between molecules, and on whether water can separate the molecules from each other by hydrogen bonding The wheat proteins that form gluten when flour is mixed with water are a kind of protein that absorbs considerable amounts of water but doesn’t dissolve, because many fat-like groups along their molecules bond with each other, hold the proteins together, and exclude water Similarly, the proteins that make up the contracting muscle fibers in meat are held together by ionic and other bonds On the other hand, many of the proteins in milk and eggs are quite soluble Protein Denaturation A very important characteristic of proteins is their susceptibility to denaturation, or the undoing of their natural structure by chemical or physical means This change involves breaking the bonds that maintain the molecule’s folded shape (The strong backbone bonds are broken only in extreme conditions or with the help of enzymes.) Denaturation is not a change in composition, only a change in structure But structure determines behavior, and denatured proteins behave very differently from their originals Proteins can be denatured in many ways: by exposing them to heat — usually to somewhere between 140–180ºF/60–80ºC — or to high acidity, or to air bubbles, or to a combination of these In each case, the unusual chemical or physical conditions — increased molecular agitation, or lots of reactive protons, or the drastic difference between the air bubble and the liquid wall that surrounds it — breaks many of the bonds between amino acid side groups that hold the protein molecule in its specific folded shape The long proteins therefore unfold, exposing many more of their reactive side groups to the watery environment ...molecule’s folded shape (The strong backbone bonds are broken only in extreme conditions or with the help of enzymes.) Denaturation is not a change in composition, only a change in structure... combination of these In each case, the unusual chemical or physical conditions — increased molecular agitation, or lots of reactive protons, or the drastic difference between the air bubble and the liquid wall that... surrounds it — breaks many of the bonds between amino acid side groups that hold the protein molecule in its specific folded shape The long proteins therefore unfold, exposing many more of their reactive side groups to the