Protective atmosphere

A protective atmosphere or protective gas atmosphere is used in the storage and packaging of food in order to slow down the aging process and thus extend the shelf life. The protective atmosphere consists of various protective gases that are contained in the air . But it has a mixture that differs from the air; H. relative composition. Protective gases are therefore naturally occurring components of the air, the proportions of which in the protective atmosphere must be adapted depending on the area of application. According to Section 9 of the Additive Admissions Ordinance , it is not necessary to specify the type of protective gases in the protective atmosphere. However, the note “packed in a protective atmosphere” must be given.

Areas of application

Protective atmosphere is used in agriculture under the name Controlled Atmosphere (CA) for storage . With a significantly reduced oxygen content, low temperatures, increased humidity and enrichment with carbon dioxide , the natural ripening process of fruit , vegetables and flowers is slowed down and the shelf life is extended. The process is also used for long shipments ( e.g. banana transport ). Controlled atmosphere means that the storage conditions are constantly monitored and readjusted.

In the Modified Atmosphere Packaging (MAP) area, the protective atmosphere is given as packaging gas together with the product in the mostly gas-tight packaging. By packaging in a suitable protective atmosphere, it is possible to extend the shelf life with high quality - depending on the product - by days or weeks. This simplifies sales logistics and warehousing , as goods have to be delivered less often and over greater distances. At the same time, there is less spoilage and returns if hygiene conditions and the cold chain are always monitored and adhered to. Unlike many other types of preservation ( tin , freezing , heating (z. B. pasteurization ), curing , radiation , drying , loading , fermentation and adding preservatives ) the product itself remains unchanged, without affecting the quality or taste. Due to the packaging in a protective atmosphere, it is z. For example, it is only possible to offer peeled or kitchen-ready vegetables and salads or industrially produced fresh meat for sale in supermarkets.

history

The French natural scientist and chemist Jacques Étienne Bérard carried out the first scientific studies with protective atmospheres in 1821. He studied the effects of various gases on the ripening of fruits. Bérard realized that harvested fruits consume oxygen (O ₂ ) and give off carbon dioxide (CO ₂ ) and that ripening is slowed down by reducing oxygen. However, these findings were not used commercially.

The French chemist and microbiologist Louis Pasteur and his assistant Joubert found out in 1877 using the example of Bacillus anthracis that carbon dioxide inhibits the growth of bacteria or kills them. Five years later, the German Hermann Kolbe published that the anhydride of carbon dioxide (CO ₂ ) considerably extends the shelf life of ox meat. After 14 days the meat was colored gray on the outside, but it was “tasty and indistinguishable from fresh meat”. After three weeks of storage, the taste of the meat was still of the same quality, but the meat had "become softer and required a shorter time to cook".

In the following, numerous publications were made about the inhibiting effect of CO ₂ on microorganisms. In 1933, for example, Haines found that at low temperatures around zero ° C, concentrations of 10–20% carbon dioxide were sufficient to significantly reduce the growth of bacteria on meat. Under these conditions, compared to storage in air at the same temperature, the time until the number of bacteria doubled was reduced by half.

The first significant application of the protective atmosphere was in the early 1930s when storing apples in an atmosphere with reduced oxygen content and increased carbon dioxide content, as well as when transporting fruit in the storage rooms of ships. It was found that even cattle carcasses in a modified atmosphere achieved a shelf life of 100% longer when transported over long distances.

The packaging of fresh meat in a controlled atmosphere (MAP) was already carried out in the USA in the mid-1970s. This extended the shelf life, which resulted in new sales channels. Supermarkets in particular offered more and more goods packaged under protective gas.In Germany, the discounter Penny and Plus began selling packaged fresh meat in the early 2000s. The breakthrough came in 2003/2004, when Aldi and Lidl expanded their range accordingly.

