Acid and bile stability and intestinal mucosal
adhesion properties are among the criteria used to select probiotic
microbes. The quality control of probiotic cultures in foods traditionally
has relied solely on tests to ensure that an adequate number
of viable bacteria are present in the products throughout their
shelf lives. Viability is an important factor, but not the only criterion
for quality assurance. To be effective, probiotic strains must
retain the functional health characteristics for which they were
originally selected. Such characteristics include the ability to survive
transit through the stomach and small intestine and to colonize
the human gastrointestinal tract. In vitro test protocols can be
readily adopted to examine the maintenance of a strain’s ability to
tolerate acidic conditions, survive and grow in the presence of bile,
and metabolize selective substrates. Molecular techniques are also
available to examine strain stability. Adhesion characterization
may be an important quality-control method for assessing gut barrier
effects. Adhesion has been related to shortening the duration
of diarrhea, immunogenic effects, competitive exclusion, and
other health effects. Adhesion properties should be carefully monitored,
including adhesion to intestinal cells (eg, Caco-2) and
human intestinal mucus. This article outlines the types of in vitro
testing that can be used to ensure quality control of functional probiotic
strains. Am J Clin Nutr 2001;73(suppl):393S–8S.