Whey protein is commonly marketed and ingested as a dietary supplement, and various health claims have been attributed to it in the alternative medicine community. Although whey proteins are responsible for some milk allergies, the major allergens in milk are the caseins.
Whey is left over when milk is coagulated during the process of cheese production, and contains everything that is soluble from milk after the pH is dropped to 4.6 during the coagulation process. It is a 5% solution of lactose in water, with some minerals and lactalbumin. The fat is removed and then processed for human foods. Processing can be done by simple drying, or the protein content can be increased by removing lipids and other non-protein materials. For example, spray drying after membrane filtration separates the proteins from whey.
Whey can be denatured by heat. High heat (such as the sustained high temperatures above 72 °C associated with the pasteurization process) denatures whey proteins. While native whey protein does not aggregate upon renneting or acidification of milk, denaturing the whey protein triggers hydrophobic interactions with other proteins, and the formation of a protein gel. Heat-denatured whey can still cause allergies in some people.
Whey protein is the collection of globular proteins isolated from whey. The protein in cow's milk is 20% whey protein and 80% casein protein, whereas the protein in human milk is 60% whey and 40% casein. The protein fraction in whey constitutes approximately 10% of the total dry solids in whey. This protein is typically a mixture of beta-lactoglobulin (~65%), alpha-lactalbumin (~25%), bovine serum albumin (~8%)(see also serum albumin), and immunoglobulins. These are soluble in their native forms, independent of pH.
Being a by-product of the cheese making process, and likelihood of animal rennet use, whey protein as well as casein products may not be suitable for consumption by lacto-vegetarians or observers of kosher dietary laws. There are, however, specialty producers of vegetarian-approved whey protein products produced using non-animal "rennet" (enzymes). These products are often also labeled as kosher and halal approved.
The amino acid cysteine in whey protein is a substrate for the synthesis of glutathione in the body which is an ubiquitous cellular antioxidant; laboratory experiments have suggested that whey protein and its components might reduce the risk of cancer in animals, suggesting an avenue for future medical research.
- Concentrates have typically a low (but still significant) level of fat and cholesterol but, in general, compared to the other forms of whey protein, have higher levels of bioactive compounds, and carbohydrates in the form of lactose — they are 29%–89% protein by weight.
- Isolates are processed to remove the fat, and lactose, but are usually lower in bioactivated compounds as well — they are 90%+ protein by weight. Like whey protein concentrates, whey protein isolates are mild to slightly milky in taste.
- Hydrolysates are whey proteins that are predigested and partially hydrolyzed for the purpose of easier metabolizing, but their cost is generally higher. Highly hydrolysed whey may be less allergenic than other forms of whey.
- Native whey protein, the purest form of whey protein which has been extracted from skim milk and not a by product of cheese production, produced as a concentrate and isolate.
The use of whey protein as a source of amino acids and its effect on reducing the risks of diseases such as heart disease, cancer and diabetes has been the focus of ongoing research as of 2007[update]. Whey is an abundant source of branched-chain amino acids (BCAAs), which are used to stimulate protein synthesis. When leucine is ingested in high amounts, such as with whey protein supplementation, there is greater stimulation of protein synthesis, which may speed recovery and adaptation to stress (exercise). Whey has approximately three grams of leucine per serving and the threshold for optimal protein synthesis is three grams.
Scientific evidence has shown that proteins high in essential amino acids (EAA), branched chain amino acids (BCAA), and particularly leucine (Leu) are associated with increased muscle protein synthesis, weight loss, body fat loss, and decreased plasma insulin and triglyceride profile. A study done by Hulmi et al. (2009) had subjects either consume a whey protein drink or placebo, the results showed that the whey protein sample had a three percent increase in the cross section area of the vastus lateralis muscle and a five percent increase in the muscle force of the isometric leg extension. However, there was no convincing evidence that comparative upper body muscle mass or strength was increased nor was there any significant increase in quadriceps femoris other than the vastus lateralis.
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"The change of the average QF CSA was higher in the protein group (9.9 ± 7.4%)compared to placebo (7.5 ± 4.8%) but the difference did not reach statistical significance (P0.05)....The average increase in the VL muscle (VL1–4) was significantly higher in the protein group (relative increase: 14.8 ± 6.8%) compared to the placebo (11.2 ± 5.6%) (P\0.05)....However, compared to the control group (8.0 ± 9.5%, P[0.05), isometric leg extension increased significantly only in the protein group (a relative increase of 24.3 ± 12.3%, difference between the groups P = 0.02), whereas the increase was not significant in the placebo group (19.3 ± 15.5%, P = 0.23).
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