ACE-inhibitory peptides from bovine caseins released with peptidases from Maclura pomifera latex

Abstract

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.