Characterization of butter spoiling yeasts and their inhibition by some spices.

:  This study was designed to identify the yeasts in packaged and unpackaged butters and screen antiyeast activity of spices, including marjoram (Origanum majorana L.), summer savory (Satureja hortensis L.), and black cumin (Nigella sativa L.) against the most dominant yeast species in the packaged and unpackaged butters. Mean total yeast populations were 5.40 log CFU/g in unpackaged butter samples and 2.22 log CFU/g in packaged butter samples, indicating better hygienic quality of packaged samples. Forty-nine yeast species were isolated and identified from butter samples with the most prevalent isolates belonging to genera Candida—C. kefyr, C. zeylanoides, and C. lambica—and with moderate number of isolates belonging to genera Cryptococcus, Rhodotorula, Saccharomyces, and Zygosaccharomyces. Black cumin exhibited the highest antiyeast activity against C. zeylanoides and C. lambica species, even inhibited these species, while summer savory inhibited C. kefyr. The results of this study revealed clear antimicrobial potential of black cumin against the yeast species isolated from butters. Marjoram, summer savory, and black cumin could be used as natural antimicrobial agents against spoilage yeasts in food preservation, especially in butter. Practical Application:  Yeasts are known to play an important role in the dairy industry for several reasons. They play an essential role in the preparation of certain fermented products and in the ripening of certain cheeses. Yeasts also can be used to ferment dairy products. However, yeasts are also known to cause spoilage of dairy and other food products. Spices have generally been considered as nonnutritive substances and their possible benefit to human health has recently been considered. In addition, spices could perform different antimicrobial activities on pathogenic and food spoilage yeasts. For this purpose, this study was designed to cover the following items: (1) enumeration of the yeast populations in packaged and unpackaged butter samples; (2) isolation and identification of the yeast species to characterize the yeasts of the butter samples; (3) screening of antiyeast activity of these spices against the most dominant yeast species, Candida kefyr, C. zeylanoides, and C. lambica, in the packaged and unpackaged butter samples.