Prof. Dr. Mehmet Ali Kaşlıoğlu
(Food and Nutrition Science Expert)
Red meat and poultry obtained from slaughter animals intended for human consumption can be contaminated with microorganisms to a certain extent, depending on the hygienic conditions applied during production. Similarly, contamination of animal foods increases to varying degrees depending on post-production transport, processes applied at sales points, hygienic conditions, and storage conditions. To extend the shelf life of meat, cooling techniques are commonly used. However, in meat stored in cold conditions, some microorganisms continue to grow, and spoilage is inevitable after a certain period. If meat is not to be consumed shortly after purchase, it should be placed in the freezer. Meat kept in an environment other than the freezer can spoil after a short period.
Microbial Spoilage in Fresh Meat
In fresh meat, microbial spoilage typically begins when the total number of microorganisms in the meat exceeds 10^6 CFU (colony-forming units)/cm². The resulting spoilage appears as putrefaction and color change. Microorganisms are primarily responsible for spoilage, which manifests through the production of various metabolic products. Spoilage usually results in a) sticky secretion formation on the meat surface, b) color change, and c) the formation of undesirable odors. Spoilage generally starts on the meat's surface.
Color of Fresh Meat
Fresh meat has a red and bright appearance. The red color of meat is due to a protein called myoglobin. Myoglobin does not circulate in the blood but is stored in tissues with a purplish color. After meat is kept for some time, its color begins to turn purple, which is completely normal. However, this meat may have started to age. Nevertheless, meat of this color should never be discarded, as color change alone is not an indicator of spoilage. For fresh meat, color change is normal. Spoilage-induced color changes generally manifest as fading, darkening, or greening. Additionally, spoilage can cause odor, stickiness, and sludging in the meat. Fresh meat, with its bright appearance, will not stick to your hands.
Gray or Brown Color in Meat
Spoiled meat typically turns colors such as purple, green, or black, or local color changes may begin to appear. Meat stored in the refrigerator or freezer can darken or become lighter without immediately showing obvious changes. This alone does not mean the meat is spoiled. However, if a change in color is accompanied by a change in odor, then the meat has indeed spoiled. The myoglobin protein, which gives the meat its red color, is present in animal fibers and turns red when it comes into contact with oxygen, making red meat appear more appealing. If the meat is vacuum-sealed in the store, it may appear more purple. While this might not seem very appetizing, it is still quite healthy in this state. Once exposed to oxygen, myoglobin helps the meat take on a brighter red hue. After a while, the meat may turn a red-brown color, which does not indicate spoilage, as this is part of the natural process. The true spoilage process begins with putrefaction.
Spoilage Prevention
According to European Union directives, carcasses are cooled to a central temperature of 7°C before being cut (cold cutting). At this temperature, carcasses are stored for 1-2 days after slaughter. Hygiene is maintained during cutting, which results in a low level of contamination on the meat surface (below 10³ CFU/cm²). The microorganism levels on carcass surfaces must be below 10⁴ CFU/cm². The microbial levels after cutting depend on hygienic conditions, such as the hygiene of the facility, personnel, and equipment. Cutting rooms must maintain a maximum temperature of 12°C as per EU directives, and cutting should be completed within two hours to reduce the growth of potential Salmonella during the process.
Storage at Low Temperature
The main purpose of cooling techniques is to slow down or limit spoilage rates, as temperatures below the optimal range can inhibit microbial growth. Cooling and freezing are common methods for storing meat at low temperatures. Cooling is performed between 0-10°C, while freezing occurs between -2°C to -20°C. Frozen meat has limited preservation capacity, as physical, chemical, and biochemical reactions continue in animal tissues after slaughter. Microbial growth stops at -12°C, and the complete inhibition of cellular metabolism in animal tissues occurs below -18°C.
