Whey protein concentrate (WPC) was subjected to enzymatic hydrolysis by proteases from the flowers of Cynara cardunculus, and the resulting angiotensin-converting enzyme (ACE)-inhibitory effect was monitored. The whole WPC hydrolysate exhibited an IC50 value of 52.9 +/- 2.9 mu g/mL, whereas the associated peptide fraction with molecular weight below 3 kDa scored 23.6 +/- 1.1 mu g/mL The latter fraction was submitted to RP-HPLC, and 6 fractions were resolved that exhibited ACE-inhibitory effects. Among the various peptides found, a total of 14 were identified via sequencing with an ion-trap mass spectrometer. Eleven of these peptides were synthesized de novo - to validate their ACE-inhibitory effect, and also to ascertain their stability when exposed to simulated gastrointestinal digestion. Among them, three novel, highly potent peptides were found, corresponding to alpha-lactalbumin f(16-26) - with the sequence KGYGGVSLPEW, alpha-lactalbumin f(97-104) with DKVGINYW, and beta-lactoglobulin f(33-42) with DAQSAPLRVY; their IC50 values were as low as 0.80 +/- 0.1, 25.2 +/- 1.0 and 13.0 +/- 1.0 mu g/mL, respectively. None of them remained stable in the presence of gastrointestinal enzymes: they were partially, or even totally hydrolyzed to smaller peptides - yet the observed ACE-inhibitory effects were not severely affected for two of those peptides.