β-Casomorphin immunoreactive materials in cows' milk incubated with various bacterial species

To obtain information about the possible release of beta-casomorphins from beta-casein under in vitro conditions, cows' milk was incubated with 13 strains of Gram-negative or Gram-positive bacterial species isolated from bovine milk. After incubation periods of 1-24 d, milk samples were assayed for beta-casomorphin-4, -5, -6 or -7 immunoreactive materials. In general, no beta-casomorphin immunoreactive material was found in samples incubated with non-caseolytic strains, e.g. Pseudomonas putida or Streptococcus faecalis subsp. faecalis; however, high levels were found in several samples incubated with caseolytic strains, e.g. Ps. aeruginosa or Bacillus cereus. When such materials were present, the amounts of beta-casomorphin-4, -6 or -7 greatly exceeded beta-casomorphin-5 immunoreactivity. It was concluded that while some of these materials probably represented authentic beta-casomorphins, others were more likely to be beta-casomorphin precursors.