Differentiation techniques of meat of different animals

Histological techniques: In this technique we generally measured muscle fiber length, diameter, density and pattern of the muscle fibers in different meats of animal origin. The muscle fiber diameter of beef is larger than that of buff but the number of muscle fibers/mm2 in beef is less than that of buff. Similarly, in case of muscle striations beef meat is less angular than that of buff.

Chemical techniques: For meat species specifications various chemical tests are of immense value. In these tests we can easily estimate the amount of certain chemicals presents in the meat of different animal species (Thornton, 1968). On the basis of its contents present in particular meat we can easily get an idea about the meat species. On table no. 2 above there are chemical characteristics of different types of meat.

Biological techniques: These techniques are mainly based on the principles of antigen antibody reactions. The homologous antigen binds with the antibody which is visualized by various methods. These techniques are simple and can be performed anywhere with little efforts. These tests are also known as Serological or Immunological methods.

Precipitation test: It is also known as Ring Precipitation Test (RPT) in which homologous antigen and antibodies reacts together and make a ring at the point of its interaction. Known antibodies (blood serum) collected from the treated experimental animals are mixed in a test tube with the filtered extract of meat samples. If precipitation line forms at the point of mixing then it indicates positive test. For example, if the antiserum of horse mixed with filtered extract of suspected meat in a test tube, a turbidity occurs and forms a definite precipitation ring if sample is positive for horse flesh. It has some limitations such as, this test can apply only for qualitative evaluation; cannot apply for heat treated meat. It gives false positive test in closely related species due to cross reactivity. In this technique developed ring is difficult to observe and diffused in a short period of time.

Complement fixation test (CFT): CFT is also known as Immunodiffusion Test or Agar Gel Precipitation Test (AGPT) or Agar Gel Immunodiffusion Test (AGID). The principle of test is same as in precipitation test but a compliment is used to reproduce the results for longer duration.

Overnight rapid identification tests: These tests are Overnight Rapid Beef Identification Test (ORBIT) or Poultry Rapid Overnight Field Identification Test (PROFIT) or Multispecies identification field test (MULTI-SIFT) or Dot-blot technique. In these tests three disks, i.e., blank, disk with beef or poultry antigen and disk with bovine or poultry antiserum are generally used. The sample fluid is filled in blank disk and directly placed in precast agar gel and allow it to incubate overnight and then observed for precipitation development. This test can also be used for multispecies by using Multispecies identification field test (MULTI-SIFT). This modified test can be used for beef, pork, poultry, sheep, horse and deer meat. Another similar test is Dot-blot technique in which binding of antigen from the sample is take place in a membrane (nitrocellulose or cyanogen bromide activated nitrocellulose) with a specific antibody.

Enzyme-linked immunosorbent assay (ELISA): It is a rapid, highly sensitive (able to detect 2% adulteration) and most suitable method for handling numerous samples at a time. There are several ELISA techniques are in use depending on the compound fixed, solid support used and concentrations of antigen and antibodies used such as Indirect ELISA, Competitive ELISA and Sandwich ELISA (Patterson and Spencer, 1985)

Electrophoresis techniques: These techniques are based on the separation of proteins by their differential migration through a supporting medium under the influence of electric field (Kim and Shelef, 1986). The protein bands thus resolved are visualized by general, enzymological, chemical or immunological means.

Poly acrylamide gel electrophoresis (PAGE): Initially disc electrophoresis in polyacrylamide gel was used for meat protein separation on the basis of total protein pattern of different meats. A simple visual differentiation without staining of the species is generally practiced to compare the respective migration rates of the brownish myoglobin bands.

Sodium Dodecyl Sulphate PAGE (SDS-PAGE): SDS-PAGE is a variant of PAGE is commonly used for separating protein subunits and determining their molecular weights. On heating, polypeptides dissociate and when these polypeptides bind with SDS in the presence of reducing agent 2-mercaptoethanol forms SDS-polypeptides. When this complex is subjected to a sieving polyacrylamide gel, migrate according to the molecular weights of the polypeptides. PAGE-SDS (pH 3-10) can be utilized for identification of beef, mutton, venison, rabbit meat and raw and cooked crustaceans. It is a suitable method for heated meat samples up to 100°C beyond which most of the protein bands disappears. This is a good technique for closely related meat species and has good resolution and reproducibility.

Polymerase Chain Reaction (PCR): PCR is a rapid method because in this technique we can obtain multiple copies of specific piece of DNA sequence in vitro and it has high degree of selectivity and sensitivity. PCR amplifies a target DNA sequence in an exponential phase, being capable of detecting even a single copy sequence from a single cell sample. It is a qualitative test for meat species specification. There are two main techniques for amplification of genetic marker, i.e., mono-locus-specific primers for amplification of a concrete DNA fragment and multi-locus amplification of non-targeted DNA. By this technique closely related meat species can be identified with the discrimination between male and female raw meat.