Viable cells differentiation improves microbial dynamics study of fermented milks

Understanding the changes that occur during storage of fermented milk products is of significant importance to dairy producers. Here, we investigated the microbiota dynamics of two fermented milk products, yoghurt and kefir, using culture-independent methods in combination with the use of a viability dye and quantitative-polymerase chain reaction. Propidium monoazide (PMA) was used to selectively detect viable cells in the food matrix. Samples treated with PMA showed results comparable with culturing methods and a lower copy number than samples not treated with PMA. The use of two culture-independent approaches combined with PMA treatment showed a more complete picture of the viable microbiota in the fermented milks during storage. Significant differences in microbiota were detected in kefir samples treated with and without PMA whereas no such significant differences were found in yoghurt. The microbiota in kefir also showed a high variation between batches at the species level.