Quality assurance criteria for probiotic bacteria

Acid and bile stability and intestinal mucosal adhesion properties are amon g the criteria used to select probiotic microbes. The quality control of pr obiotic cultures in foods traditionally has relied solely on tests to ensur e that an adequate number of viable bacteria are present in the products th roughout their shelf lives. Viability is an important factor, but not the o nly criterion for quality assurance. To be effective, probiotic strains mus t retain the functional health characteristics for which they were original ly selected. Such characteristics include the ability to survive transit th rough the stomach and small intestine and to colonize the human gastrointes tinal tract. In vitro test protocols can be readily adopted to examine the maintenance of a strain's ability to tolerate acidic conditions, survive an d grow in the presence of bile, and metabolize selective substrates. Molecu lar techniques are also available to examine strain stability. Adhesion cha racterization may be an important quality-control method for assessing gut barrier effects. Adhesion has been related to shortening the duration of di arrhea, immunogenic effects, competitive exclusion, and other health effect s. Adhesion properties should be carefully monitored, including adhesion to intestinal cells (eg, Caco-2) and human intestinal mucus. This article out lines the types of in vitro testing that can be used to ensure quality cont rol of functional probiotic strains.