Packaging also offers mechanical protection and ensures the necessary stability during transport and sale. Both thinner foils as covers or thicker foils as thermoformed or foamed shells are used. Trays also allow the product to be stacked. When packaging potato chips , the film of the tubular packaging, together with the enclosed protective gas, provides cushioning so that the sensitive contents do not break. On the one hand, the film should be stable, but on the other hand it should also allow the packaging to be opened without tools (knife or scissors).
  • Microwave suitability: For finished products it is becoming increasingly important that the packaging is suitable for heating the food in the microwave oven . The packaging can be used for serving or as a plate at the same time. In some packaging, a pressure relief valve allows the water vapor that is generated when the product is heated to escape.
  • Price and recyclability: In addition to optimal protection of the product, other aspects such as attractiveness and price are also important. Recyclability is also becoming increasingly important.

Active and intelligent packaging

A more recent development is active packaging that can absorb or release substances. Oxygen absorption on the inside of the packaging can further reduce the residual oxygen and thereby increase the shelf life. The targeted absorption or release of the ripening gas ethene can control the ripening process of the product. The antimicrobial effect of the packaging can inhibit the growth of germs. In addition to these properties, some of which are useful, there are also approaches to aroma regulation, whereby foreign aromas are suppressed. Here, however, there is a risk that odorous substances are also bound, which are intended to warn the consumer about the spoilage of the food. The components of active packaging are not subject to labeling, so that it is not clear to the consumer which of these technologies are used.

In the case of strongly degassed products such as roasted coffee beans , fresh sauerkraut or fresh dough products , packaging is equipped with a one-way pressure relief valve ( aroma protection valve ). It allows gases to escape from the pack and therefore prevents the pack from inflating. The opening pressure of the valve is typically in the range of a few millibars . At the same time, the valve prevents oxygen from penetrating, which could reduce the taste or shelf life.

Intelligent packaging shows the condition of the goods. Freshness indicators show the retailer or customer changes in the chemical composition of the gas inside the packaging via a color change. In this way, leaks in the packaging can be signaled via oxygen indicators. Other indicators show the formation of chemical compounds such as sulfur dioxide , which are formed when food is spoiled. Such indicators are already in use in some countries such as the USA, Sweden or France . Other systems detect components of fruit aromas and thus provide information on the degree of ripeness of fruit. Some of them are found in the USA and New Zealand .

Other intelligent packaging uses time-temperature indicators (TTI) to show whether the cold chain has been broken. These indirect systems measure the heat dose absorbed over time, which is often responsible for premature spoilage. However, since the indicator only registers the amount of heat and not the time when the temperature is exceeded, the effects on the food can be different. Exposure to light or moisture can also accelerate the loss of freshness - factors that are not captured by the indicators. In the US, TTI labels are mandatory for seafood packaging .

Packaging machines

Overall, there are different main groups of packaging machines that are used for MAP technology. However, the basic principle is similar everywhere. First a container is formed or a finished container is used, which is then filled with the product. The ambient air is then replaced by the protective atmosphere. The gas exchange takes place either by gas purging or by vacuum extraction with subsequent back gassing with the protective gas. Purging with protective gas is a continuous process, whereby relatively high packaging speeds can be achieved. The vacuum extraction takes longer, but the gas exchange is more efficient with regard to the residual oxygen content. Finally, the packaging is sealed.

Vertical flow wrapping machine

The vertical tubular bag machine (also called vertical bagging machine) is used to fill pourable or liquid products such as B. coffee beans, peanuts, potato chips, mustard or ketchup. The flat film is unrolled from a roll and formed into a tube via a forming shoulder. The tube is closed lengthways by the longitudinal sealing device and at the bottom by the transverse sealing device. After weighing, the product falls through a filling pipe into the hose, which is open at the top, while the protective gas is fed in at the same time. After filling, the tube is closed at the head with a double seal seam. The hose is then cut through between the two sealing seams so that a new hose that is already closed at the bottom remains in the machine. The transverse sealing device is moved along with the hose to increase the speed.

Horizontal flow wrapping machine

The horizontal tubular bag machine (also known as the horizontal bagging system) is suitable for packing piece goods such as bread, baked goods, piece of cheese or green salads. The packaged goods are placed on the horizontally arranged film, the tube is formed around the packaged goods and welded either above or below the product in the running direction of the film. A flat gas supply tube extends in the hose to just before the transverse sealing zone so that the protective atmosphere is flushed out of the hose in countercurrent to the incoming packaged goods. In this way, residual oxygen levels of 0.5 to 1% can be achieved. Only in the case of very porous goods does the air in the pores have to be exchanged before packaging, for example by pre-evacuation and gas flushing. In the area of ​​the cross sealing zone, the tube is sealed at both ends and cut into individual bags. As with the vertical form, fill and seal machine, only one roll of film is sufficient for the packaging.

