Animal Fats and Oils
Animal Fats and Oils
natural products obtained from the fatty tissues of animals and consisting of mixed triglycerides of saturated or unsaturated fatty acids, the composition and structure of which determine the basic physical and chemical properties of the fats and oils.
If saturated fatty acids predominate, animal fats have a solid consistency and a comparatively high melting point (see Table 1). Such fats are present in the tissues of land animals (for example, beef and mutton fats). Animal fats and oils are part of the makeup of the tissues of marine mammals and fish and the bones of land animals. A characteristic of fats and oils of marine mammals and fish is the presence of triglycerides of highly unsaturated fatty acids (with four, five, or six double bonds). The iodine numbers of such fats and oils are between 150 and 200. Milk fat occupies a special place among the animal fats, ordinary butter containing as much as 81–82.5 percent, and cows’ milk, 2.6–6.0 percent milk fat. Milk fat contains up to 32 percent oleic acid, 24 percent palmitic acid, 10 percent myristic acid, and 9 percent stearic acid, as well as other acids, constituting as much as 98 percent of the total fat content.
|Table 1. Composition and properties of domestic-animal fats.|
|Factor||Beef fat||Mutton fat||Pig fat|
|Fatty acid content, in percent Saturated:|
|Density at 15°C, kg/m3||937–953||937–961||915–923|
|Melting point, °C||42–52||44–55||30–44|
|Solidification point, °C||34–38||34–45||22–32|
|Calorific value, joules/kg (kcal/100g)||3980 x 104 (950.5)||3956 x 104 (944.9)||3981 x 104 (950.9)|
|Assimilability, in percent||80–94||80–90||90–98|
In addition to triglycerides, animal fats contain glycerol, phosphatides (lecithin), sterols (cholesterol), lipochromes, which are coloring matters (carotene and xanthophyll), and vitamins A, E, and F. Marine mammal and fish liver oils are particularly rich in vitamin A. Milk fat also contains vitamins K and D. Water, steam, acids, and enzymes (lipases) readily hydrolyze animal fats to free fatty acids and glycerol. Treated with alkalies, fats form soaps.
In the body, animal fats act as reserve material, utilized when nutrition deteriorates, and protect the internal organs from cold and mechanical effects.
Animal fats are most widely used as food products. The important food fats, beef and mutton fats and lard, are obtained from the fatty tissues of cattle and swine. Food, medicinal, and veterinary (feed) fats and industrial fats and oils are prepared from the tissues of marine mammals and fish. Food fats, hygrogenated to margarine, are produced from adipose tissues of whalebone whales (seis, finbacks). Medicinal fats, containing vitamin A and used in therapeutic and prophylactic preparations, are made from gadid (cod, haddock, saury) livers. Veterinary fats are added to the feed of agricultural animals and poultry and are made from the tissue and liver fats of fish and marine mammals. Industrial fats and oils are used in light industry, the chemical and perfume industries, and other branches of the national economy to treat leather and to make detergents, antifoaming agents, and various creams and pomades. Industrial fish oil is primarily a by-product of feed production, made from the various wastes (heads, bones, entrails, and fins) of substandard fish and fish of little food value and from substandard raw materials in processing whalebone whales and pinnipeds. The fats of toothed whales (mainly sperm whales), the high wax content of which renders these fats unsuitable for food, are also used industrially.
Animal fats are isolated from adipose tissue and separated from proteins and moisture by heating above the melting point. The fats are melted out from the chopped tissue in open cookers; unchopped tissues are treated in autoclaves under pressure. Continuous-action assemblies are used extensively in rendering food fats and others. They include the AVZh (USSR), the Titan (Denmark), and the De Laval (Sweden). It takes between seven and ten minutes in these plants from the time the raw material is loaded to the finished product. Rendering fats with a continuous-flow AVZh plant, which is extensively used in the meat industry, involves the following stages: The raw material is loaded into the funnel of a centrifugal device, where knives mince it and it is heated by steam to 85°-90°C. The fatty material obtained is sent via a feed tank to a horizontal centrifuge to separate the proteins from the fat and water. The fat and water go through another centrifuge to a second feed tank and thence to separators for refining (two or three times). By means of a third centrifuge, the clear fat is sent to a receptacle, from which it goes to a coil apparatus to be cooled to 35°-42°C. In the last step the fat is sent for bottling and packing.
REFERENCELiberman, S. G., and V. P. Petrovskii. Spravochnikpo proizvodstvu zhivotnykh zhirov, 3rd ed. Moscow, 1960.
V. P. PETROVSKII and K. A. MROCHKOV