Industrial Applications

The visible gristle in meat is from a number of sources, including tendons (particularly from myotendon junctions), ligaments (such as the ligamentum nuchae in rib roasts), perimysium (particularly in the pennate extensors and flexors of the lower limbs), fasciae (such as the lum-bodorsal fascia of the longissimus muscle), and intramuscular vessels (particularly arteries). All these sources consist mainly of Type I collagen or elastin. Elastin-contained gristle retains its tensile strength after typical cooking procedures, such as roasting and broiling (11,12). Fresh meat cuts containing gristle are generally perceived as lower quality products, because of the unpleasant sensation of gristle. However, the elastin concentration is not consistently related to variations in the tenderness of muscles, at least in the bovine species (13), nor is the total concentration of connective tissue components (collagen and elastin). Tenderness is actually more related to soluble collagen and the overall fiber arrangement in the meat.

Aging is the industrial practice of storing meat carcasses above the freezing point for a certain period of time to improve the tenderness. The changes are the result of the physical breakage of muscle and collagen protein fibers by rigor and enzymatic reactions. However, aging has no apparent effect on the structure of elastin tissue and its physical properties.

Tissues with high elastin content, such as elastic ligaments, blood vessels, and lung, are removed in the slaughtering operation. They are processed as offals with other organs and by-products in the rendering industry as a protein source for animal feed. In this application, they may be rendered at high or low temperature, depending on the planned use of the fat. Fat is separated from the solids by centrifugation. The solids are dried and batched with other protein sources for optimum amino acid content and distribution, and then used in animal feed. The make-up of the feed is determined by a linear program based computer program which takes account of the amino acids, fat, carbohydrate, vitamin, and mineral content required in feed formulations.

In the ready-to-eat processed meat industry, elastin tissues and meat ligaments retain their tensile strength and are not gelatinized tinder most heat-processing conditions. For this reason, elastin tissues in meat are removed, with other gristle, by mechanical means, by hand or mechanical gristle removers. Grinders equipped with gristle and bone removers are widely used in the processed meat industry for coarse-ground, nonemulsified products. In this case, the meat is put through a grinder and the bone chips and gristle are separated from the ground meat. For large-muscle products, such as ham, the meat must be hand trimmed. The separated gristle with elastin and collagen tissue is discarded or chopped fine and used in emulsified products. It is used as a filler rather than functional proteins for economic reasons.

Meat cuts with a high gristle, collagen, and elastin content are not used in large-muscle products. They are used most often in emulsified products to minimize the toughness problem of the gristle. However, elastin and collagen tissues from gristle do not bind water or function as emul-sifiers in meat emulsion; therefore, emulsion breakdown occurs more often in these products. To solve these problems, a computer-based, least-cost formulations program, which is widely used in the processed meat industry, has incorporated the connective tissue in individual meat cuts as a quality constraint in the computer simulation of product formulations. But no effort has been made to separate the elastin or ligament contribution as a constraint in the computer program, because of the low content of elastin in most meat cuts.

Unlike collagen, elastin does not swell at mild acid conditions and has no film-forming properties. It is not used in gelatin production because of its poor water solubility and gelation properties. It cannot be substituted for collagen in regenerated collagen casing, or collagen film and tissue. Elastin also has little use in the processed meat industry because it functions poorly as a binder and emul-sifier. Because it is found in only small amounts in meats, because it is uneconomical to separate it from other meat tissues, and because it is poor nutritionally, elastin's technological development for use in foods and other industries has been hindered.

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