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Effect of Heat on a Protein-rich Diet |
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Protein is vital for growth, repair and maintenance of the body. Protein can also be used to provide the body with energy, once it has been used for its main function of growth and repair. Our bodies are composed of millions of cells which are constantly being replaced and repaired. As the body grows, new cells are added. Each cell contains a substance called protoplasm, which mainly contains proteins.
Meat, milk, cheese, egg white, egg yolk, wheat, maize, barley and fish are all healthy sources of protein.
When proteins are heated, their chemical structure is denatured. Remember, this is permanent alternation and can not be reversed. As heating continues, proteins coagulate and generally become less soluble. If overheated, they become less digestible. The effect of heat on specific proteins is discussing below.
Meat: Molecules of connective protein start to coagulate at 60 degrees C, contracting as they do so, and causing the meat to shrink. Under 100 degrees C, coagulation is slow; over 100o C coagulation is rapid and the protein becomes hard and less digestible. In the presence of moisture, collagen is converted into the protein gelatin, which is soluble.
Milk: lactalbumin and lactoglobulin (proteins in milk) coagulate gradually as milk is heated and form a 'skin' on the surface.
Wheat: gluten (protein in cereals) starts to coagulate at 80 degrees C and continues to do so until the heating ends. In this way, it helps to form the structure of cakes, bread and other baked wheat products.
Egg white: At 60 degrees C coagulation starts when ovalbumin denatures into a solid, and continues until the whole white is solid and opaque.
Egg yolk: Protein starts to denature at 70 degrees C, and continues to do so until the yolk becomes dry and hard.
Cheese: Protein coagulates rapidly to a rubbery texture and finally to a crisp and less digestible state.
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