Production of angiotensin-I-converting-enzyme-inhibitory peptides in fermented milks started by Lactobacillus delbrueckii subsp bulgaricus SS1 and Lactococcus lactis subsp cremoris FT4

Two fermented milks containing angiotensin-I-converting-enzyme (ACE)-inhibi tory peptides were produced by using selected Lactobacillus delbrueckii sub sp. bulgaricus SS1 and L. lactis subsp, cremoris FT4. The pH 4.6-soluble ni trogen fraction of the two fermented milks was fractionated by reversed-pha se fast-protein liquid chromatography. The fractions which showed the highe st ACE-inhibitory indexes were further purified, and the related peptides w ere sequenced by tandem fast atom bombardment-mass spectrometry. The most i nhibitors fractions of the milk fermented by L, delbrueckii subsp, bulgaric us SS1 contained the sequences of p-casein (P-CN) fragment 6-14 (f6-14), f7 -14, f73-82, f71-82, and f75-82. Those from the milk fermented by L. lactis subsp, cremoris FT4 contained the sequences of P-CN f7-14, f47-52, and f16 9-175 and kappa-CN f155-160 and f152-160. Most of these sequences had featu res in common with other,ACE-inhibitory peptides reported in the literature . In particular, the beta-CN f47-52 sequence had high homology with that of angiotensin-II. Some of these peptides were chemically synthesized, The 50 % inhibitory concentrations (IC(50)s) of the crude purified fractions conta ining the peptide mixture were very low (8.0 to 11.2 mg/liter). When the sy nthesized peptides were used individually, the ACE-inhibitory activity was confirmed but the IC(50)s increased considerably. A strengthened inhibitory effect of the peptide mixtures with respect to the activity of individual peptides was presumed. Once generated, the inhibitory peptides were resista nt to further proteolysis either during dairy processing or by trypsin and chymotrypsin.