Fundamental Food Microbiology, Third Edition - Fuad Fathir

CONTROL BY MODIFIED ATMOSPHERE (OR REDUCING O–R POTENTIAL) 495
A. Vacuum Packaging
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V. METHODS
Vacuum packaging is predominantly used as retail packs in many fresh and readyto-eat
meat products, including beef, pork, lamb, chicken, and turkey. Red meat,
due to change in color to purple (reduced myoglobin), is not very popular with
consumers. The refrigerated storage life of these products varies greatly: ca. 3 to 4
weeks in fresh meat and as long as 8 weeks or more in processed meats. If the
products have low A w or low pH, or both, are produced under sanitary conditions,
and kept at temperature ca.1.5ºC, the storage life can be much longer. In low-pH
products, Leuconostoc spp. and Lactobacillus spp. usually predominate, whereas in
high-pH products, Bro. thermosphacta, Serratia liquifacience, and Hafnia spp. are
isolated, along with lactic acid bacteria. In fresh beef and pork and roasted beef,
psychrotrophic Clostridium spp. have also been found to grow, even at temperatures
below –1ºC. Vacuum packaging is also used in different types of cheeses, sausages,
and low-pH condiments to control growth of yeasts and molds. 2–6
B. Gas Flushing
The gas-flushing method is used in both bulk and retail packs to increase the shelf
life of many refrigerated foods in European countries. In the U.S., 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 4 weeks or more for fresh products
and 8 weeks or more for processed products. 2–6
VI. CONCLUSION
The use of modified atmosphere to reduce 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 37.