In work reported here, a proteolytic extract prepared from Maclura pomifera latex was employed to hydrolyze bovine caseins. Densitograms of Tricine-sodium-dodecyl-sulfate-polyacrylamide-gel electrophoresis (SDS-PAGE) indicated that the caseins were considerably degraded after a 10-min reaction. The degree of hydrolysis determined by the 2,4,6-trinitrobenzenesulfonic-acid method was 17.1 +/- 0.7% after 180 min of digestion. The concentration of small peptides increased with hydrolysis time, and analysis by reverse-phase high-performance liquid chromatography (RP HPLC) and mass spectrometry, revealed a virtually unchanged peptide profile. These results suggested that those proteases were highly specific, as only certain peptide bonds were cleaved. The hydrolysate of 180 min displayed the highest inhibition of angiotensin-converting enzyme (ACE) showing an IC50 of 1.72 +/- 0.25 mg/mL, and the analysis of the peptide fractionation in this hydrolysate by RP HPLC exhibited two peaks responsible for that activity. Fragmentation analysis through the use of iterated matrix-assisted-laser-desorption-ionization-time-of-flight mass spectrometry (MALDI-TOF/TOF MS/MS) with the aid of bioinformatics tools enabled us to deduce two peptide sequences one, YQEPVLGPVRGPFPIIV, having been previously reported as an ACE-inhibitor; the other, RFFVAPFPE, as yet undescribed. The presence of bioactive peptides in these casein hydrolysates argues for their potential use in the development of functional foods. (C) 2017 Elsevier Ltd. All rights reserved.