Gastric acid
The main constituent of gastric acid is hydrochloric acid which is produced by parietal cells (also called oxyntic cells) in the gastric glands in the stomach. Its secretion is a complex and relatively energetically expensive process. Parietal cells contain an extensive secretory network (called canaliculi) from which the hydrochloric acid is secreted into the lumen of the stomach. The pH of gastric acid is 1.5 to 3.5 in the human stomach lumen, the acidity being maintained by the proton pump H/K ATPase. The parietal cell releases bicarbonate into the bloodstream in the process, which causes a temporary rise of pH in the blood, known as an alkaline tide.
Lactobacillus fermentum
Testing of "Lactobacillus fermentum " against different pH concentration solutions revealed that it has a strong pH tolerance by its ability to grow and survive a few hours after being incubated in a 3-pH level solution. Strains of "Lactobacillus fermentum" have also been tested in different bile concentrations and demonstrated to have good bile tolerance when incubated with 3 g L-1 of bile salt. The pH and bile tolerance that " L. fermentum " demonstrates is significant in terms of its consideration as a probiotic. It has to be strong enough to survive the stresses of the digestive system. The stomach has a pH between 1.5 and 3, and the upper intestine contains 3-5 g L-1 of bile. "Lactobacillus fermentum" has been found to survive in these conditions further supporting the idea that it can act as a probiotic.