Proteins are organic polymers made up of chains of amino acids and are crucial material in many biological functions (Reece and others 2011). There are twenty basic amino acids, eight of which are essential to the adult human diet and must be consumed rather than synthesized inside the body. These essential amino acids are isoleucine, leucine, tryptophan, lysine, valine, phenylalanine, methionine, and threonine, with an added requirement of histidine in the diet of children (Potter and Hotchkiss 1995). Nonessential amino acids can be synthesized from these, and all amino acids are used as monomers to construct proteins which perform numerous important functions in the body (Reece and others 2011).
Most amino acids exist as isomers and are given a designation based on whether they rotate a plane of polarized light to the right or to the left, known as dextrorotatory “D” or levorotatory “L” isomers, respectively (Al-Holy and Rasco 2007). It should be noted that only L amino acids are used in protein synthesis (Weber and Miller 1981).
The biological functions of proteins include increasing the rate of biochemical reactions in the form of enzymes, moving important substances to where they are needed in the form of transport proteins, regulating the body in the form of hormones, allowing the body to move in the form of contractile proteins, and providing support in the form of structural proteins (Reece and others 2011).
In addition, proteins have a great deal of functionality in foods, including providing essential amino acids as well as energy, viscosity, texture, water holding capacity, foaming and emulsification properties, and allowing gel formation (Culbertson 2007). As mentioned above, essential amino acids provided by the diet and nonessential amino acids synthesized in the body are crucial parts of every person’s biochemistry. Protein is also an energy-yielding nutrient and supplies about 4 kilocalories per gram of protein (Potter and Hotchkiss 1995). Not every function of proteins in food is a positive one; proteins in food also can cause an allergic reaction in some individuals and can act as toxins when produced by certain microorganisms (Al-Holy and Rasco 2007).
Protein isolates are highly refined versions of specific proteins, often of soy proteins and milk proteins used as a supplement or ingredient (Sorgentini and others 1995). Milk proteins isolated often include casein and whey (Driskell and Wolinsky 2000).
Soy protein isolates are often used for their emulsification properties and to add a pleasing texture to such foods as confections and convenience foods (Siegwein and others 2011). The milk protein whey is yielded as a byproduct of cheese-making and is often used in protein supplements which are touted as miraculous for muscle development, but this category of protein must not be overestimated and is no replacement for adequate nutritional intake in the general population (Ha and Zemel 2003). Casein is most commonly...