Gastric juice is a mixture of hydrochloric acid, pepsin and rennin enzymes and is synthesized and secreted from gastric (oxyntic) glands situated in the wall of the stomach. Gastric juice is highly acidic with a pH value of pure secretion being 1.0 due to a very high concentration of hydrochloric acid. After mixing with food, the pH of gastric contents becomes approximately 2.5 which is suitable for the digestion of proteins in the stomach. Rennin enzyme causes curdling of milk by converting casein (milk protein) into calcium paracaseinate.