β-casomorphins are found in cheeses made from bovine milk; their concentrations are higher in mould cheeses (e.g. Brie, Rokpol) than in semi-hard cheeses (e.g. Edam, Gouda and Kasztelan).
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Casein has been documented to break down in the stomach to produce the peptide casomorphin (above stated that "Human digestion may break down casomorphins into inactive dipeptides by the enzyme dipeptidyl peptidase-4"), an opioid that acts as a histamine releaser.