SPECIES IDENTIFICATION IN DAILY PRODUCTS BY 3 DIFFERENT DNA-BASED TECHNIQUES

Polymerase chain reaction (PCR) with primers encoding a partial sequen ce of the beta-casein gene was performed to detect the corresponding D NA in milk and cheese after an adapted DNA extraction procedure. In th e PCR product from ovine or caprine beta-casein DNA was shown to conta in a specific restriction enzyme site that is not present in bovine be ta-casein DNA. Accordingly, after selected restriction enzyme analysis and horizontal polyacrylamide gel electrophoresis (PAGE), the undiges ted bovine beta-casein fragment can be detected as an additional band if cow's milk is present. Appropriate experiments using unprocessed mi lk demonstrated that a semi-quantitative assay could be established. T he detection limit was about 0.5% cow's milk in ewe's and goat's milk cheese. By use of a DNA intercalating agent the beta-casein PCR produc ts from cow or buffalo could be distinguished from those of ewe or goa t as a consequence of sequence-specific retardation during agarose gel electrophoresis. Furthermore, single-stranded conformation polymorphi sm (SSCP) analysis was applied to detect expected species-specific con formation of the selected beta-casein DNA sequences from the milk of c ows, ewes, goats and buffalos milk. These techniques are compared with respect to their special use and application.