Cooking

Most meat products are consumed after they have been cooked. This can be done in water, oil, by hot air, infrared, or microwave energy. Cooking results in distinct textural changes in the meat due to denaturation of different muscle proteins. Three major phases can be observed during cooking. The first increase in toughness (45-55°C) is due to myosin denaturation, the second (60-70°C) is due to sarcoplasmic protein and some connective tissue denaturation, while the third (above 75°C) actually results in reducing the toughness, which is the result of collagen transformation into gelatin (13). Differences exist in the denaturation profiles of different meats, and various muscles within the same animal. An example of this is the higher rigidity developed in white poultry meat (or products containing white meat) as compared with dark meat (14).

Hot air ovens, with/without a smokehouse attached, are very popular in the meat industry. The meat products are placed in a chamber and the heat generated from a gas burner or an electrical element is transferred into the products. The amount of moisture in the air, air flow, and temperature difference between the product and air will determine the rate of heating. Of particular importance is the relative humidity in the air (expressed as amount of moisture in the air at a given temperature). Water is a good conductor of heat and its presence helps in delivering the heat; however, a moist product surface results in a cooling effect due to evaporation. Therefore, a balance between the two factors should be always maintained.

Cooking in Water. Cooking in water is a faster way of transferring the heat into the product compared with hot air. Steam kettles and water baths are used for this purpose. Commercial meat products are usually stuffed into a moisture-proof casing to eliminate cooking losses (consisting of protein, fat and moisture) from the product. However, some meat cuts are not packaged and are immersed directly in water/soup. This is done where moist heat is required to tenderize the tough connective tissue (eg, in boiling mature hen meat).

Frying. Frying is a very efficient way of transferring heat into the meat since the temperature of the fat can be raised well above 100°C. Frying in oil also provides a crisp texture on the outside of the product, which is desired in products such as fried chicken and breading on chicken nuggets.

Infrared Heating. Infrared heating is achieved by the use of an infrared lamp that heats up the surface of the product. The heat is then slowly transferred by conduction into the center of the product. This type of heating is mainly used for warming up cooked products, keeping products hot on a display counter, and in combination with microwave heating when surface browning is desired.

Microwave Heating. Microwave heating is a fast way of cooking whereby heating results from converting microwave energy to heat by friction of water molecules rotating due to rapid fluctuation in the electromagnetic field (915 and 2450 MHz are used commercially). Since cooking is very fast, there is usually not enough time to develop the typical brown color on the surface of the product. Therefore, other cooking methods, such as infrared, should be employed if a typical brown surface is required. Low microwave energy is also used to defrost meat. However, special care should be taken since there is a big difference between the heating profile of water and ice.

Smoking. Smoking is the application of wood-burning smoke compounds onto the product. Overall, more than 200 individual compounds have been identified in wood smoke (15). In the past, the only way of smoking was to expose the product to smoke derived from burning wood. Today, the processor can choose different preparations of liquid smoke extracts that can be directly added to the product, used as a dip, or be sprayed onto the product prior to cooking. In the past, smoking was mainly used as a means of preserving the meat that was also dried at the same time over wood fire. Some of the smoke components exert strong antimicrobial activity (eg, phenols) and therefore help in preserving the product. However, since these compounds can only penetrate a few millimeters into the product, they are basically protecting the surface. Today, smoking is mainly used to provide typical flavors to the product (eg, hickory smoke). The compounds that contribute to flavor include carbonyls, organic acids, and some of the phenols.

Smoking and cooking are considered to be two separate processes; however, they are usually discussed together because they often occur in immediate succession or simultaneously. It is important to realize that to achieve the best smoke penetration, the product should not be cooked because the denatured protein film, formed during cooking, will prevent smoke migration into the product. Therefore, smoking is done at low temperatures even though some heat is often applied to partially dry the surface. The latter is done to ensure that the smoke will not be washed off the product. When liquid smoke (smoke extracts) is used, the product is dipped or sprayed prior to cooking. In all cases, casings permeable to smoke (eg, collagen, cellulose) should be used. If liquid smoke is to be added directly into the raw batter, a special preparation (eg, pH adjusted) and low concentration should be used; and in this case there is no need to use permeable casings (9).

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