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

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Abstract
SUMMARY: To obtain information about the possible release of β-casomorphins from β-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 β-casomorphin-4, -5, -6 or -7 immunoreactive materials. In general, no β-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 β-casomorphin-4, -6 or -7 greatly exceeded β-casomorphin-5 immunoreactivity. It was concluded that while some of these materials probably represented authentic β-casomorphins, others were more likely to be β-casomorphin precursors.