Microflora of Austrian Natural-Set Yogurt

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Abstract
Randomly selected Austrian natural-set yogurts were examined for storage-induced changes in the populations of viable yogurt starter organisms and microbial contaminants. Typically, numbers of Streptococcus thermophilus and Lactobacillus bulgaricus remained above 108 cfu/g in yogurt stored at 10°C until the sell-by-date (15–20 d after manufacture). Both elevated storage temperature and storage periods markedly reduced the survival of yogurt starter bacteria. Depending on the sample origin, the yeast populations increased from less than 10/g to above 106/g when yogurts were stored at 10°C until the sell-by-date. The isolated yeasts were identified as Candida inconspicua, C. intermedia, C. parapsilosis, C. rugosa, C. tropicalis, C. zeylanoides, Debaryomyces hansenii, Metschnikowia reukauffii, Pichia guilliermondii, Rhodotorula mucilaginosa, Torulaspora delbrueckii, Trichosporon beigelii, and Yarrowia lipolytica. While a few out of 233 isolates were found to assimilate lactose, none were able to ferment lactose.