Types of shielding gases, mode of action and labeling

The most important protective gases are carbon dioxide, nitrogen and oxygen. Other gases are also used, the properties of which are described below.

nitrogen

Protective atmosphere without oxygen

Nitrogen (N ₂ ) is about 78% in air. It is an inert gas and therefore does not react directly with the food. It is used as a packing gas in particular to displace oxygen from the air. This indirectly prevents the oxidation of food and inhibits the growth of oxygen-dependent ( aerobic ) microorganisms . It is also often used as a filling gas because it diffuses very slowly through packaging films and therefore remains in the pack for a long time. It is approved as a food additive under the E number E 941 as a packaging gas for all foods and may also be used for the packaging of organic products. There is no limit to the maximum amount. Nitrogen has no harmful effects on health and is also odorless and tasteless.

carbon dioxide

Carbon dioxide or carbon dioxide for short is a chemical combination of carbon and oxygen with the chemical formula CO ₂ . The colorless gas dissolves well in water and has slightly acidic properties. It is contained in normal air at around 0.04%.

As a packing gas, it is used in addition to nitrogen to displace oxygen and thus inhibits undesired oxidation processes that are often associated with the loss of structure, color and aroma. At concentrations greater than 20%, it also effectively inhibits the growth of oxygen-dependent (aerobic) bacteria and mold . It dissolves in liquid and fat phases and thus forms an acidic environment on the surface of the product, which makes it difficult for bacteria to settle. Carbon dioxide is often used to increase shelf life, the shelf life usually increasing with its concentration. However, if the dosage is too high, some foods can become acidic more quickly. In addition, when it penetrates biological membranes, it changes their permeability and function. However, the gas can more easily diffuse through the packaging. This, as well as the reaction with the product, can cause the packaging to collapse over time. Carbon dioxide is declared as a packing gas under the E number E 290.

oxygen

Food packaging with intact packaging (top) and product storage with faulty sealing seam (bottom). Air has flowed into the packaging through the leaky sealing seam so that the breakfast bacon no longer looks so red.

Oxygen (O ₂ ) occurs in normal air with a concentration of about 21% and forms the prerequisite for the growth of aerobic microorganisms. The gas is more likely to promote oxidation-related spoilage of the food. Therefore, the oxygen within the protective atmosphere is normally significantly reduced or even excluded. When packaging red fresh meat, the proportion of oxygen is significantly increased in order to maintain or even intensify the red color of the meat. In addition, high oxygen concentrations inhibit the growth of anaerobic microorganisms. Fruit and vegetables also need certain amounts of oxygen (3 to 10%) for cell respiration after the harvest, which must also be taken into account when storing and packaging. Oxygen is an additive with the European approval number E 948.

argon

Argon (Ar) is a noble gas with a proportion of 0.9% in the air. Like nitrogen, it has inert properties so that it does not react with the food. It is heavier than air, so when it is introduced into a vessel it displaces the residual oxygen more efficiently than when purging with nitrogen. However, argon is significantly more expensive compared to nitrogen. Argon is part of recent studies. Taste tests with potato chips showed a 25% longer shelf life. Argon is sometimes used in the packaging of wine. It is believed that certain enzyme activities are inhibited and argon slows down metabolic reactions in some vegetables. Argon is listed as an additive for food under the E number E 938 with the function as a packing gas. Argon can also be used for the packaging of organic food.

helium

As a noble gas, helium (He) is also inert. Although it is approved as a packaging gas for food under the E number E 939, it is only used to a limited extent because its small molecule size means that it diffuses very easily through packaging and is also very expensive. It is sometimes used as an auxiliary gas to localize leaks.

hydrogen

Hydrogen (H ₂ ) is approved as an additive for food under the E number E 949 as a packing gas. However, it may not be used for packaging organic products. Due to its small molecule size, it escapes from the packaging very quickly. It is sometimes used as a test gas to check for leaks.

Carbon monoxide

Carbon monoxide (CO), or carbon monoxide for short, is a poisonous gas that is only found in traces in the air. Nevertheless, it can be used in concentrations of up to 0.4% for packaging red meat or red fish. This has been done in Norway since 1970, and has also been used in the USA since 2004 . In the European Union , carbon monoxide is banned as a food additive and therefore does not have an E number.

