A process to produce IPP from a protein source whereby the protein source comprises a protein having the -I-P-P- sequence and having in the protein amino acid sequence at least 6 times more -I-P-P- present than -V-P-P- (molar basis) which comprises hydrolysing the protein source to liberate at least 40% of the I-P-P- sequence into the peptide IPP and whereby a proteolytic enzyme is used which cleaves at the carboxy-terminus of proline residues present in the protein source, the enzyme is preferably a proline specific endoprotease or proline specific oligopeptidase, more preferably a proline specific endoprotease, and optionally an amino peptidase.