Yogurt samples purchased from a dairy industry, retail outlets, and hawkers in Lagos, Nigeria, were plated on potato dextrose agar containing 100 μg of chloramphenicol/ml and found to contain Candida lusitaniae, C krusei, C rugosa, Kluveromyces fragilis, and Saccharomyces cerevisiae as the primary yeast contaminants. Sixty-seven percent of the samples had yeast counts in the range of 104–106 cfu/ml. C. lusitaniae, K. fragilis and C. krusei had the highest counts and occurrence of 65, 48 and 51%, respectively, in 100 random yogurt samples. C. lusitaniae attained the highest count in yogurts stored at 10°C and C. krusei in those at 30°C.

Ninety percent of the samples had less than 10 coliforms or staphylococci per ml, whereas 20% had over 103 psychrotrophic bacteria per ml. Molds of Aspergillus sp. and Neurospora sp. were isolated mainly from the strawberry-fluid yogurt. The starter cultures, Lactobacillus bulgaricus and Streptococcus thermophilus, were present in the ratio of 1:1 and reached maximum growth levels of 107 to 108 cfu/ml after 4 to 8 d of storage at 10°C, whereas the yeast continued to increase beyond this level by the 12th day. The extent of contamination observed suggests high initial contamination level and improper refrigeration of yogurts marketed.

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Author notes

1Present address: Department of Biological Sciences, Rivers State University of Science and Technology, Port Harcourt, Nigeria.

2Present address: Department of Pathology, College of Health Sciences, University of Port Harcourt, Port Harcourt, Nigeria.