Validation of a rapid lateral flow method for the detection of cows' milk in water buffalo, sheep or goat milk.

For many years, the adulteration of milk from sheep, goats or water buffalos with cows' milk has been a widespread practice due to the higher cost of milk from those other species. Because of this, great concern has been shown by many Protected Designation of Origin councils that have to assure the quality and genuineness of the cheese produced by their associates. Therefore, the whole production chain needs analytical tools that allow the control of potential adulteration. Rapid methods to be used in the field are scarce and have not been validated according to international guidelines. The aim of this work has been to validate a rapid test based on lateral flow immunochromatography to detect cows' milk in milk from other species, including buffalo's milk, according to AOAC guidelines. No false-positive result was found after analysing 146 known negative samples from individual animals. The lowest level of adulteration with a Probability of Detection (POD) of 1.00 (confidence interval between 0.94 and 1.00) was found at 0.5% of cows' milk. This level is below the current EU allowed level of cows' milk, set at 1%. Variations in the time of assay, volume of the analysis buffer and different batches of the test were evaluated to detect any effect on the false-positive rate or on the limit of detection of the test. The effects of compositional factors (such as high level of fat, protein and somatic cell counts) were also evaluated. The new rapid test to detect cows' milk in milk from other species is shown to be an adequate tool to control milk quality in routine analysis. This kind of test is very easy to use and it can be performed by untrained staff during milk collection at the farm or upon arrival at dairies.