Influence of malt, wheat, and barley extracts on the bile tolerance of selected strains of lactobacilli

Abstract

The bile tolerance of three strains of lactobacilli, selected on the basis of their ability to ferment cereal substrates and tolerate simulated gastric transit was examined. Lactobacillus reuteri (NCIMB 1195), L. acidophilus (NCIMB 8821), and L. plantarum (NCIMB 8826) were exposed to 2% bile for 4 h in a phosphate-saline buffer at pH 7. The effects of supplementing the assays with cereal extracts, increasing concentrations of glucose, and free amino nitrogen was also examined. In the absence of any supplements L. reuteri showed the greatest resistance to bile, whilst L. acidophilus displayed the greatest sensitivity. Addition of cereal extracts improved the tolerance of all three strains, barley and wheat extracts imparted similar levels of enhancement in viability, whilst the addition of malt showed a greater positive influence. The extent of improvement was related to the concentration of soluble sugars and FAN present in the cereals, this was illustrated further by the addition of glucose to the assays, as the viability of the organisms was progressively improved with increasing concentrations. The presence of free amino nitrogen also increased bacterial resistance to bile but to a lesser extent both glucose and cereal extracts.