Assessing Viability and Stress Tolerance of Probiotics-A Review.

Ulrika Wendel

doi:10.3389/fmicb.2021.818468

Abstract

The interest in probiotics has increased rapidly the latest years together with the global market for probiotic products. Consequently, establishing reliable microbiological methods for assuring the presence of a certain number of viable microorganisms in probiotic products has become increasingly important. To assure adequate numbers of viable cells, authorities are enquiring for information on viability rates within a certain shelf-life in colony forming units (CFU). This information is obtained from plate count enumeration, a method that enables detection of bacterial cells based on their ability to replicate. Although performing plate count enumeration is one manner of assessing viability, cells can still be viable without possessing the ability to replicate. Thus, to properly assess probiotic viability, further analysis of a broader group of characteristics using several types of methods is proposed. In addition to viability, it is crucial to identify how well the cells in a probiotic product can survive in the gastrointestinal tract (GIT) and thus be able to mediate the desired health benefit while passing through the human body. A broad spectrum of different assay designs for assessing probiotic gastric tolerance have been used in research and quality control. However, the absence of any consensus on how to assess these qualities makes it difficult to compare between laboratories and to translate the results into in vivo tolerance. This review presents and discusses the complexity of assuring that a probiotic is suitable for beneficial consumption. It summarizes the information that can be subtracted from the currently available methods for assessment of viability and stress tolerance of a probiotic, hereby altogether defined as “activity.” Strengths and limitations of the different methods are presented together with favorable method combinations. Finally, the importance of choosing a set of analyses that reveals the necessary aspects of probiotic activity for a certain product or application is emphasized.

Highlights

To assure that a probiotic product contains an adequate number of live organisms, authorities are asking for information on viability rates within a certain shelflife in colony forming units (CFU) obtained from plate count enumeration (Hill et al, 2014; Fenster et al, 2019; Fiore et al, 2020; Hansen et al, 2020)
This review summarizes the information that can be subtracted from the currently available methods for determination of viability and stress tolerance of probiotics, here altogether defined as “activity”
Both viability and the ability to survive the passage through the human body and be able to give a beneficial health effect are altogether defined as probiotic activity

Summary

Introduction

The awareness of the health benefits of probiotic microorganisms, most often lactic acid bacteria (LAB), has increased rapidly the latest years and so has the global market for probiotic products (Rosenstiel and Stange, 2010; Hill et al, 2014; Hansen et al, 2018; Jackson et al, 2019; Fallico et al, 2020; Kiefer et al, 2020). The term probiotic is defined by FAO/WHO as “live microorganisms that, when administered in adequate amounts, confer a health benefit on the host” (Rosenstiel and Stange, 2010; Hill et al, 2014). To assure that a probiotic product contains an adequate number of live organisms, authorities are asking for information on viability rates within a certain shelflife in colony forming units (CFU) obtained from plate count enumeration (Hill et al, 2014; Fenster et al, 2019; Fiore et al, 2020; Hansen et al, 2020). Measuring CFU by plate count enumeration is one manner of detecting live cells, but viability is more complex than solely defined by the ability to form colonies

Methods

Findings

Conclusion