Enumeration and Identification of Yeast Species Isolated from Egyptian Soft White Cheeses and In Vitro Anti-yeasts Activity: A Preliminary Study.

Abstract

The aims of the current investigation were to enumeration and identification yeast species isolated from karish cheese and pickled Domiati cheese in order to study in vitro anti-yeast activity of some natural agents (natamycin and clove oil) and chemical agents (hydrogen peroxide and potassium sorbate) against yeast isolates to enhance the quality and safety of these products. The results showed that all karish cheese samples and 57% of pickled Domiati cheese samples were contaminated with yeasts above the limits required by the Egyptian standard, also karish cheese contained the highest total yeast count (Mean, 3.04 log cfu/g) in comparison to the examined pickled Domiati cheese (Mean, 2.7 log cfu/g). Twenty yeast isolates were obtained from cheese samples and identified by morphological, physiological and biochemical examinations, the colonies observed white, creamy and binky colors, and circular and irregular shapes. All of yeast isolates had inability to grow at 55°C and casein hydrolysis, however certain isolates exhibited the capability to ferment lactose and grow at a temperature of 7°C. The minimum inhibitory concentration (MICs) of natamycin, hydrogen peroxide and potassium sorbate for all yeast clusters were (0.5, 35, and 100 ppm) respectively, but for clove oil was ranged from 500 to 1000 ppm.