Gastric digestion of proteins

In the stomach, pepsin and related enzymes initiate the enzymatic digestion of proteins, which takes 1-3 hours. The acidic gastric contents are then released into the duodenum in batches, where they are neutralized by alkaline pancreatic secretions and mixed with cystic bile. 

As the acidic stomach contents pass into the small intestine, the low pH triggers secretion of the hormone secretin into the blood. Secretin stimulates the pancreas to secrete bicarbonate into the small intestine to neutralize the gastric HC1, abruptly increasing the pH to about 7. (All pancreatic secretions pass into the small intestine through the pancreatic duct.) The digestion of proteins now continues in the small intestine. Arrival of amino acids in the upper part of the intestine (duodenum) causes release into the blood of the hormone... 

The digestion of proteins begins in the stomach, which secretes gastric juice—a unique solution containing hydrochloric acid and the proenzyme, pepsinogen ... 

Yvon, M., Beucher, S., Scanff, P.,Thirouin, S., and Pelissier, J. P. (1992), In vitro simulation of gastric digestion of milk proteins Comparison between in vitro and in vivo data, J. Agric. Food Chem., 40, 239-244. 

The gastric phase of protein digestion is not absolutely required for health. Patients lacking gastric function because of a gastrectomy (surgical removal of the... 

The digestion of proteins involves the salivary glands, the gastric mucosa, and the pancreas, all which introduce digestive enzymes into the gastrointestinal tract (Chaney, in Devlin, 1986, p. 11350). These actions are assisted by hydrochloric acid secreted in the gastrointestinal tract, and by the presence of sodium chloride and sodium bicarbonate. 

As previonsly indicated, the digestion of proteins is ordinarily considered to occur successively via the gastric, pancreatic, and intestinal stages, as per the respective sources of the digestive enzymes. Gastric juices include proteases of the pepsin family, as well as hydrochloric acid. Pancreatic juice contains a number of protease enzymes snch as trypsin, chymotrypsin, and elastase, and some are noted to involve a serine residne, serine being 1 of the 20 amino acids incorporated into protein molecules. Hence, the term sometimes nsed is serine protease. 

London found only traces of amino acids in gastric contents during digestion of protein, and he enlisted the cooperation of Emil Abderhalden to determine whether amino acids are produced but disappear because they are absorbed. London mixed amino acids with meat that had been extracted with water to remove any trace of amino acids, and he gave the gastric effluent to Abderhalden for analysis. Abderhalden, using methods already described, did the appropriate control... 

Fu, T.J., Abbott, U. And Hatzos, C., Digestibility of food allergens and non-allergenic proteins in simulated gastric and intestinal fluids — a comparative study. J. Agric. Food Chem., 50, 7154, 2002. 

Much of the early work which would lead to the identification of proteins as defined chemical entities started from observations on enzymes, either those involved in fermentation or on the characterization of components in gastric secretions which powerfully catalyzed the hydrolysis of different foodstuffs. As well as the digestive enzymes, a number of relatively pure proteins could be isolated from natural sources where they made up the major component (Table 1). Because of the importance and difficulty of isolating pure proteins and demonstrating their homogeneity, functionally active and relatively abundant... 

The protein portion of the nucleoproteins is basic in nature and being complex in structure may form several types of linkage, depending upon the type of nucleic acid. In gastric digestion or hydrolysis with weak acid, nucleoproteins yield protein and nuclein. The latter in pancreatic digestion or hydrolysis with weak alkali yields additional protein and nucleic add. See also Nucleic Acids. 

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