Control by Modified Atmosphere (or Reducing O-R Potential) ◾ 487
Gas Flushing
The gas-flushing method is used in both bulk and retail packages to increase the shelf life of many
refrigerated foods in European countries. In the United States, it is used in products, such as fresh
pasta, bakery products, cooked poultry products, cooked egg products, fresh and cooked fish and
seafood, sandwiches, raw meats, and some vegetables. The gases usually used are a mixture of
CO 2 and N 2 , with some O 2 for packaging red meats. Generally, the composition of gas mixtures
must be tailored for each product. In raw meats, a composition of 75% CO 2 , 15% N 2 , and 10%
O 2 was found to effectively prevent growth of Pseudomonas fragi for a limited period. Products
flushed with CO 2 alone were dominated by lactic acid bacteria, principally Leuconostoc spp. and
Lactobacillus spp. When N 2 and CO 2 were used together, along with lactic acid bacteria, Bro. thermosphacta, some coryneforms, and Enterobacteriaceae were also found. In the presence of some O 2 ,
lactic acid bacteria, Bro. thermosphacta, Enterobacteriaceae, and Pseudomonas spp. were isolated.
The product storage life, depending on a product, can be four weeks or more for fresh products
and eight weeks or more for processed products. 2,4
Conclusion
The use of a modified atmosphere to reduce the O-R potential of the environment has been a
very widely used method to control growth mainly of aerobic microorganisms in food. However,
facultative anaerobes and anaerobes can gain an advantage because of the absence of competition
from aerobes. They can also be controlled in an O-R potential–reduced food by combining other
methods, especially some chemical preservatives, which are discussed in Chapter 38.
QUESTIONS
1. Describe the methods used for the alteration of atmosphere to preserve foods.
2. Discuss the mechanisms of antimicrobial action in the MAP method used in foods.
3. Explain the different factors that can inhibit or influence microbial growth in a MAP food.
4. List the predominant microorganisms that can grow during the storage of vacuum-packaged
and gas-flushed packaged foods.
5. What is the major microbiological concern of MAP foods? How can this be solved?
6. Lis. monocytogenes has been implicated in foodborne disease outbreaks from the consumption of vacuum-packaged, refrigerated, low-heat-processed meat products. These products
are also spoiled (gas fermentation) by Leuconostoc spp. Briefly, discuss how these heatsensitive bacterial species can be implicated as a health hazard and spoilage in the properly
heated, packaged products. Also suggest a methodology to reduce the problems.
References
1. Church, I.J. and Parsons, A.L., Modified atmosphere packaging technology: A review, J. Sci. Food Agri.,
67, 143–152, 1995.
2. McMillin, K.W., Where is MAP going? A review and future potential of modified atmosphere packaging for meat, Meat Sci., 80, 43–65, 2008.
3. Artes, F., Gomez, P.A., and Artés-Hernández, F., Modified atmosphere packaging of fruits and vegetables, Stewart Postharvest Rev., 2, 1–13, 2006.
Gas Flushing
The gas-flushing method is used in both bulk and retail packages to increase the shelf life of many
refrigerated foods in European countries. In the United States, it is used in products, such as fresh
pasta, bakery products, cooked poultry products, cooked egg products, fresh and cooked fish and
seafood, sandwiches, raw meats, and some vegetables. The gases usually used are a mixture of
CO 2 and N 2 , with some O 2 for packaging red meats. Generally, the composition of gas mixtures
must be tailored for each product. In raw meats, a composition of 75% CO 2 , 15% N 2 , and 10%
O 2 was found to effectively prevent growth of Pseudomonas fragi for a limited period. Products
flushed with CO 2 alone were dominated by lactic acid bacteria, principally Leuconostoc spp. and
Lactobacillus spp. When N 2 and CO 2 were used together, along with lactic acid bacteria, Bro. thermosphacta, some coryneforms, and Enterobacteriaceae were also found. In the presence of some O 2 ,
lactic acid bacteria, Bro. thermosphacta, Enterobacteriaceae, and Pseudomonas spp. were isolated.
The product storage life, depending on a product, can be four weeks or more for fresh products
and eight weeks or more for processed products. 2,4
Conclusion
The use of a modified atmosphere to reduce the O-R potential of the environment has been a
very widely used method to control growth mainly of aerobic microorganisms in food. However,
facultative anaerobes and anaerobes can gain an advantage because of the absence of competition
from aerobes. They can also be controlled in an O-R potential–reduced food by combining other
methods, especially some chemical preservatives, which are discussed in Chapter 38.
QUESTIONS
1. Describe the methods used for the alteration of atmosphere to preserve foods.
2. Discuss the mechanisms of antimicrobial action in the MAP method used in foods.
3. Explain the different factors that can inhibit or influence microbial growth in a MAP food.
4. List the predominant microorganisms that can grow during the storage of vacuum-packaged
and gas-flushed packaged foods.
5. What is the major microbiological concern of MAP foods? How can this be solved?
6. Lis. monocytogenes has been implicated in foodborne disease outbreaks from the consumption of vacuum-packaged, refrigerated, low-heat-processed meat products. These products
are also spoiled (gas fermentation) by Leuconostoc spp. Briefly, discuss how these heatsensitive bacterial species can be implicated as a health hazard and spoilage in the properly
heated, packaged products. Also suggest a methodology to reduce the problems.
References
1. Church, I.J. and Parsons, A.L., Modified atmosphere packaging technology: A review, J. Sci. Food Agri.,
67, 143–152, 1995.
2. McMillin, K.W., Where is MAP going? A review and future potential of modified atmosphere packaging for meat, Meat Sci., 80, 43–65, 2008.
3. Artes, F., Gomez, P.A., and Artés-Hernández, F., Modified atmosphere packaging of fruits and vegetables, Stewart Postharvest Rev., 2, 1–13, 2006.