Enumeration of Yeasts in Dairy Products: A Comparison of Immunological and Genetic Techniques

Abstract

Enzyme-linked immunosorbent assay (ELISA) and PCR techniques have been developed for the detection of spoilage yeast species in dairy products. Polyclonal antibodies against live yeast cells (AY) were raised in rabbits by inoculation of a mixture of 10 yeast species frequently associated with dairy products spoilage. AY antibodies were used for the development of two ELISA formats (indirect and double-antibody sandwich ELISA) for the detection of yeast species in milk and yogurt. A PCR assay was also developed for yeast detection in dairy products, using primers designed to amplify a conserved 250-base pair fragment of the 18S rRNA of the yeast species. The results obtained in this work show that ELISA techniques using polyclonal antibodies against viable yeast cells are of limited value for the detection and enumeration of spoilage yeast species in dairy products. On the contrary, PCR amplification of a conserved region of the 18S rRNA of the yeast species allows the homogeneous detection of all the yeast species tested and, combined with an overnight enrichment of samples, could be used for the detection of low levels of viable spoilage yeast species in dairy products.