Screening of key dipeptidyl peptidase IV (DPP-IV) inhibitory peptides from casein hydrolysates based on peptidomics, chemometrics, recombination, and omission experiments

Casein is considered a good source for preparing dipeptidyl-peptidase IV (DPP-IV) inhibitory peptides. However, the contributions of identified DPP-IV inhibitory peptides in actual casein hydrolysates to the overall activities remain unclear. This study screened the key DPP-IV inhibitory peptides in the casein hydrolysate generated with proteaxh (CXH) by peptidomics, chemometrics, recombination, and omission experiments. Our results showed that Xaa-Pro-Xaa-Pro-type (XPXP-type) peptides with 4–8 residues and other Xaa-Pro-type (XP-type) peptides with 2–5 residues, especially containing an N-terminal residue (Ile, Leu, Val, Ala, Met, Phe, Gly, and Tyr) contributed greatly to CXH. CXH (900 mg/kg) showed an obvious hypoglycemic effect in vivo. Nine novel DPP-IV inhibitory peptides (MPIQ, APFPEVF, MPIQA, APFP, YPE, MPFP, LPLP, FPEVF, and APFPEV) were identified. Twenty screened XP-type peptides accounted for 39.69 % and 45.16 % of the DPP-IV inhibitory activities of CXH and its digest, and LPVP showed the highest contribution value (over 9 %).