The shelf-life of perishable foods as meat, poultry, fish, fruits and vegetables and bakery
products is limited in the presence of normal air by two principal factors-the chemical effect
of atmospheric oxygen and the growth of aerobic spoilage micro organisms. These factors
either individually or in association with one another bring about changes in odour, flavour,
colour and texture leading to an overall deterioration in quality. Chilled storage will slow
down these unde sirable changes but will not necessarily extend the shelf-life sufficiently for
retail distribution and display purposes.
The modified atmosphere concept for packaged goods consists of modifying the atmosphere
surrounding a food product by vacuum, gas flushing or controlled permeability of the packthus
controlling the biochemical, enzymatic and microbial actions so as to avoid or decrease
the main degradations that might occur. This allows the preservation of the fresh state of the
food product without the temperature or chemical treatments used by competitive preservation
techniques, such as canning, freezing, dehydration and other processes.
MAP is the replacement of air in a pack with a single gas or mixture of gases; the proportion
of each component is fixed when the mixture is introduced. No further control is exerted over
the initial composition, and the gas composition is likely to change with time owing to the
diffusion of gases into and out of the product, the permeation of gases in to and out of the
pack, and the effects of product and microbial metabolism (Church, 1994).
The normal composition of air is 21% oxygen, 78% nitrogen and less than 0.1% carbon
dioxide. Modification of the atmosphere within the package by reducing the oxygen content
while increasing the levels of carbon dioxide and/or nitrogen has been shown to significantly
extend the shelf-life of perishable foods at chill temperatures.