Yeasts as Primary Contaminants in Yogurts Produced Commercially in Lagos, Nigeria

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.