Prof. Dr. Mehmet Ali Kaşlıoğlu
(Food and Nutrition Science Expert)
Unpleasant metabolites like esters and thiols formed in meat are primarily breakdown products of proteins. When the microorganism count reaches 10^6 Kb/cm², spoilage begins in the meat. Spoilage caused by the formation of sticky secretions occurs when the microorganism count reaches approximately 10^8 Kb/cm². When the microorganism count reaches 10^9 Kb/cm², the meat surface is covered with a thick sticky layer. In meat that does not contain glucose, microorganisms start breaking down amino acids quickly, causing spoilage to occur faster. The spoilage in meat generally results in putrefaction, souring, and color changes.
Prevention of Spoilage
According to European Union directives, carcasses must be cooled to 7°C before being divided (cold splitting). At this temperature, carcasses are stored for 1-2 days after splitting. Typically, when hygienic conditions are met, the contamination level of the meat’s surface is low (10^3 Kb/cm² or less). Therefore, the microorganism count on the carcass surface should be less than 10^4 Kb/cm². The microorganism level after splitting varies depending on hygienic conditions (facility hygiene, staff hygiene, and equipment hygiene). The temperature in the splitting rooms is limited to a maximum of 12°C according to EU directives, and splitting should be completed in under 2 hours. This recommendation is particularly important for inhibiting the growth of Salmonella species during splitting when the central carcass temperature is reduced to 7°C.
One of the most important factors for the development of odors in meat is also the storage conditions. Meat that is not stored under proper conditions will spoil more quickly due to microbial growth. Microbial activity can also cause oxidation of fats, resulting in sour and bad smells. These odors are commonly described as rancid fat in beef and goaty smells in lamb. These odors become more pronounced during the cooking process.
Meat that is split under hygienic conditions at warm temperatures has a longer shelf life due to rapid cooling and the low number of psychrophilic microorganisms (cold-loving microorganisms). Psychrophilic bacteria are the main contributors to spoilage outside of normal cold storage periods.
Storage at Low Temperatures
The main purpose of cooling techniques is to slow down or limit the spoilage rate because temperatures below the optimal range can inhibit microbial growth. Low-temperature storage of meat is commonly done by “cooling” and “freezing.” These methods help prevent or completely stop bacterial growth.
Cooling
Meat is cooled in the range of 0–10°C. Cooling is used after slaughtering, during transport, and in storage. The carcass temperature must be reduced to 4°C within 4 hours after slaughter. Cooling is critical for hygiene, safety, shelf life, appearance, and nutritional quality of the meat. The surface temperature of the carcass drops faster with air cooling, improving drying and minimizing microbial spoilage.
Freezing
Freezing of meat occurs between -2°C and -20°C. The preservation capacity of frozen meat is limited because physical, chemical, or biochemical reactions in animal tissues do not stop after the cold process. Microbial growth stops at -12°C, and the total inhibition of cellular metabolism occurs below -18°C. Therefore, meat that will be stored for a period must be frozen at -20°C and stored below -18°C. Full quality changes in meat can be prevented at -55°C. However, enzymatic reactions, oxidative adjustments, and ice crystallization still play a significant role in spoilage. During freezing, approximately 60% of the microbial population dies, but the remaining population gradually increases during storage in the freezer. Frozen meat does not spoil but is never quite the same as fresh meat.
Key Considerations
When cooling and cold storage of meat:
- Meat must be cooled immediately after inspection, with the internal temperature of the carcass and meat pieces under 7°C, and internal organs under 3°C.
- Meat to be frozen must have an internal temperature of at least -12°C or lower and then stored below this threshold.
- Carcasses should be hung in cooling rooms so that they do not touch, allowing for proper air circulation.
- Frozen meat should be labeled with the freezing date.
