Polyclonal antibodies with predetermined specificity against bovine αs1-casein: application to the detection of bovine milk in ovine milk and cheese

Comparing the primary sequences of bovine and ovine milk proteins, some short peptide fragments are cow-specific, in particular the 141-148 fragment of bovine alpha s1-casein, which is deleted in its ovine counterpart. The 140-149 peptide was chemically synthesized on a solid phase matrix and directly used as an immunogen to produce polyclonal monospecific antibodies in rabbits. These antibodies recognized this fragment both on the peptidyl resin and in the native protein. They appeared to be monospecific, since no antigen-antibody complex was formed with homologous ovine or caprine proteins. Subsequently, a competitive enzyme-linked immunosorbent assay was successfully developed for the detection of defined amounts of cows' milk in sheep's milk from 0.125 to 64% (v/v) and in cheese from 0.5 to 25% (v/v) that was not influenced by heat treatment of milk or the degree of ripening of cheese.