Study on the prevalence of lipolytic yeasts and moulds in raw cow milk and white brined cheese

The extent of microbial contamination with moulds and yeasts of raw cow milk and white brined cheese produced in Bulgarian dairy enterprises was evaluated. The isolation and identification of microorganisms was performed using the classical microbiological methods. The samples of raw milk showed 76.6% contamination with moulds, at average amount of 3.4 log10 cfu/mL, maximum of 4.8 log10 cfu/mL. Yeasts were detected in 93.3% of the samples (average 3.5 log10 cfu/mL). Isolated moulds belonged to the genera Aspergillus (37.9%), Geotrichum (29.3%), Mucor (15.5%), Cladosporium (5.2%) and Penicillium (12.1%). Overall, 70% of studied samples were found to be contaminated with yeasts and moulds at 2.2 log10 cfu/g and 2.8 log10 cfu/g, respectively. Most commonly, isolates from white brined cheese were from the genera Geotrichum (32.8%), Aspergillus (28.1%), Mucor (21.8%) and Penicillium (9.4%). The predominating yeasts in raw cow milk and white brined cheese were Candida spp., Rhodotorula spp. and Sacharomyces spp. Isolates were tested for lipolytic activity on Tributyrin agar. The occurrence of lipolytic and toxigenic moulds and yeasts poses a risk for the quality and safety of milk and dairy products.