Proteins are amazing chemical polymers. They perform a myriad of functions such as providing nutrition in the form of constituent amino acids and energy. They serve as reagents and enzymes in chemical reactions. Proteins contribute to the texture, viscosity, and water-holding capacity of foods that contain them. Proteins can be toxins, allergens or hormones and act as carriers for vital molecules such as oxygen in the bloodstream (Coultate 1984). These polymers have evolved to play a role in very specific physiological functions, and this chemical reactivity can be used for truly unique applications that go beyond the evolutionary scope of proteins. The chemical and physical nature of a protein such as its isoelectric point, solubility and size, and its biological attraction to other molecules can all be exploited to separate a particular protein from the solution in which it resides. Typically several steps are used to purify a particular protein. These include heating, acidification, subjecting a solution to reducing conditions, and drying. More sophisticated techniques include chromatography, ultrafiltration, reverse osmosis, and high-pressure liquid chromatography (Kinsella and Whitehead 2001). The isolation of proteins from their original matrices allows their use in different food systems to improve qualities such as nutritional value, texture and stability. For a protein to perform these latter functions, it must have certain characteristics such as solubility, gelation, ligand binding or film-forming properties. Today, non-native proteins are widely used to improve food quality. Products include ice cream, beverages, cereals, baked goods, snack foods, and dairy products...... middle of paper...... 1979. Functional properties of soy proteins. Journal America Oil Chemists' Society 56:242-258.Kinsella JE and Whitehead. 1989. Whey proteins: chemical, physical and functional properties. Advances in Food and Nutrition Research 33:343-439.McMahon DJ and Brown RJ. 1984. Composition, structure and integrity of casein micelles: a review. Journal of Dairy Science 67:499-512.Mendel F and Brandon DL. 2001. Nutritional and Health Benefits of Soy Protein. Journal of Agricultural and Food Chemistry 49(3):1069-1086.Southward CR. Casein-based products. New Zealand Dairy Research Institute.Thompson LD., Dinh T. 2009. FDSC 4303/5305 Food Chemistry Laboratory Manual. Lubbock, TX: Texas Tech University, Department of Animal and Food Sciences. Walstra P. 1990. On the stability of casein micelles. Journal of Dairy Science 73:1965-1979.