Whey is one of two major sources of protein found in milk (the other is casein.) When cheese is manufactured from milk the curd (casein) is used and the whey is separated out. At this point, whey is about 92% water, 6.5% lactose, 0.9% protein and 0.2% vitamins, minerals and fat-soluble nutrients. It is refined to produce whey protein concentrates (WPC), whey protein isolates (WPI), and hydrolyzed whey peptides (HWP).
WPC was the first commercially produced whey protein product.
When used to produce WPC, crude whey goes through an ultrafiltration process, which decreases it to just 20% of its original volume. The concentrated whey liquid is then diafiltered at low temperatures to remove large quantities of fat, lactose, and cholesterol. The resulting solution is then carefully dried to create a powder yielding between 34% and 89% protein by dry weight.
This finished product, commonly known as whey protein concentrate, is the major protein contributor in many commercial whey protein supplements. In addition to being an excellent source of amino acids, WPC is easily digested, relatively inexpensive, and quite palatable.
Ion-Exchanged Protein Isolates are separated through an electrical charge. Though not as "native" (maintaining the same microfraction ratios found in milk) as cross-flow microfiltered whey protein isolates, ion-exchange WPI's are richer in total protein - containing upwards of 97-98% by dry weight - more than any other type of whey protein.
Cross-flow microfiltration (CMF) is a solvent-free process that uses natural ceramic filters to isolate whey proteins from a variety of undesirables (i.e. fat, cholesterol, lactose, etc.). CFM is better at preserving the protein microfractions, with minimal denaturation and is generally higher in calcium and lower in sodium content than ion-exchange isolates. CFM WPI's are more expensive and yield higher protein levels than concentrates.
Whey Protein Isolate is the best form of protein for a post-workout nutrition. That critical time after severe physical stress when the cells will act like a sponge and take in almost anything. The extreme hunger of the cells and the fast-acting properties of whey isolate will make sure you use the best window for recovery to the fullest. If not, the body will hunt the stored reserves of nutrients and when on a diet for example that will cause them to rob other muscle-tissue of glutamine.
Hydrolyzed whey peptides (HWP), another type of whey protein material, are commonly recognized as the most bioavailable (useable by the body) and thus a very desirable form of whey protein. HWP's are whey protein concentrates or isolates that have had their peptide bonds strategically predigested (broken) with enzymes or other catalysts. Current scientific evidence suggests that the body absorbs protein in short peptide form even more efficiently than in free form amino acids.
As you probably have guessed, there must be some drawbacks to hydrolyzed whey proteins, otherwise everyone would be using them exclusively to make their products. The first major drawback is taste. HWP's are extremely bitter. Even the most diehard athlete would have a very difficult time downing a tall glass of short chain (low molecular weight) hydrolyzed whey peptides.
Another downside to peptides is depletion of certain microfractions. As the word "hydrolyzed" implies, protein chains have been broken down.
While this will not change the amino acid profile and may actually increase the digestibility/absorbability of the product, it decreases the prevalence of some of the larger microfractions naturally present in crude whey, WPC, and WPI. A final reason HWP's are not used exclusively (or at all) in certain whey protein formulas is cost. Since HWP's start off as WPC's or WPI's, an additional processing step is needed to selectively break the peptide bonds in these larger protein classes.