Evaluation of a commercial ELISA method for the quantitative detection of goat and cow milk in ewe milk and cheese

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 ELISA method, 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 cheese was 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 cow and 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.