Carbon monoxide gives red meat a cherry-red color without using high amounts of oxygen in the packaging. Meat treated with oxygen shows a light red color due to the formation of oxymyoglobin , while the slightly darker carboxymyoglobin is formed when carbon monoxide is added.

Application examples and typical gas compositions

In most applications, other gases displace the oxygen from the packaging as much as possible to extend the shelf life. At the same time, carbon dioxide is used in a proportion greater than 20% in order to additionally inhibit bacterial growth, with attempts being made to use the highest possible proportions of it. Nitrogen is usually used as the supporting gas.

Cheese with appropriate packaging

Depending on the food, very high concentrations of carbon dioxide can cause undesired changes to the product or the packaging. Cream becomes slightly acidic, so foods containing cream are preferably packaged in nitrogen or a gas mixture with rather low carbon dioxide concentrations. Hard cheese tolerates very high levels of carbon dioxide, which effectively prevents the formation of mold, but does not hinder the cheese's ripening process . In soft cheese with a high moisture content, however, carbon dioxide dissolves, so there is a risk that the gas-tight packaging will collapse. A similar problem arises when the surface area (e.g. grated cheese) is very high. With concentrations of 50% and more, nitrogen as a supporting gas prevents the packaging from collapsing.

Fish and seafood are among the most sensitive foods. Immediately after the catch there is a risk of rapid loss of quality and spoilage. This is due to microorganisms and enzymes that thrive at neutral pH values. In addition, the fat becomes rancid particularly quickly when it comes into contact with oxygen. For raw fish, temperature control of close to 0 ° C (without interrupting the cold chain), as well as a precisely adapted protective atmosphere, with carbon dioxide shifting the pH value into the acidic range, is particularly important. However, excessively high concentrations of carbon dioxide can lead to undesirable side effects such as loss of fluid or a sour taste. With some shellfish, on the other hand, about 30% oxygen is deliberately added to maintain the color.

In the case of snacks, potato chips , nuts , spices and coffee , the greatest danger is the high fat content. Oxidation quickly turns fats rancid . In these cases, excluding oxygen is sufficient, so that mostly a pure nitrogen atmosphere is used in the packaging. The nitrogen also provides cushioning for shock-sensitive potato chips in tube packaging.

Baked goods in protective packaging

In the case of bread and baked goods , the growth of mold must be prevented, while the growth of other microorganisms is rarely a problem due to the low water activity. Molds can be easily controlled with large amounts of carbon dioxide and a low percentage of oxygen. Tests on toast infected with mold showed that the time until molds develop in an atmosphere of 99% nitrogen and 1% oxygen is 5 days, while in an atmosphere of 99% carbon dioxide and 1% oxygen it takes 100 days to become one Mold growth came. However, the type of atmosphere has little or no influence on staling (regression of starch). Storage at low temperatures, on the other hand, accelerates staling, so that baked goods that are eaten cold are stored at room temperature. In the case of baked goods that are warmed up before they are served (baked rolls), the stale baking process is reversed, so that lower storage temperatures can also be used here.

Meat and meat products

Natural discoloration of beef begins when exposed to air

Raw meat is particularly susceptible to bacterial attack due to its high moisture and nutrient content. The problem is exacerbated especially with minced meat, which has a very large surface in comparison. If you try to curb the growth of bacteria by removing oxygen from the atmosphere, red meat and especially beef turn gray and the impression of freshness is lost. In order to suppress these color changes in red meat and to maintain or even intensify the red color, the packaging gas contains very high proportions of oxygen of 60–80% (remainder CO ₂ ), whereby the muscle pigment myoglobin reacts with the oxygen. The increase in shelf life, on the other hand, is solely due to the carbon dioxide (20–40%), which dissolves in the surface of the meat and thus lowers the pH value . The acidic environment reduces the growth of bacteria. The typical shelf life increases at a constant temperature of 2–3 ° C from 2–4 days in air to around 5–8 days in the modified atmosphere.

