ALCOHOL-MEDIATED HEMOLYSIS IN DAIRY YEAST ISOLATES AND HEMOLYTIC ACTIVITIES ON BLOOD AGAR MEDIA CONTAINING MILK AND CHEESE

摘要

Of a total of 143 presumptive yeast isolates obtained from Galician (north-west Spain) short-ripened raw cow's milk starter-free cheeses, 27 exhibited microbial alcohol-conferred hemolytic (MACH) activity. Among the MACH-positive isolates, eight were identified as Yarrowia lipolytica and four as Kluyveromyces lactis. These isolates of potential technological interest were subjected to spot agar assays on special blood agar media prepared with skim milk, whole milk and cheese. The hemolytic activities of the K.lactis isolates were generally more evident on skim-milk blood agar. However, the hemolytic activities of the Y.lipolytica isolates were strongest on whole-milk blood agar and cheese blood agar, and all of these isolates displayed total or predominantly beta-hemolysis reaction after 72-h incubation. Despite the fact that the MACH-positive yeast isolates assayed in the special media produce extracellular hydrolytic enzymes, particularly proteases and esterases, the hemolytic activity in these yeasts might be predisposed or triggered by environmental conditions which could be common in dairy products.