Proteins are amazing chemical polymers. They serve a myriad of functions such as providing nutrition in the form of their constitutive amino acids as well as energy. They serve as reactants and enzymes in chemical reactions. Proteins contribute to the texture, viscosity and water holding capacity of foods that contain them. Proteins can be toxins or allergens or hormones, and they serve as transporters for vital molecules such as oxygen in the blood stream (Coultate 1984). These polymers have evolved to play a role in very specific physiological functions and this chemical reactivity can be used for very unique applications beyond a proteins evolutionary scope.
A protein’s chemical and physical nature such as the isoelectric point, solubility and size, and its biological attraction to other molecules all can be exploited to separate a particular protein from the solution in which is 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, ultra filtration, reverse osmosis, and high-pressure liquid chromatography (Kinsella and Whitehead 2001).
The isolation of proteins from their original matrices allows for their use in different food systems to improve such qualities as nutritional value, texture, and stability. In order for a protein to serve in the latter capacities it must have certain characteristics such as solubility, gelation, ligand-binding or film formation properties. Today there is extensive use of non-native proteins to improve food quality. Products include ice creams, beverages, cereals, baked goods, snack items and dairy items (KInsella 1979).
Soy proteins are used for both their nutritional and functional properties. These proteins are a result of the activity of nitrogen-fixing bacteria and soybean seed contains up to 48% protein (Kinsella 1979). They are used in infant formulas, flour, protein isolates, cheeses, drinks, tofu and salami. Infant formulas made from soy proteins serve as an excellent alternative in cases where milk allergies prevent the use of other types of formula. These proteins are deficient in methionine, one of the essential amino acids required by man, and the content of lysine is lower than that of casein, a protein found in milk. In addition to nutritional value, studies have shown that soy protein may play a positive role in several human health concerns such as lowering cholesterol, they have anticarcinogenic effects, and they may help control conditions such as diabetes, digestive tract irritation, and bone and kidney disease (Mendel and Brandon 2001).
Soy proteins in addition to beneficial properties also contain inhibitors for digestive enzymes that prevent the complete utilization of the protein after consumption. The nutritional quality of any substance is gauged not only by its content of amino acids...