Quantification of the angiotensin-converting enzyme-inhibiting tripeptides Val-Pro-Pro and Ile-Pro-Pro in hard, semi-hard and soft cheeses

A new high performance liquid chromatography with subsequent triple mass spectrometry (HPLC-MS3) method for the quantitative determination of Val-Pro-Pro (VPP) and Ile-Pro-Pro (IPP) was applied in a series of 44 traditional cheeses. Additionally, inhibition of the angiotensin-converting enzyme (ACE) was measured in vitro by determination of IC50 values. The correlation coefficients between the IC50 values and the sum of the two peptides VPP and IPP in hard, semi-hard and in the group of soft cheeses were at r=-0.797r=-0.797, −0.580 and −0.357, respectively, suggesting that the high ACE-inhibiting activity found in the water soluble extracts of some investigated hard cheeses was mainly due to the presence of these two tripeptides. Concentrations of VPP and IPP were in the range of 0–224 mg kg−1 and 0–95 mg kg−1, respectively, indicating that some cheese varieties contain similar concentrations of VPP and IPP to recently developed fermented milk products with blood-pressure lowering capacity.