Gastric acid 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. The highly acidic environment in the stomach lumen causes proteins from food to lose their characteristic folded structure (or denature). This exposes the protein's peptide bonds. The gastric chief cells of the stomach secrete
Tannic acid many parts of the world, such uses are permitted. In the United States, tannic acid is generally recognized as safe by the Food and Drug Administration. According to EU directive 89/107/EEC tannic acid cannot be considered as a food additive and consequently does not hold an E number. Under directive 89/107/EEC tannic acid can be referred to as a food ingredient. The E-number E181 is sometimes incorrectly used to refer to tannic acid; this in fact refers to the INS number assigned to tannic acid under the FAO-WHO Codex Alimentarius system. Tannins are a common impurity in the beverage ayahuasca