No abstract

Fermented milk (FM) with putative antihypertensive effect in humans could be an easy applicable lifestyle intervention against hypertension. The mode of action is supposed to be through active milk peptides, shown to possess in vitro ACE-inhibitory effect. Blood pressure (BP) reductions upto 23 mm Hg have been reported in spontaneously hypertensive rats fed FM. Results from human studies of the antihypertensive effect are inconsistent. However, many studies suffer from methodological weaknesses, as insufficient blinding and the use of office BP measurements. We conducted a randomised, double-blind placebo-controlled study of the antihypertensive effect of Lactobacillus helveticus FM in 94 prehypertensive and borderline hypertensive subjects. The participants were randomised into three treatment groups with a daily intake of 150 ml of FM, 300 ml of FM or placebo (chemically acidified milk). The primary outcome was repeated 24-h ambulatory BP measurements. There were no statistically significant differences in the outcome between the groups (systolic BP (SBP), P ¼ 0.9; diastolic BP (DBP), P ¼ 0.2). However, the group receiving 300 ml FM had reduced BP across the 8-week period in several readings, which could be compatible with a minor antihypertensive effect. Heart rate and lipids remained unchanged between groups. Hence, our study does not support earlier studies measuring office BP-measurements, reporting antihypertensive effect of FM. Based on straight performed 24-h ambulatory BP measurements, milk fermented with Lactobacillus helveticus does not posses significant antihypertensive effect.

No abstract

Despite a known ACE inhibitory effect in vitro and in animals, milk fermented with Lb. helveticus did not inhibit ACE in humans. Our results suggest that the intake of fermented milk decreases sympathetic activity, although not to an extent mediating reductions of blood pressure and heart rate in borderline-hypertensive subjects.

The effect of autoproteolysis of Lactococcus lactis lactocepin III on its specificity towards ␤-casein was investigated. ␤-Casein degradation was performed by using either an autolysin-defective derivative of L. lactis MG1363 carrying the proteinase genes of L. lactis SK11, which was unable to transport oligopeptides, or autoproteolyzed enzyme purified from L. lactis SK11. Comparison of the peptide pools by high-performance liquid chromatography analysis revealed significant differences. To analyze these differences in more detail, the peptides released by the cell-anchored proteinase were identified by on-line coupling of liquid chromatography to mass spectrometry. More than 100 oligopeptides were released from ␤-casein by the cell-anchored proteinase. Analysis of the cleavage sites indicated that the specificity of peptide bond cleavage by the cell-anchored proteinase differed significantly from that of the autoproteolyzed enzyme.Due to their limited capacity for synthesizing amino acids (3), lactococci have to utilize exogenous nitrogen sources for optimal growth. The amino acid requirements appear to be strain specific, but most Lactococcus lactis strains need at least Leu, Ile, Val, and His for growth (15,28). In milk, the concentrations of several essential amino acids, especially those of Ile and Leu (less than 1 mg liter Ϫ1 ), are very low (10, 18). In addition, milk peptides are a poor source of Leu and Met (16). Thus, for optimal growth in milk, lactococci depend on utilization of casein (18,29). A complex proteolytic system is needed for casein hydrolysis. According to proposed models, lactocepin (EC 3.4.21.96; previously named cell envelope proteinase PrtP) (34) is involved in the first step of casein degradation. Only some of the oligopeptides released by lactocepin are taken up by the oligopeptide transport system (Opp) and subsequently cleaved into amino acids by intracellular peptidases (for recent reviews, see references 17 and 22).Two different types of lactocepins (lactocepin I and lactocepin III) have been identified in lactococci on the basis of their specificity for caseins (44). Lactocepin I cleaves ␤-casein preferentially and -casein to a lesser extent. In contrast, lactocepin III cleaves ␤-, -, and ␣ s1 -caseins. There are only 44 differences in the amino acid sequences of lactocepins I and III, and 5 of them are responsible for the differences in specificity between the two lactocepins (7, 40).Lactocepin purification requires release of the enzyme from the cell (30), which results from autoproteolysis of the protein in a Ca 2ϩ -free buffer (24, 25). Autoproteolysis takes place in the C-terminal part of the protein, presumably in the B domain of the protein, and results in a 145-kDa enzyme, compared to the 186-kDa cell-anchored lactocepin III (1). The action of purified lactocepins towards caseins has been studied extensively (32,33,37,38). In particular, most, if not all, of the peptides released from ␤-casein by purified lactocepin I have been identified by on-line coupling of liquid c...