The basic requirement for probiotic bacteria to be able to exert expected positive effects is to be alive; therefore, appropriate quantification methods are crucial. Due to disadvantages of conventional microbiological methods, the bacterial quantification based on the nucleic acid detection is increasingly used. The objective of this study was to evaluate the possibility to use propidium monoazide (PMA) in combination with real-time polymerase chain reaction (PCR) method or LIVE/DEAD BacLight viability kit in combination with flow cytometry (FCM) for determination of probiotic bacteria in a lyophilised product containing Lactobacillus acidophilus LA-5 and Bifidobacterium animalis ssp. lactis BB-12. In addition, the viability of probiotic bacteria in lyophilised product during 3 months storage was investigated. In the product, the results of real-time PCR quantification of PMA-treated cells did not differ significantly from those of non-treated cells, which indicate that most of the bacterial cells retained the membrane integrity although they have lost the culturability. The results obtained by FCM analysis were comparable with those by PMA real-time PCR. In conclusion, the PMA real-time PCR and FCM determination of the viability of probiotic bacteria could complement the plate count method which considers only the culturable part of the population.
Moisture content of solid-state pharmaceutical products is one of the main factors that affect drug stability, therefore suitable sorption studies need to be performed to assure drug quality throughout their shelf life. The Brunauer-Emmett-Teller (BET) and the Guggenheim-Anderson-de Boer (GAB) models are usually used for this purpose. Using gravimetrically obtained data, both methods were applied in the present work to evaluate the sorption characteristics of several excipients. Microcalorimetric analysis was also performed in order to evaluate the interaction between water and the substances. The results of these experiments show excellent agreement between data and the BET model up to 55% RH and the GAB model over the entire humidity range, confirmed by high values of the statistical determination coefficients. Furthermore, microcalorimetric measurements suggested that the hygroscopicity of solid materials could be estimated approximately using this approach.
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