Light poultry, on the other hand, do not need any protection against discoloration. Therefore, no oxygen is contained in the corresponding protective gas. Rather, packing gases with typically 40–100% carbon dioxide are used (the remainder nitrogen as an inert support gas). At a constant temperature of 2–3 ° C and in a hygienically perfect condition, a shelf life of up to 21 days can be achieved under a protective gas atmosphere (gas volume of 100–200 ml of gas per 100 g of meat). If the storage temperature is only slightly higher than 4–6 ° C, the shelf life is reduced to only about 12 days.

fruit and vegetables

Fresh fruit and vegetables place special demands on packaging and atmosphere. Unlike other foods, fresh fruits and vegetables continue to breathe after they are harvested. To do this, they need an oxygen content of 3–10% inside the packaging. In addition, the packaging must have a certain permeability (permeability) for gases. Otherwise, breathing would lead to anaerobic states (<1% O ₂ and> 20% CO ₂ ), which would result in significant quality losses. The permeability tailored to the product can, for. B. can be generated by a film with micro-perforation. One speaks of a balanced protective atmosphere (Equilibrium Modified Atmosphere = EMA).

packaging

Test of the composition of the atmosphere in packaged carrots

The packaging plays an important role in protective gas packaging. Composite films made up of several layers are used. The most important properties of the packaging are gas tightness, sealability, transparency, mechanical protection and stackability. A gas and leakage analysis integrated in the packaging machine helps to ensure the necessary quality.

criticism

In 2010, the use of a modified atmosphere in the packaging of meat came under criticism because large food chains use an increased oxygen concentration under the same title. The purpose is a chemical reaction on the surface that makes the meat appear red and rosy even after it has spoiled, as well as preventing the growth of Clostridium botulinum under anaerobic conditions. However, the opposite effect occurs in comparison to a low-oxygen protective atmosphere and the meat spoils more quickly and fat becomes rancid. According to information from the BfR, oxidation of the cholesterol can lead to changes and impairment of the taste of the meat under such protective atmospheres, but these are not harmful to health.

In the case of perishable minced meat, in particular, compliance with the cold chain is absolutely essential in order to suppress the multiplication of germs. Normally, temperatures of a maximum of +2 ° C are required here, which can hardly be reached in a household refrigerator. To protect the industry, there is also a warning on the packaging that the mince must be completely heated before consumption and is not suitable for raw consumption. However, if you rely on the consistency and color of roasting, you can be deceived because, in contrast to untreated meat, meat packed with inert gas changes its color and firmness at 50 ° C, while most germs are only killed at 70 ° C.

Individual evidence

^ ^A ^b Gordon L. Robertson: Food Packaging: Principles and Practice, Third Edition . 3. Edition. CRC Press, 2016, ISBN 978-1-4398-6242-1 , History of MAP, pp. 430-431 (English, google.de [accessed June 10, 2018]).
^ Antiseptic properties of carbonic acid. In: Polytechnisches Journal . 247, 1883, Miszelle 4, p. 226.
↑ Haines, RB: The influence of carbon dioxide on the rate of multiplication of certain bacteria, as judged by viable counts. In: Journal of the Society of Chemical Industry . tape 52 . London 1933, p. 13T-17T .
↑ ^a ^b ^c meat market under the oxygen tent. (PDF) How the food retail trade systematically leads consumers to believe that packaged meat is “freshness” and thus expects them to lose quality and pose health risks. foodwatch eV, August 2010, accessed on May 13, 2018 .
↑ Frank Massholder: Nitrogen: Packing gases: Definition, product knowledge, food science: Lebensmittellexikon.de. Retrieved April 22, 2018 .
↑ ^a ^b ^c ^d ^e ^f ^g ^h The ultimate combination for freshness. MAPAX® naturally extends shelf life. (PDF) Linde AG, accessed on April 27, 2018 .
↑ Frank Massholder: Carbon dioxide: Packing gases: definition, goods science, food science: food lexikon.de. Retrieved April 23, 2018 .
↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j Packing in a protective atmosphere. Typical gases for packaging under modified atmosphere packaging. WITT-GASETECHNIK GmbH & Co KG, accessed on April 23, 2018 .
↑ Food packed in argon will last longer - Wissenschaft.de . In: Wissenschaft.de . August 28, 2001 ( Wissenschaft.de [accessed April 27, 2018]).
↑ Packing gases . ( Spektrum.de [accessed on June 16, 2018]).
↑ Frank Massholder: Argon: Packing gases: Definition, goods science, food science: food lexikon.de. Retrieved April 24, 2018 .
↑ Packing gases keep food without preservatives . In: EAT SMARTER . ( eatsmarter.de [accessed April 24, 2018]).
↑ Food hygiene and food law aspects of the use of carbon monoxide as a component in the packaging of meat and fish products. In: 45th working conference AK food hygiene Garmisch-Patenkirchen. 2004, accessed September 21, 2018 .
^ "Whitewashing" of fish with carbon monoxide | Nds. State Office for Consumer Protection and Food Safety. Retrieved on September 22, 2018 (German).
^ Report from foodwatch , accessed on September 13, 2015.
^ Report on Swiss television broadcast Kassensturz in January 2011.
↑ Publication 12/2010 by the Federal Institute for Risk Assessment August 5, 2010.
↑ Packaged minced meat: Fresh for a week? swr Marktcheck, January 19, 2016, accessed on July 18, 2018 .

