Application of propidium monoazide coupled with quantitative PCR to evaluate cell viability of Bifidobacterium animalis subsp. lactis in a non-dairy probiotic beverage

Purpose In this study, a PMA-qPCR assay was developed for the enumeration of Bifidobacterium animalis subsp. lactis BB-12 viable cells in a non-dairy probiotic beverage. Methods Probiotic viability was monitored in three formulations of probiotic passion fruit juice microencapsulated by spray drying, during 30 days of storage at 4 degrees C. Viable cells were quantified using qPCR and PMA-qPCR assays targeting tuf gene and by plate counting method. Results The limit of detection for all samples was 10(3) genome copies, corresponding to 21.3 pg of DNA. Higher CFU values were obtained for B. lactis BB-12 enumeration by qPCR, when compared to those obtained by PMA-qPCR and plate count, for all probiotic juice microcapsules. Similar quantification values were obtained by PMA-qPCR and plate counting for all samples and remained above 8 log CFU/g during the storage period. Conclusion These results demonstrated that the PMA-qPCR technique is a promising approach for B. lactis BB-12 viable cell enumeration in complex matrices such as passion fruit juice microcapsules. This PMA-qPCR assay allowed the achievement of reliable results faster than with the traditional plate counting method.