Influence of fermentation temperature and autolysis on ACE-inhibitory activity and peptide profiles of milk fermented by selected strains of Lactobacillus helveticus and Lactococcus lactis

Bovine milk was fermented with single strains of Lc. lactis or Lb. helveticus at three temperatures around the optimum for each species. Fermentation was stopped at pH 4.6 and 4.3/4.0, and the products were stored at 5 °C for 1 and 7 days. The extent of lysis was examined by release of X-prolyldipeptidyl aminopeptidase activity, and the angiotensin-I-converting enzyme- (ACE-) inhibitory activity and peptide profiles of the products were determined. Fermentation temperature significantly influenced the bacterial growth, extent of lysis, and ACE-inhibitory activity. ACE-inhibitory activity was high at all temperatures, and slightly higher at the optimal growth temperature, whereas the extent of lysis was highest at a suboptimal growth temperature. Peptide profiles were marginally affected by temperature and cell lysis. The major peptides were identified, including a number of known ACE-inhibitory peptides. Our results suggest that the cell wall proteinase was the primary catalyst in release of ACE-inhibitory peptides.