title: Degradation of milk-based bioactive peptides by yogurt fermentation bacteria.
abstract: OBJECTIVE
  To analyse the effect of cell-associated peptidases in yogurt starter culture strains Lactobacillus delbrueckii ssp. bulgaricus (LB) and Streptococcus thermophilus (ST) on milk-protein-based antimicrobial and hypotensive peptides in order to determine their survival in yogurt-type dairy foods.
  
  
  RESULTS
  The 11mer antimicrobial and 12mer hypotensive milk-protein-derived peptides were incubated with mid-log cells of LB and ST, which are required for yogurt production. Incubations were performed at pH 4.5 and 7.0, and samples removed at various time points were analysed by reversed-phase high-performance liquid chromatography (RP-HPLC). The peptides remained mostly intact at pH 4.5 in the presence of ST strains and moderately digested by exposure to LB cells. Peptide loss occurred more rapidly and was more extensive after incubation at pH 7.0.
  
  
  CONCLUSIONS
  The 11mer and 12mer bioactive peptides may be added at the end of the yogurt-making process when the pH level has dropped to 4.5, limiting the overall extent of proteolysis.
  
  
  CONCLUSIONS
  The results show the feasibility of using milk-protein-based antimicrobial and hypotensive peptides as food supplements to improve the health-promoting qualities of liquid and semi-solid dairy foods prepared by the yogurt fermentation process.
authors.affiliation: Eastern Regional Research Center, Agricultural Research Service, US Department of Agriculture, Wyndmoor, PA 19038, USA. moushumi.paul@ars.usda.gov
authors.forename: M
authors.initials: M
authors.lastname: Paul
authors.forename: G A
authors.initials: GA
authors.lastname: Somkuti
mesh_terms: D023181:Antimicrobial Cationic Peptides / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D005285:Fermentation; D006863:Hydrogen-Ion Concentration; D048668:Lactobacillus delbrueckii / Q000378:metabolism*; D008894:Milk Proteins / Q000378:metabolism*; D048249:Streptococcus thermophilus / Q000378:metabolism*; D015014:Yogurt / Q000382:microbiology*
chemical_list: D023181:Antimicrobial Cationic Peptides; D008894:Milk Proteins