From milk to diet: feed recognition for milk authenticity.

The presence of plastidial DNA fragments of plant origin in animal milk samples has been confirmed. An experimental plan was arranged with 4 groups of goats, each provided with a different monophytic diet: 3 fresh forages (oats, ryegrass and X-triticosecale) and 1 two week-old silage (X-triticosecale). Feed-derived rubisco (ribulose bisphosphate carboxylase, rbcL) DNA fragments were detected in 100 % of the analyzed goat milk samples and the nucleotide sequence of the PCR amplified fragments was found to be 100 % identical to the corresponding fragments amplified from the plant species consumed in the diet. Two additional chloroplast-based molecular markers were used to set up an assay for distinctiveness, conveniently based on a simple polymerase chain reaction. In one case, differences in single nucleotides occurring within the gene encoding for plant maturase K (matK) were exploited. In the other, plant species recognition was based on the difference in the length of the intron present within the trnL gene. The presence of plastidial plant DNA, ascertained with the PCR-based amplification of the rbcL fragment, was also assessed in raw cow milk samples collected directly from stock farms or taken from milk sold in the commercial market. In this case the nucleotide sequence of the amplified DNA fragments reflected the multiple forages present in the diet fed to the animals.