A study by five Italian researchers looked at three different modified atmosphere packaging (MAP) mixes to determine the best way to minimise microbial spoilage in refrigerated beef.
The MAP method is used to extend the shelf life of products by replacing the air in a package with a mixture of inert gases such as carbon dioxide and nitrogen. The low-oxygen mix extends the shelf-life of the meat, vegetables and other perishable foods by up to 15 days from the normal five days. The MAP method helps processors increase food safety and extend their markets.
In order to develop the right mix, processors need to consider a wide range of factors, including the food group and the type of machine and packaging being used.
The Italian scientists reported their findings in the July 2006 issue of the journal Applied and Environmental Microbiology.
"As far as we know, this is the first study to report the changes of spoilage-related microbial flora during storage of fresh meat," the researchers stated. "The assessment of microbial species diversity occurring in meat during storage and the study of the response and adaptability of the species to different antimicrobial conditions will be fundamental for improving and implementing packaging systems aimed a prolonging the shelf life of meat products."
Beef is one of the most perishable foods on the shelves. Spoilage - including oxidation and colour changes -- mainly occurs due to high water content and an abundance of surface nutrients.
In the study beef was packaged using three different MAP methods and stored at five degrees Celsius for fourteen days.
The first method consisted of normal air, the second of 60 per cent oxygen and 40 per cent carbon dioxide, and the third of 20 per cent oxygen and 40 per cent carbon dioxide.
While stored, the beef was monitored for viable counts of Pseudomonas, Enterobacteriaceae, Brochothrix thermosphacta, and lactic acid bacteria. The scientists also analysed the headspace gas composition, weight loss, and colour change over the period.
During the first seven days, the of 60 per cent oxygen and 40 per cent carbon dioxide mix offered the best protection against spoilage they found.
The mix helped maintain acceptable microbial loads and colour change, the scientists found.
Spoilage occur between seven and fourteen days and although many different genera and species were identified some were found more frequently and appeared to vary according to packaging conditions.
Rahnella aquatilis, Rahnella spp., Pseudomonas spp., and Carnobacterium divergens were prominent in the air packaging method. Pseudomonas spp. and Lactobacillus sakei were found in packaging high in oxygen content. Rahnella spp. and L. sakei were the main species identified during storage high in carbon dioxide, the study found.