Amino acids and proteins, denaturation and coagulation Top: Three of the 20-odd amino acids important in food Each amino acid has a common end including an amino (NH2) group, by which amino acids bond to each other into long chains called proteins, and a variable end or “side group” that can form different kinds of bonds with other amino acids Center: A chain of amino acids shown schematically, with some of the side groups projecting from the chain The amino acid chain can fold back on itself, and some of the side groups form bonds with each other to hold the chain in a folded shape Bottom: Heating and other cooking processes can break the fold-stabilizing bonds and cause the long chains to unfold, or denature (left, center) Eventually the exposed side groups form new bonds between different protein chains, and the proteins coagulate , or form a permanently bonded solid mass (right) Proteins in Water In living systems and in most foods, protein molecules are surrounded by water Because all proteins are capable to some extent of hydrogen bonding, they absorb and hold at least some water, although the amounts vary greatly according to the kinds of side groups present and the overall structure of the molecule Water molecules can be held “inside” the protein, along the backbone, and “outside,” on polar side groups Whether or not a protein is soluble in water depends on the strength of the bonds ... Water molecules can be held “inside” the protein, along the backbone, and “outside,” on polar side groups Whether or not a protein is soluble in water depends on the strength of the bonds ... all proteins are capable to some extent of hydrogen bonding, they absorb and hold at least some water, although the amounts vary greatly according to the kinds of side groups present and the overall structure of the molecule...Heating and other cooking processes can break the fold-stabilizing bonds and cause the long chains to unfold, or denature (left, center) Eventually the exposed side groups form new bonds between