Meat processing involves the slaughter of animals and fowl, processing of carcasses into cured, canned, and other meat products, and rendering inedible and discarded remains into useful by-products such as lards and oils. Meat undergoes a wide range of processes, including curing or preserving techniques such as salting, wet pickling, drying, cooking, canning, sausage manufacture, and ham curing.
These processing techniques aim to inhibit microbial spoilage and increase the shelf life of meat. Major principles in meat processing include the use of heat, low temperature, smoking, modified atmosphere packaging, and ionizing radiations.
Preservation methods are mainly grouped into three categories: control by temperature, by moisture, and by lethal agents (bactericidal, fungicidal, etc.).
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Preservation Techniques for Meat
1. Use of Low Temperatures in Meat Preservation
Chilling and freezing are the most commonly used preservation systems for meat and meat products.
i. Chilling
Chilling is the most widely used technique to preserve raw and processed meat. Chilling preserves muscle tissue by retarding the growth of microorganisms and slowing many chemical and enzymatic reactions. Storage temperature may vary from -1.4 to 2.2°C for storage of beef for 30 days, depending on the number of microorganisms.
ii. Freezing
Freezing is an excellent process for preserving the quality of meat for long periods. Freezing is often used to preserve meats during shipment over long distances or for extended storage. When the storage temperature is below -18°C, changes occur at a very slow rate in the muscle of warm-blooded animals. The quality of frozen meat depends on various factors such as the rate of freezing, packaging, etc.
2. Use of Heat in Meat Preservation
The canning of meat is a specialized technique, as the procedure varies considerably with the meat product to be preserved. Since meat products are low-acid foods, the rate of heat penetration is fairly low. Commercially canned meats can be divided into two groups based on the heat processing used:
- Meats that are heat-processed to make the can contents sterile.
- Meats that are heated enough to kill part of spoilage organisms but must be kept refrigerated to prevent spoilage.
3. Dehydration for Meat Preservation
Deprivation of available moisture (reduction of water activity) for microbes not only prevents their growth but also kills them, resulting in increased shelf life and better quality product. Drying meats can be successfully employed for both raw and cooked meat. Texture is most severely altered by dehydration. The tough texture of dehydrated meat can be overcome by preparing products with intermediate levels of water. Drying can be done under the sun or with ovens.
4. Smoking as a Meat Preservation Method
Smoking is often used with salting and curing. It gives desired flavor, aroma, and aids in preservation. Preservative substances added to the meat, together with the action of heat during smoking, have a germicidal effect, and drying of the meat, combined with chemicals from the smoke, inhibits microbial growth during storage.
Smoke consists of phenols, alcohols, organic acids, carbonyl compounds, and hydrocarbons. The desirable effects of smoking meat include:
- Meat preservation through aldehydes, phenols, and acids (antimicrobial effect).
- Antioxidant impact through phenols and aldehydes (retarding fat oxidation).
- Smoke flavor through phenols, carbonyls, and others (smoking taste).
- Smoke color formation through carbonyls and aldehydes (attractive color).
- Surface hardening of sausages/casings through aldehydes (for a more rigid structure of the casing).
Alternative Methods for Meat Preservation
1. Modified Atmospheric Storage for Meat
Fresh meat held at refrigerated temperatures has a limited shelf life due to microbial growth. Modified atmosphere refers to the adjustment in the composition of the atmosphere surrounding the product.
At higher concentrations of CO2, surface browning of meat occurs due to the oxidation of myoglobin and hemoglobin pigments to the ferric state. The most desirable concentration of CO2 in a modified atmosphere is a compromise between bacterial inhibition and product discoloration.
2. Ionizing Radiation for Meat Preservation
Ionizing radiation is a potentially useful form of preservation. Besides its desirable ability to inactivate microorganisms, it also has the undesirable effect of altering meat pigments. Radiation for food treatment is achieved through the application of gamma rays (with Co-60 or Cesium-137 radioisotope), electron beams (high energy of up to 10 MeV), or X-rays (high energy of up to 5 MeV).
Sterilizing doses of ionizing radiation result in the breakdown of various lipids and proteins, leading to often undesirable odors. Tenderization of muscle may also occur during this treatment. Temperatures of ≤80°C or below greatly reduce undesirable effects without affecting the lethal effect on microorganisms.
Generally, enzymes are not inactivated by irradiation treatment, so it is necessary to heat to approximately 70°C prior to irradiation and storage. The safety of irradiated foods for human consumption has been questioned because ionizing radiation can lead to chemical changes.
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Processing Meat into Various Products
1. Comminuted Meat Products
Comminution is the mechanical process of reducing raw materials to small particles, known as minced meat.
i. Sausages
Sausages are usually defined as comminuted seasoned meats stuffed into casings; they may be smoked, cured, fermented, and heated. They are made from any edible part of the slaughtered, veterinary-inspected animal and a series of non-meat ingredients.
Sausages are meat products that are salted, usually seasoned or spiced, and are examples of comminuted meat products generally recognized as emulsified, stuffed, linked, smoked, and cooked meat products.
Based on product characteristics and processing methods, they are broadly divided into three categories: fresh sausages, cured sausages, and fermented sausages.
ii. Cured Meat Products
Curing of meat involves the addition of sodium chloride, sodium nitrite, or sodium nitrate and adjuncts to meat to increase shelf life and obtain desirable color and flavor. Sugar may or may not be added along with other ingredients to improve flavor.
Curing can be done for both raw/cooked meat cuts and comminuted meat products, such as sausages and similar preparations. The most popular raw cured meats include ham and bacon, which are pork products. However, the technique can be applied to any meat group.
iiii. 2. Ingredients Used in Curing
The use of nitrite in cured meat may be hazardous if used at higher concentrations with improper mixing, as it reacts with amines, especially secondary amines, to form N-nitrosamines, which may be carcinogenic. High temperatures may also induce nitrosamine formation.
3. Indigenous Meat-Based Products in Nigeria
Suya (a Hausa word for “to fry” or “fried meat”) is an intermediate-moisture meat product that is easy to prepare and highly relished. Suya is a popular, traditionally processed, ready-to-eat Nigerian meat product, originally produced from beef and later extended to other ruminant animals.
In recent years, non-ruminant animals are being utilized in suya making. Suya and kilishi are made by roasting spiced, salted slices/strips of meat (usually beef). Kilishi differs from suya in that a two-stage sun-drying process precedes roasting. Consequently, kilishi has a much lower moisture content (6-14%) than suya (25-35%).
Dambu-nama is a Nigerian traditionally spiced, cooked, pounded, shredded, and dried meat product commonly obtained using beef, goat meat, mutton, or camel meat and is popularly consumed in the northern parts of Nigeria. The product appears to have developed as a means of preserving meat in the absence of refrigerated storage by early Fulani and Hausa herdsmen.
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