The document discusses various physical methods of food preservation, particularly focusing on modified atmosphere packaging (MAP), controlled atmosphere packaging (CAP), and vacuum packaging. These methods aim to control undesirable microorganisms and enhance the quality of food by altering storage atmospheres, thereby extending shelf life and maintaining freshness. Each method varies in application, cost, and effectiveness, specifically targeting different types of foods and microbial growth inhibition.

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Basura J Jayasundara
PHYSICAL METHODS OF FOOD PRESERVATION
Use of Modified Atmosphere in Food Preservation
Recently, modification of storage atmosphere to preserve foods has become one of the main
methods used most often. This may be due to the desire of consumers for fresh foods, foods with
less treatment and foods without preservatives. There are three methods used to alter the
atmosphere in foods in order to preserve and increase their quality.
 Modified Atmosphere Packaging (MAP)
 Controlled Atmosphere Packaging (CAP)
 Vacuum Packaging
The objectives above three methods are to control or reduce the undesirable microorganisms in
food. On the other hand these techniques help to retard enzymatic and respiratory activities of
fresh foods such as vegetable and fruits.
Modified Atmosphere Packaging (MAP)
MAP is consists of altering the chamber or package atmosphere by flushing with a gas mixture
usually containing combination of CO2, N2 and or O2. This method does not require a control of
the gaseous environment during the storage period. Optimum concentration of the gases used
varies with the type of food material. The composition of the gas atmosphere changes during
storage as a result of product and microbial respiration.
Carbon dioxide is included for its inhibitory effect, nitrogen is noninhibitory but has low water
solubility and can therefore prevent pack collapse when high concentrations of CO2 are used.
Controlled Atmosphere Packaging (CAP)
In this method, atmosphere of a storage facility or environment is altered and maintained
constant throughout storage period. It is used mainly for bulk storage and transport of foods,
particularly fruits and vegetables. This method is expensive method and used for long term
storage to maintain the freshness.
Vacuum Packaging
In recent years vacuum packing has been increasingly used for retail packs of products such as
cooked meats, fish and prepared salads

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Basura J Jayasundara
This method involves removal of air from the package, causing the bag to collapse around the
product before sealing, then sealing the package hermetically. To achieve the best results, it is
important to use the packaging material has a shape that allows the packaging film to collapse on
to the product surface entirely, without pockets and without the product puncturing the film.
Figure: Vacuum packed food products
Mode of action
The growth of aerobes (mold, yeast, aerobic bacteria) is prevented in products by primary
inhibition of microbial respiration. However, anaerobic and facultative anaerobic bacteria can
grow unless other techniques are used to control their growth.
In MAP and CAP have decreased O2 content and increased level of N2 and CO2 which retards
growth of many pathogens. In vacuum packing the O2 is removed so that aerobic bacteria cannot
grow but it does not prevent growth of anaerobes.
The inhibitory effect of CO2 on microbial growth occurs at the 10% level and increase with the
increase in concentration. In general, the Gram-negative bacteria are more sensitive to CO2
inhibition than Gram positives, with pseudomonads being among the most sensitive and
clostridia the most resistant. Microbial growth rate is reducing due to the following reasons.
 Rapid cellular penetration of CO2
 Alteration of cell permeability
 Interference of CO2 with several enzymatic and biochemical pathways

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Basura J Jayasundara
REFERENCES
 Adams, M.R., and Moss, M, O., 2008. Food Microbiology, third edition. RSC publishing,
UK.
 Ray, B., Fundamental Food Microbiology, third edition, 2004. CRC press.
 Jay, J.M., Loessner, M.J., and Golden, D.A., Modern Food Microbiology, seventh edition,
2005. Springer.
 Rahman, M.S., Handbook of Food Preservation, second edition, 2007. CRC press.
 www.fda.gov/Food/ResourcesForYou/Consumers/ucm261680.htm