Detection of adulteration of sheep cheese (Lyghvan Brand) with cow's milk by a specific PCR method

By using molecular methods, e.g., polymerase chain reaction (PCR), it is possible to detect and differentiate the milks of closely related species (such as sheep and cow) in dairy products. The aim of the present study was to develop a specific PCR method for identification of cow's milk fraudulently used in making sheep cheeses (Lighvan Brand). Eighteen different samples of sheep cheeses (Lighvan Brand) claimed on the label to be 100% sheep cheese were collected from supermarkets in Tehran city. Total genomic DNA was extracted from all the samples. PCR was optimized for detection of specific cow's DNA in the sheep cheese samples based on amplification of mitochondrial cytochrome b gene (using the specific cytochrome b gene primer). The results were tested on a 2% agarose gel. Using the optimized PCR reaction based on amplification of the mitochondrial gene, 274 bp fragments of cow's DNA and 336 bp fragments of sheep’s DNA were obtained. The results demonstrated that cow's milk could be detected in 11 of the 18 brands tested. Thus, adulteration by the company was confirmed. The proposed PCR assay is a rapid, robust and reproducible method for the detection of adulterations in sheep cheese and other dairy products.