Whey protein concentrate is the least processed form of whey protein and is 35%–80% protein by weight, although most whey protein concentrate powders tend to be standardized at 80% protein by weight.[1]
Whey protein isolate is defined as being more than 90% protein by weight.
Whey hydrolysate is protein that has been pretreated with enzymes and acid to reduce its peptide size; it’s the fastest absorbed form of whey. Hydrolysis reduces the allergic potential of whey and milk protein by breaking down immunogenic, larger peptides into smaller ones less-apt to be recognized by the immune system. This why hydrolyzed whey is often used in infant formula. Hydrolyzed whey also tends to have increased solubility compared to whey isolate, although it is important to note that whey protein in general (including whey isolate) is quite soluble. Several studies comparing whey hydroylsate to whey isolate and other milk proteins such as casein failed to make a difference in nutritional quality.[2]
Is one form better than the others? Not necessarily, but this can vary by the individual. Since whey hyrolysates are inherently less immunogenic, they are useful for people who can't tolerate whey concentrate or isolate. As far as efficacy in-general, including their ability to faciliate muscle hypertrophy or recovery, there haven’t been many comparison studies. One trial noted that whey hydrolysate may enhance muscle recovery more than whey isolate.[3] Whether or not the differences observed in this trial would be experienced outside of a controlled laboratory setting is unclear.