Release of dipeptidyl peptidase IV (DPP-IV) inhibitory peptides from milk protein isolate (MPI) during enzymatic hydrolysis

The release of dipeptidyl peptidase IV (DPP-IV) inhibitory peptides from bovine milk protein isolate (MPI) during trypsin hydrolysis was studied using a design of experiments (DOE) approach. A 3 factor×3 level DOE including temperature (40, 50 and 60°C), enzyme to substrate ratio (E:S; 0.50, 1.25 and 2.00% (w/w)) and hydrolysis time (60, 150 and 240min) was used during the generation of 15 hydrolysates (H1-H15). The degree of hydrolysis (DH) varied between 6.98±0.31 (H8) to 12.75±0.62% (H10). The DPP-IV half maximal inhibitory concentration (IC50) ranged from 0.68±0.06 (H11)/0.68±0.10 (H4) to 1.59±0.11mgmL-1 (H8). Temperature had no effect (p>0.05) on the DPP-IV IC50 value, while an increase in E:S or time significantly decreased DPP-IV IC50 value (p<0.05). The DPP-IV IC50 value of 0.69mgmL-1, predicted by response surface methodology (RSM), to be obtained with an hydrolysate generated at 50.5°C, 2% ES and 231min (H16) was similar to the experimentally obtained value (DPP-IV IC50=0.66±0.10mgmL-1, p>0.05, n=3). Following simulated gastrointestinal digestion (SGID) of H16 (H16_CorPP), the DPP-IV IC50 value increased (p<0.05) to 0.90±0.07mgmL-1. There was no significant difference between the DPP-IV IC50 value of the SGID of MPI (MPI_CorPP, 0.89±0.11mgmL-1) and that of H16_CorPP. Potent known DPP-IV inhibitory peptide sequences were identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS) within H16, some of which were also present within H16_CorPP. MPI hydrolysates may be of interest for serum glucose regulation in humans.