Abstract :
Portugal produces traditional protected designation of origin (PDO) cheeses, being the
majority exclusively made with raw ewe’s milk.
A PDO cheese must be genuine, thus these products have to be controlled in order to
preserve its commercial quality. The possibility of adulteration of ewe cheesemilk with
cow or goat milk can result in inferior characteristics than that expected by the consumer.
The purpose of the present work was to evaluate and validate an available commercial
ELISAmethod, for quantitative determination of adulterations in ewe milk and cheese with
cow or goat milk. For this, ewe milk was mixed with cow and goat milk using a range
of adulteration percentages (1–50%) and model cheeses were manufactured according to
traditional Portuguese ewe milk cheesemaking. Ewe milk cheesewas also manufactured as
control. The milk samples and respective cheeses were analysed to detect and quantify the
amount of cow and goat milk added using specific commercial ELISA tests: Quantispeed
Bov Test: QBT® and Quantispeed Goat Test: QGT®, respectively.
Results obtained with QBT® and QGT® showed a correlation of ∼1 between the experimental
and the detected value. The method proved to be specific, precise and accurate
within the work domain and the detection and quantification limits were ∼0.2% adulteration
for both cowand goat milk. However, both tests revealed to be more accurate for milk
samples than for cheese samples. The detected value in cheese samples was ∼10% lower
than the experimental value for QBT® and ∼20% lower for QGT®, when more than 40% cow
or goat milk were added. Therefore, the use of this test is not adequate for routine surveillance
of cheeses in the market, especially for mixed cheeses, when the amount of milk from
different species used for cheesemaking is unknown.
