The body can manufacture most of the amino acids it needs from carbohydrate, fat, and other amino acids. These are called nonessential amino acids. This is a somewhat inaccurate term, since the nonessential amino acids are essential for life. They are nonessential only in the sense they do not have to be obtained from the diet.
Eleven other amino acids cannot be manufactured in amounts needed to support growth and maintenance. These are the essential amino acids, and they must be obtained from the diet. Without them, protein cannot be made and body tissues cannot be maintained.
Hydrolysis (breakage of a peptide bond) (two amino acid proteins), and tripeptides (three amino acid proteins), which are easily absorbed by the digestive tract. (Conversely, a peptide bond is formed by removing a molecule of water from two adjacent amino acids.)
The peptide bond can be easily attacked by the digestive enzymes of bacteria. The bacterial growth and formation of potentially toxic proteins as a by product are the cause of food spoilage. This is why protein foods such as milk, eggs, meat, poultry, and fish must be refrigerated.