Bitter Peptides in Cow Milk Casein Digests with Bacterial Proteinase

Isolation and determination of amino acid sequence of the bitter peptides formed in the digestion of cow milk casein with alkaline proteinase of Bacillus subtilis were investigated. The casein digest with the enzyme was extracted with butanol and the extracted bitter peptides were fractionally purified by treating with several other organic solvents followed by subjecting to chromatography and gel-filtration. The amino acid sequence of one of the bitter peptides was determined as follows: Arg•Gly•Pro•Pro•Phe•Ileu•Val. Liberation of N-terminal Arg with trypsin or bacterial aminopeptidase did not affect the bitterness. Also, splitting off of Val and Den or Ileu•Val at the C-terminus by carboxypeptidase, or a bacterial neutral proteinase gave no influence on the bitterness. However, liberation of Arg and Gly from the peptide with bacterial aminopeptidase gave rise to_??_non bitter peptide.