Electrophoretic techniques

Electrophoretic techniques are frequently used in species identification as a specific spectrum of soluble protein bands is produced for each animal species. Identification involves the use of homogenous gels, concentration gradient gels, pH gradient gels or denaturants such as urea or detergents that dissociate the tertiary protein structure. The band patterns in a supporting gel are visualized by simple non-specific staining or by enzymological or immunological methods. (Patterson, 1985). There are a number of electrophoretic techniques available:

• polyacrylamide gel electrophoresis (Anon, 1988b)

• isoelectric focusing (IEF) (Malmheden, 1986)

• sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) (Zerifi et al., 1991b and c)

A number of these methods have been used to identify meat species. IEF has been used to differentiate between species in raw meat (Skare et al., 1969; Bauer and Kelner, 1989). It has given good results with beef, pork, mutton, lamb, horse meat and venison (Anon, 1988a). It has also been used to distinguish poultry, game, goat, buffalo, deer and antelope (Collins, 1986; Jemmi and Schlosser, 1991; King and Kurth, 1982; Gleeson et al., 1983). SDS-PAGE can be used to differentiate meat from cattle, sheep, lamb, deer and rabbit (Kim, 1989).

Electrophoretic methods have also been applied to heated products but specificity can be poor in thoroughly cooked products. Quantitative results have been obtained for meat pie fillings and canned meat loaf which have been autoclaved at 1150C for 40min. This is possible by extraction in 8M urea and 1% 2-mercaptoethanol at 18-20oC for 16 h, followed by separation on gels containing 6% polyacrylamide (Guy et al., 1973; Connell, 1973; Anon, 1988a; Hofmann, 1988). IEF has also been used to detect one species mixed in another at levels above 20% in heated products (Jemmi and Schlosser, 1991). SDS-PAGE has also been shown to differentiate between species, even in mixtures (Zerifi et al., 1991a). If a large number of proteins are present, identification can be difficult as electrophoretic patterns are often complex and difficult to interpret. Positive identification in either of these techniques relies on the comparison of carefully selected sets of species-specific bands. This means that authentic control material is required for ultimate confirmation (Hofmann, 1989).

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