Increased sensitivity for detection of specific target DNA in milk by concentration in milk fat

A protocol for DNA extraction from whole milk, milk fat, skim milk and milk sediment was developed for detection of foreign DNA in milk. The isolated DNA from the different fractions of raw milk was quantitated yielding a 20:40:40 (cream: sediment: skim milk) percent ratio. Raw milk samples were spiked with genomic soya DNA and the detectability of an internal 118-bp fragment of a soya lectin gene was determined by PCR amplification. Added soya DNA was found distributed in the cream and skim milk fractions, with best detectability in the cream fraction. By increasing the sample volume from 1 ml to 100 ml raw milk the detection limit was improved from more than 1ng genomic soya DNA per ml raw milk to 0.01 ng/ml.