The effects of heat-induced denaturation of whey protein isolate (WPI) on the enzymatic breakdown of alpha-La, caseinomacropeptide (CMP), beta-Lg A and beta-Lg B were observed as hydrolysis proceeded to a 5% degree of hydrolysis (DH) in both unheated and heat-treated (80 degrees C, 10 min) WPI dispersions (100 g L-1). Hydrolysis of denatured WPI favoured the generation of higher levels of free essential amino acids; lysine, phenylalanine and arginine compared to the unheated substrate. LC-MS/MS identified 23 distinct peptides which were identified in the denatured WPI hydrolysate - the majority of which were derived from beta-Lg. The mapping of the detected regions in alpha-La, beta-Lg, and CMP enabled specific cleavage points to be associated with certain serine endo-protease activities. The outcomes of the study emphasise how a combined approach of substrate heat pre-treatment and enzymology may be used to influence proteolysis with attendant opportunities for targeting unique peptide production and amino acid release. (C) 2013 Published by Elsevier Ltd.