Gas flush consists of an inert gas such as nitrogen, carbon dioxide, or exotic gases such as argon or helium which is injected and frequently removed multiple times to eliminate oxygen from the package. This technique is called MAP (Modified Atmosphere Packaging). Most common applications for MAP include coffee, snack foods, pre-baked products, meat and poultry, as well as other more sophisticated applications.
Why Use Gas Flush
When modifying the atmosphere inside of a package, the amount of oxygen can typically be reduced to 3% or less. Inert gases used for MAP are typically denser than oxygen. As such, the oxygen inside the package is forced out of the package. This results in extended product shelf life, product integrity, protection against discoloration, and for products like chips, a cushion-like buffer against damage (this is commonly referred to as a “pillow pack”).
Many gas flush applications require sophisticated gas mixtures. Case ready meat applications are a good example of a sophisticated gas mixture which requires a nitrogen, carbon dioxide and carbon monoxide mixture (Tri-Gas). Nitrogen is an inert gas that functions to fill the headspace in the package. Carbon dioxide is added for its antimicrobial properties and carbon monoxide stabilizes the typical red or pink color of air-exposed meat.
Some companies have used dry nitrogen to reduce the size of a desiccant packet in high volume semi-conductor packaging applications spread over 300,000 - 400,000 packages. The cost reduction for the total package or sorbent system easily results in savings that could provide the capital for the vacuum sealing equipment.
Common MAP Gases
Carbon dioxide (CO2)
Carbon dioxide inhibits the growth of most aerobic bacteria and molds. Generally speaking, the higher the level of CO2 in the package, the longer the achievable shelf-life. However, CO2 is readily absorbed by fats and water - therefore, most foods will absorb CO2. Excess levels of CO2 in MAP can cause flavor tainting, drip loss and pack collapse. It is important, therefore, that a balance is struck between the commercially desirable shelf-life of a product and the degree to which any negative effects can be tolerated. When CO2 is required to control bacterial and mold growth, a minimum of 20% is recommended.
Nitrogen is an inert gas and is used to exclude air and, in particular, oxygen. It is also used as a balance gas (filler gas) to make up the difference in a gas mixture, to prevent the collapse of packs containing high-moisture and fat-containing foods, caused by the tendency of these foods to absorb carbon dioxide from the atmosphere. For modified atmosphere packaging of dried snack products 100% nitrogen is used to prevent oxidative rancidity. Oxygen (O2)
Oxygen causes oxidative deterioration of foods and is required for the growth of aerobic micro-organisms.
Generally, oxygen should be excluded but there are often good reasons for it to be present in controlled quantities including:
Maintain fresh, natural color (in red meats for example)
To maintain respiration (in fruit and vegetables)
To inhibit the growth of aerobic organisms (in some types of fish and in vegetables)
Argon has the same properties as nitrogen. It is a chemically inert, tasteless, odorless gas that is heavier than nitrogen and does not affect micro-organisms to any greater degree. It is claimed to inhibit enzymic activities, microbial growth and degradative chemical reactions (CCFRA R&D Report 125). Hence it can be used in a controlled atmosphere to replace nitrogen in most applications. Its solubility (twice that of nitrogen) and certain molecular characteristics give it special properties for use with vegetables. Under certain conditions, it slows down metabolic reactions and reduces respiration.
Carbon monoxide is a toxic, colorless, odorless, flammable gas. It is stable at up to 400°C with respect to decomposition into carbon and oxygen.
Results have shown that the use of carbon monoxide (CO) in MAP with high levels of CO2 has resulted in increased shelf-life together with retention of the bright red color of meat cuts. It is also claimed that carbon monoxide can effectively reduce or inhibit different spoilage and pathogenic bacteria.
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