Fraud Identification of Undeclared Milk Species in Composition of Sheep Yogurt and Cheese Using Multiplex PCR Assay

Background: One of the adulterant practice in dairy industry is the use of a less costly type of milk such as cow and goat milk instead of more expensive ones especially sheep milk. The aim of the present study was to assess fraud identification of undeclared milk species in composition of sheep yogurt and cheese offered as “pure sheep” in Iranian local markets. Methods: Samples of sheep yogurt (n=40) and cheese (n=40) were purchased randomly from supermarkets in Ahvaz, Iran. According to the information provided by the vendors, all samples contained pure sheep milk. Using species-specific primers, a multiplex PCR assay was performed to detect the fraudulent addition of cow’s or goat’s milk into the sheep products. Results: In the molecular assay, the limit of detection of cow’s or goat’s milk in sheep yogurt was 2%, while this limit was 4% in sheep cheese. Only 27.5% of the yogurt samples and 20% of the cheese samples contained pure sheep milk. Adulterant presences of cow’s and goat’s milk were detected in 37.5% and 22.5% of the yogurt and 35% and 17.5% of the cheese samples, respectively. Conclusion: We showed high level of adulteration in the retail trade of sheep dairy products in Ahvaz, Iran. Therefore, continual surveillance on the production and sale of these products should be considered. Also, it was found that the multiplex PCR method used in this study is a useful and straightforward approach for the detection of low levels of cow’s or goat’s milk in sheep products.