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Abstract:The angiotensin-I converting enzyme (ACE) inhibitory activity of the milk fermented with Lactococcus lactis subsp. lactis NBRC 12007 and Saccharomyces cerevisiae K7 in monoculture and co-culture was evaluated. Bovine full-fat milk was fermented with each strain in monoculture and co-culture at 30 ºC for 72 h, and the in vitro ACE inhibitory activity (%) of each milk sample was determined by a fluorogenic assay using H-(2)Abz-Acp(6)-Ala-Phe(4-NO 2 )-Leu-OH as the substrate. The ACE inhibitory percentages of the milk samples fermented with L. lactis subsp. lactis NBRC 12007 and S. cerevisiae K7 monocultures and the co-culture was 33, 27 and 25 %, respectively, which varied significantly (p < 0.05). Each milk sample was fractionated by semi-preparative HPLC analysis and the ACE inhibitory activity (%) of each fraction was determined using the same substrate, which varied from 20 -47 %, 16 -37 % and 16 -31 % in the milk fermented with L. lactis subsp. lactis NBRC 12007, S. cerevisiae K7 and the co-culture, respectively. The highest ACE-inhibitory activity (47 %) was observed in fraction-2 of the milk fermented with L. lactis subsp. lactis NBRC 12007. The results concluded that the two strains tested were able to hydrolyze milk proteins into ACE-inhibitory peptides in order to produce fermented milk products with ACE-inhibitory activity, both in monoculture and co-culture. Therefore, it can be suggested that these strains can be successfully utilized in the dairy industry in manufacturing fermented milk products with ACE-inhibitory activity as a dietary supplement and/or as an alternative approach for antihypertensive medication.