AUTHOR=Desfossés-Foucault Emilie , Dussault-Lepage Veronique , Le Boucher Clementine , Savard Patricia , LaPointe Gisèle , Roy Denis 

TITLE=Assessment of Probiotic Viability during Cheddar Cheese Manufacture and Ripening Using Propidium Monoazide-PCR Quantification

JOURNAL=Frontiers in Microbiology

VOLUME=3

YEAR=2012

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2012.00350

DOI=10.3389/fmicb.2012.00350

ISSN=1664-302X

ABSTRACT=<p>The use of a suitable food carrier such as cheese could significantly enhance probiotic viability during storage. The main goal of this study was to assess viability of commercial probiotic strains during Cheddar cheesemaking and ripening (4–6 months) by comparing the efficiency of microbiological and molecular approaches. Molecular methods such as quantitative PCR (qPCR) allow bacterial quantification, and DNA-blocking molecules such as propidium monoazide (PMA) select only the living cells’ DNA. Cheese samples were manufactured with a lactococci starter and with one of three probiotic strains (<italic>Bifidobacterium animalis</italic> subsp. <italic>lactis</italic> BB-12, <italic>Lactobacillus rhamnosus</italic> RO011, or <italic>Lactobacillus helveticus</italic> RO052) or a mixed culture containing <italic>B. animalis</italic> subsp. <italic>lactis</italic> BB-12 and <italic>L. helveticus</italic> RO052 (MC1), both lactobacilli strains (MC2), or all three strains (MC3). DNA extractions were then carried out on PMA-treated and non-treated cell pellets in order to assess PMA treatment efficiency, followed by quantification using the 16S rRNA gene, the elongation factor Tu gene (<italic>tuf</italic>) or the transaldolase gene (<italic>tal</italic>). Results with intact/dead ratios of bacteria showed that PMA-treated cheese samples had a significantly lower bacterial count than non-treated DNA samples (<italic>P</italic> &lt; 0.005), confirming that PMA did eliminate dead bacteria from PCR quantification. For both quantification methods, the addition of probiotic strains seemed to accelerate the loss of lactococci viability in comparison to control cheese samples, especially when <italic>L. helveticus</italic> RO052 was added. Viability of all three probiotic strains was also significantly reduced in mixed culture cheese samples (<italic>P</italic> &lt; 0.0001), <italic>B. animalis subsp. lactis</italic> BB-12 being the most sensitive to the presence of other strains. However, all probiotic strains did retain their viability (log 9 cfu/g of cheese) throughout ripening. This study was successful in monitoring living probiotic species in Cheddar cheese samples through PMA-qPCR.</p>