What is the role of the bcaa and glutamine present in whey protein ? what is the special about whey protein ?why dont we replace the whey by n food?

Muscle recovery: Glutamine and BCAAs in whey protein are peptide-bonded amino acids. When ingested, these need to be broken down by digestive enzymes to release these amino acids, therefore take more time before they can appear in the bloodstream. Glutamine and BCAA supplements contain AA in the free form. The body does not need to break down any protein to obtain these amino acids (rapidly available).

Amino acids: Branched chain amino acids are essential AA and are added to whey products to make the whey product more complete. Same for glutamine. Glutamine also is a known promoter of immune health in GI tissue and it high doses on an empty stomach, can stimulate growth hormone release a bit. So, the producers are aiming to amplify "value" of their product. Whey is naturally derived - so is healthy itself.