Often the level of yeast in raw milk is found to be 102-104 cells/ml (Lagneau et al. 1996; van den Tempel and Jakobsen 1998). The dominant yeast species detected in raw milk in Denmark, Italy, and Belgium were found to be C. famata, C. lipolytica, and Trichosporon cutanum (Corbo et al. 2001; Lagneau et al. 1996; van den Tempel and Jakobsen 1998). The study of raw milk in Belgium indicated that yeast count was depending on whether the milk came from cows with or without mastitis. Yeast were detected in more than 50% of samples from quarters with mastitis infections, but only in 25% of the samples from the noninfected quarters (Lagneau et al. 1996). Yeast have been detected in the number of 103cfu/ml in pasteurized milk (Fleet and Mian 1987; Lagneau et al. 1996; van den Tempel and Jakobsen 1998) and most of the common species in raw milk were able to grow to 108 or 109 cfu/ml in UHT milk even at low temperatures (Fleet and Mian 1987; Roostita and Fleet 1996b). Spoilage of raw milk and pasteurized milk by yeast are not reported as a very common problem. The occurrence of yeast in raw milk is assumed to be a contamination source of other dairy products. Reported investigations using molecular techniques to follow yeast at subspecies level through the whole production and to trace the origin of the yeast are limited.
In sweetened condensed milk the low water activity, due to high concentrations of sugar favor yeast as a potential spoilage organism while bacterial growth is inhibited. Yeasty taste and flavor and gas production are known spoilage by yeast in this product (Walker and Ayers 1970).
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