Modified atmosphere
Oxygen also helps maintain high respiration rates of fresh produce, which contribute to shortened shelf life.
Oxygen scavengers may also be used to reduce browning due to lipid oxidation by halting the auto-oxidative chemical process.
[2] A stable atmosphere of gases inside the packaging can be achieved using active techniques, such as gas flushing and compensated vacuum, or passively by designing “breathable” films.
Jacques Étienne Bérard, a professor at the School of Pharmacy in Montpellier, France, reported delayed ripening of fruit and increased shelf life in low-oxygen storage conditions.
[4] Controlled atmosphere storage (CAS) was used from the 1930s when ships transporting fresh apples and pears had high levels of CO2 in their holding rooms in order to increase the shelf life of the product.
[5][8] In addition, it is also used to prevent oxidative rancidity in packaged products such as snack foods by displacing atmospheric air, especially oxygen, therefore extending shelf life.
[5][8] The use of noble gases such as helium (He), argon (Ar) and xenon (Xe) to replace N2 as the balancing gas in MAP can also be used to preserve and extend the shelf life of fresh and minimally processed fruits and vegetables.
[9] Its use results in a more stable red color of carboxymyoglobin in meat, which leads to another concern that it can mask evidence of spoilage in the product.
[5][9] Low O2 and high CO2 concentrations in packages are effective in limiting the growth of Gram negative bacteria, molds and aerobic microorganisms, such as Pseudomonas spp.
Therefore, lag phase and generation time of spoilage microorganisms are increased resulting in shelf life extension of refrigerated foods.
Microorganisms that can survive under low oxygen environment such as Campylobacter jejuni, Clostridium botulinum, E. coli, Salmonella, Listeria and Aeromonas hydrophila are of major concern for MA packaged products.
[7] Products may appear organoleptically acceptable due to the delayed growth of the spoilage microorganisms but might contain harmful pathogens.
[8] Flexible films are commonly used for products such as fresh produce, meats, fish and bread seeing as they provide suitable permeability for gases and water vapor to reach the desired atmosphere.
[6] Traditionally used packaging films like LDPE (low-density polyethylene), PVC (polyvinyl chloride), EVA (ethylene-vinyl acetate) and OPP (oriented polypropylene) are not permeable enough for highly respiring products like fresh-cut produce, mushrooms and broccoli.
MAP films developed to control the humidity level as well as the gas composition in the sealed package are beneficial for the prolonged storage of fresh fruits, vegetables and herbs that are sensitive to moisture.
[11] These types of machines are typically called pillow-wrap, which horizontally or vertically form, fill and seal the product.
This batch process is labor-intensive and thus requires a longer period of time; however, it is relatively cheaper than packaging machines which are automated.
Another method is purging the container from the bottom by gaseous carbon dioxide from a cylinder or bulk supply vessel.