Thermoforming machine

Two different types of film are used in this packaging machine. The lower film is made much more stable and is formed into a shell by using heat in a forming station. The product is placed in this bowl and then everything is evacuated together. The protective gas is introduced and the filled packaging is sealed by welding on an upper film. Typical areas of application are the packaging of meat, fish, cold cuts or ready meals.

Tray sealing machines

Tray sealing machines work in a similar way to thermoforming machines, except that the forming station for thermoforming the trays is omitted. The trays are usually much more stable and are placed directly in the machine. Typical areas of application are the packaging of meat salad or coleslaw. A lid is often put over the top film.

Gas and leakage analysis

Test of the composition of the atmosphere in packaged carrots

In addition to very good hygienic conditions, modified atmosphere packaging places high demands on the gas composition and the tightness of the packaging. Most packaging machines therefore contain detectors for inline gas analysis, which continuously monitor the gas composition during packaging. In order to improve the measurement accuracy, gas measurements are also carried out randomly in the laboratory for quality control , with the gas being taken from the packaging via a needle.

Leaks are caused by defects in the film or the sealed seam. Pores with a size of one micrometer are sufficient for gas exchange . One of the most common problems is that of product inclusions in the sealing seam that prevent the packaging from welding. The leakage analysis takes place in a chamber with negative pressure. Gas sensors can detect even small amounts of the escaping test gas and thus also the smallest leaks quickly and reliably. The carbon dioxide already contained in the packaging is usually used as the test gas. The leak test is carried out non-destructively within a few seconds and is therefore often integrated into the packaging process as a 100% check. However, this method does not allow localization of the leak.

Another method of leak testing is a water bath. The pack is placed in a chamber filled with water and submerged. Gas bubbles escape from leaks and mark the leak. If necessary, the effect can be enhanced by applying a vacuum to the chamber. This method requires experience on the part of the examiner and is not as sensitive to micro-leaks. The product can no longer be put on sale after testing.

Individual evidence

  1. ^ A. Keith Thompson: Fruit and Vegetables Harvesting, Handling and Storage, 2003, Blackwell Publishing, Oxford, ISBN 1-4051-0619-0 , pp. 61-70
  2. ↑ a b c d e f g The ultimate combination for freshness. MAPAX® naturally extends shelf life. (PDF) Linde AG, accessed on June 3, 2018 .
  3. ↑ a b Packing in a protective atmosphere. Typical gases for packaging under modified atmosphere packaging. WITT-GASETECHNIK GmbH & Co KG, accessed on April 23, 2018 .
  4. ↑ Active packaging. Consumer Center NRW eV, March 29, 2018, accessed on June 11, 2018 .
  5. ↑ Stefanie Krauß: It's a matter of taste: valve technology for the best product protection . In: Bosch Packaging Technology . November 12, 2012 ( boschpackaging.com [accessed September 14, 2018]).
  6. ↑ Inert gas packaging for coffee. Wipf AG, accessed on September 14, 2018 .
  7. ↑ a b Dr Johannes Bergmair, Dr Michael Washüttl, Dr Beatrix Wepner: Testing practice for plastic packaging: food, pharmaceutical and cosmetic packaging . Behr's Verlag DE, 2012, ISBN 978-3-89947-941-6 , 6.4.2 Intelligent packaging ( google.de [accessed on June 16, 2018]).
  8. ↑ a b c Intelligent packaging. Consumer Center NRW eV, March 29, 2018, accessed on June 11, 2018 .
  9. ↑ Monika Kaßmann: Fundamentals of packaging: guidelines for interdisciplinary packaging training . Beuth Verlag, 2014, ISBN 978-3-410-24193-5 , pp. 230 ( google.de [accessed June 5, 2018]).
  10. ↑ Animation of an automatic vertical packaging machine (VFFS). ULMA Packaging GmbH, accessed on May 10, 2018 .
  11. ↑ Norbert S. Buchner: Packaging of foods: Food technology, packaging technology and microbiological basics . Springer-Verlag, 2013, ISBN 978-3-642-58585-2 , pp. 240 ( google.de [accessed on June 5, 2018]).
  12. ↑ Animation of an automatic horizontal flow wrapping machine (HFFS). ULMA Packaging GmbH, accessed on May 10, 2018 .
  13. ↑ Animation of a thermoforming line. ULMA Packaging GmbH, accessed on May 10, 2018 .
  14. ↑ Animation of a tray sealing system. ULMA Packaging GmbH, accessed on May 10, 2018 .
  15. ↑ a b Know how! The right leak test for every packaging. WITT-GASETECHNIK GmbH & Co KG, accessed on June 16, 2018 (German).