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A whey protein isolate (often whey isolate) is a dietary supplement and food ingredient created by separating components from milk. Whey is a by-product of the cheese-making process. Whey can be processed to yield whey protein in three forms: whey isolate, whey concentrate, or whey hydrolysate. The difference between the whey protein forms is the composition of the product, particularly the protein content. Whey isolates contain the higher percentage of pure protein and can be pure enough to be virtually lactose free, carbohydrate free, fat free, and cholesterol free.
Whey proteins are highly bioavailable, are very quickly absorbed into the body, and have a high concentration of branched-chain amino acids (BCAAs)  which are highly concentrated in muscle tissue, and are used to fuel working muscles and stimulate protein synthesis.
Whey isolates have had their base component (water) removed and are generally considered almost lactose and cholesterol free — they are at least 90% protein by weight.
Two separation methods are widely used. One method, utilizes ion exchangers which extract native whey protein from the whey stream according to the surface charge characteristics of the molecule, also known as the zeta-potential. This method uses mild pH adjustments to activate and subsequently deactivate the attraction between the ion exchange resin and the protein molecules. In between the temporary binding of protein to the resin, non-protein components are thoroughly washed from the reactor. This process may or may not damage the proteins, but no scientific evidence exists to suggest that it does. Although strong acids and bases are used for the adjustment, the pH rise itself is quite small and within the range common in foods. Changes in protein conformation within this range are reversible and are not considered denaturation. Ion exchange is highly specific to native whey proteins and is generally more selective in what is retained during the process. This is why the process is best known for creating highly pure whey proteins.
The second method, membrane filtration, typically a combination of microfiltration and ultrafiltration, uses molecular size as the basis for separating components from the whey stream. In the process, pressure is applied across a membrane surface which forces smaller molecules through the membrane while larger molecules are retained. Both methods yield a very high protein to non-protein product ratio, although membrane filtration is somewhat less selective allowing any molecule within a size range to be retained. One compositional difference between whey protein isolates made from cheese whey via membrane filtration compared to ion exchange is that membrane filtration includes significant levels of the casein fragment caseino-glycomacropeptide (cGMP). This fragment has a less complete amino acid profile and is low in branched chain amino acids.
As a dietary supplement, whey and other protein powders can be reconstituted at the time of usage by the addition of a solvent such as water, juice, milk, or other liquid. As a food ingredient, whey powders are easily mixed or dissolved into a formulated food.
Whey protein is popular among athletes today because of its ability to be digested very rapidly and help return the post-workout body back from a catabolic (muscle-wasting) state to an anabolic (muscle-building) state. Because of their filtration methods, whey isolates tend to be less allergenic than concentrates and other bovine milk or dairy products. Whey protein isolates are also widely used in infant formula to provide a natural source of amino acids for optimal growth and development, as well as for protein fortification of bars, beverages, dairy products, extruded snacks and cereals and other food products.
Dehydrated (powdered) concentrates and isolates have reduced packaging and shipping requirements, and extended shelf lives. They are readily available.
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