Angiotensin-converting enzyme-inhibitory peptides in Manchego cheeses manufactured with different starter cultures

The angiotensin-converting enzyme (ACE)-inhibitory activity of water-soluble extracts from Manchego cheeses, which were manufactured with different starter cultures, was monitored during cheese ripening. On activity basis, the 3000 Da permeate from an 8-months-aged cheese, which was prepared with a defined-strain bacterial inoculum, was selected and fractionated by following several chromatographic steps. A total of 22 peptide fragments were identified in nine fractions by electrospray-ionisation-tandem mass spectrometry. Five of them corresponded to αs2-CN-fragments, six to β-CN fragments, and 10 of them were peptides derived from the αs1-CN sequence. The di-peptide, FP, could be originated from hydrolysis of various casein fractions. The complexity of the collected fractions after three chromatographic steps precluded the assignment of a single peptide responsible of the ACE-inhibitory activity. Fragment (199–204) from ovine β-CN, which was included in one of the most active fractions, was chemically synthesised and it was found to have an IC50 value of 592 μm.