[:2-1] A ^b Gordon L. Robertson: Food Packaging: Principles and Practice, Third Edition . 3. Edition. CRC Press, 2016, ISBN 978-1-4398-6242-1 , History of MAP, pp. 430-431 (English, google.de [accessed June 10, 2018]).

[2] Antiseptic properties of carbonic acid. In: Polytechnisches Journal . 247, 1883, Miszelle 4, p. 226.

[3] Haines, RB: The influence of carbon dioxide on the rate of multiplication of certain bacteria, as judged by viable counts. In: Journal of the Society of Chemical Industry . tape 52 . London 1933, p. 13T-17T .

[:3-4] meat market under the oxygen tent. (PDF) How the food retail trade systematically leads consumers to believe that packaged meat is “freshness” and thus expects them to lose quality and pose health risks. foodwatch eV, August 2010, accessed on May 13, 2018 .

[5] Frank Massholder: Nitrogen: Packing gases: Definition, product knowledge, food science: Lebensmittellexikon.de. Retrieved April 22, 2018 .

[:1-6] ↑ ^a ^b ^c ^d ^e ^f ^g ^h The ultimate combination for freshness. MAPAX® naturally extends shelf life. (PDF) Linde AG, accessed on April 27, 2018 .

[7] Frank Massholder: Carbon dioxide: Packing gases: definition, goods science, food science: food lexikon.de. Retrieved April 23, 2018 .

[:0-8] ↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j Packing in a protective atmosphere. Typical gases for packaging under modified atmosphere packaging. WITT-GASETECHNIK GmbH & Co KG, accessed on April 23, 2018 .

[9] Food packed in argon will last longer - Wissenschaft.de . In: Wissenschaft.de . August 28, 2001 ( Wissenschaft.de [accessed April 27, 2018]).

[10] Packing gases . ( Spektrum.de [accessed on June 16, 2018]).

[11] Frank Massholder: Argon: Packing gases: Definition, goods science, food science: food lexikon.de. Retrieved April 24, 2018 .

[12] Packing gases keep food without preservatives . In: EAT SMARTER . ( eatsmarter.de [accessed April 24, 2018]).

[13] Food hygiene and food law aspects of the use of carbon monoxide as a component in the packaging of meat and fish products. In: 45th working conference AK food hygiene Garmisch-Patenkirchen. 2004, accessed September 21, 2018 .

[14] "Whitewashing" of fish with carbon monoxide | Nds. State Office for Consumer Protection and Food Safety. Retrieved on September 22, 2018 (German).

[foodwatch-15] Report from foodwatch , accessed on September 13, 2015.

[Kassensturz-16] Report on Swiss television broadcast Kassensturz in January 2011.

[copt-17] Publication 12/2010 by the Federal Institute for Risk Assessment August 5, 2010.

[18] Packaged minced meat: Fresh for a week? swr Marktcheck, January 19, 2016, accessed on July 18, 2018 .