Fundamental Food Microbiology, Third Edition - Fuad Fathir

492 FUNDAMENTAL FOOD MICROBIOLOGY
processed products, originated in the early 20th century. During the 1920s and 1930s,
studies revealed that by using CO 2 in higher concentrations (4 to 100%), the growth
of molds on fresh meats could be greatly reduced and ripening of fruits and vegetables
could be prolonged. In the 1960s, refrigerated beef carcasses were transported
by ship from New Zealand and Australia to other countries in controlled CO 2-rich
environments.
In the 1960s, the availability of suitable plastic materials for packaging and the
necessary technology helped develop methods to preserve foods in different-sized
packages in an altered atmosphere. This was achieved either by vacuum packaging
or by gas flushing the package with one gas or a mixture of gases. During storage,
the gaseous environment could change because of the metabolic activities of the
food products and microorganisms and also to the permeability of gasses from the
air through the packaging materials. 1,2
In recent years, modification of the storage environment to preserve foods has
become one of the methods used most often. The desire of consumers for fresh
foods, foods that have been given less processing treatments and without undesirable
preservatives, as well as the availability of the necessary technology, have helped in
the economical production of many convenient and ready-to-eat foods that are
preserved by altering the environment. As the demand for such food is expected to
grow in the future, the use of an altered atmosphere to preserve these foods will
increase. 1,2
Three terminologies are used to alter the atmosphere in foods in order to preserve
and increase their acceptance quality. To avoid confusion, these terms are defined
here:
1. Controlled Atmosphere Packaging (CAP). In this method, the atmosphere in a
storage facility is altered and the levels of the gases are continually monitored
and adjusted as required. This is expensive to operate and used for long-term
storage of fruits and vegetables to maintain their freshness.
2. Modified Atmosphere Packaging (MAP). This method, unlike CAP, does not
require a high degree of control of the gaseous environment during the entire
storage period. In this method, a food is enclosed in a high gas-barrier packaging
material; the air is removed from the package, which is then flushed with a
particular gas or combination of gases; and the package is hermetically sealed.
3. Vacuum Packaging. This method involves removal of air from the package and
then sealing the package hermetically.
MAP and vacuum packaging have been described as two separate methods by some,
but as one method (e.g., MAP) by others. In this chapter, MAP has been used both
for vacuum packaging and gas-flush packaging.
II. OBJECTIVES
The objectives of MAP are to control or reduce the growth of undesirable microorganisms
in food. The technique also helps retard enzymatic and respiratory activities
of fresh foods. The growth of aerobes (molds, yeasts, and aerobic bacteria) is