Contaminating Mycoflora in Yogurt: General Aspects and Special Reference to the Genus Penicillium

A microbiological study was carried out on three commercial brands of yogurt with three different flavors. Each sample was divided into two lots, one for initial analysis and the other was stored at 4°C for 20 d before analysis. The lots were denominated initially and at the end of storage. Frequency of appearance in integrating the genera of the mycoflora of yogurt was observed to be very different, which enabled us to establish two types of flora: normal and sporadic/infrequent. We considered the mycoflora belonging to the genera Penicillium , Monilia , Cladosporium , Micella sterilia , Alternaria , Rhizopus , Aspergillus and yeasts in general to be normal. The genera considered to be sporadic totaled seventeen. From the count of toal colonies of molds per ml, it was deduced that the quantitative method is not valid for this type of microorganism in yogurt. Culture media used showed similar levels of effectiveness for growth of the various genera. The comparative study conducted on the two lots, initial and final, showed a certain evolution of mycoflora present in the product. With regard to the Penicillium genus, the highest frequencies of appearance occurred in the same brand and in both lots. Comparing the results according to flavor, differences were found between initial and final lots. Malt extract agar was the most favorable culture medium for development of the Penicillium strains isolated for yogurt. As to species, the presence of Penicillium frequentans is to be noted because of its possibly toxigenic nature.