How proteins are digested to liberate amino acids

Digestion is obtained by actions of stomach acid (low pH) and enzymes both in the stomach & intestines (pancreatic protease). In the acidic environment of the stomach, the negatively charged side chains are removed by pepsin. In the more alkaline environment of the intestine, the positively charged side chains are removed by trypsin. In the stomach, Pepsin helps to "unwind" the proteins and breaks the bonds between the amino acids in certain places. In the small intestine other enzymes break the bonds between different amino acids than pepsin does. Because proteins are such complicated molecules it takes a long time and more than one enzyme to completely break them down into amino acids. Digestion results in about 60% small peptides (or peptide bound), which are longer chains of amino acids, and 40% free amino acids (free form). Peptides can be further broken down by hydrolysis in enterocytes (intestinal absorptive cells, simple columnar epithelial cells found in the small intestines and colon).

All proteins are naturally hydrolyzed by stomach acid during normal digestion and the amounts in mineral chelates are in milligram, not gram, strengths. Fermentation to make healthy foods like cheese, vinegar, yogurt, miso, etc. also digests proteins and liberates amino acids, which are of course essential to human nutrition.

Although the excitatory amino acids aspartic acid and glutamic acid are not essential amino acids, the body can create them from numerous sources. In fact, glutamine is the major circulating amino acid and the brain will break down muscles to get it for fuel if the blood sugar is too low to support brain function. Glutamine also fuels some intestinal cells.