to reach the intestine, strains must first pass through the stomach, which secretes hydrochloric acid and enzyme. More than two litres of gastric juice is secreted each day, with a pH as low as 1.5 providing a barrier to the entrance into the gut of bacteria .
The survival of potential probiotic strains to gastric juice depends on their intrinsic resistance to the hostile environment but also on the host and the ingestion vector. Foods with a high level of fat and the presence of certain proteins in the food may protect the bacteria from stomach acid and thus increase survival to gastric transit.A mechanism proposed for the beneficial effect of foods and food ingredients is the increase in the pH of gastric contents resulting from the addition of food.