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Chapter V Discussion
al., 2003). Instead of evaluating the effect of each component in separate experiments, it
would be important to evaluate all components (enzymes, low pH, bile salts, duodenum
secrete and food vehicle) in one system, as the two successive stresses of stomach transit and
small intestinal transit might interact and thereby affect the survival of these strains in a
synergistic way. Therefore, for the viability of bacteria under in vitro gastrointestinal model
of the stomach, it is necessary not only to test the tolerance at low pH, but also the action of
enzymes like pepsin and lysozyme. It is also important to consider the food vehicle in which
the probiotic would be included, as it might exert a protective role and enhance the viability
of bacteria. For this reason, not only the effect of pH, but also that of pepsin and lysozyme
must be included in the stomach passage model. After 1 h incubation under simulated gastric
conditions, a further treatment was followed with simulated intestinal fluids containing bile
salts and pancreatin, which was a pool of pancreatic enzymes (amylases, trypsin, lipase,
ribonuclease and proteases). In this way, both gastric and intestinal stresses were successfully
combined in a simulated in vitro gastrointestinal model.
Using this in vitro simulated stomach-duodenum passage, only 96 strains were able to
survive under the conditions of this study. The fact that only 6 strains out of 96 isolates tested
survived the passage through this model validates the model, since gastrointestinal conditions
are considered to be detrimental to most of food-associated lactic acid bacteria, but the
probiotic control strain which indicated survival under the conditions tested. Highest rate of
survival to the gastrointestinal conditions was observed for L. casei LAM-1. The present
study was based on a ‘worst case’ scenario to determine the most resistant strains as the
conditions selected in the in vitro model were even harsher than that of the real situation,
where the gastric pH after a meal was of approx. 3, and there was a continual removal of the
bile salts, leading to fluctuating and often lower bile levels. As already pointed out by various