Metabolic fate of peptides in a rice protein hydrolysate in rat intestine and blood after oral administration

The objective of this study was to elucidate the metabolic fate of peptides in a rice protein hydrolysate (RPH) in rats. Peptides present in RPH and its in vitro exopeptidase digest were identified using liquid chromatography-tandem mass spectrometry. One hour after an oral administration of RPH (250 mg/kg body weight), the levels of in vitro exopeptidase-resistant pyroglutamyl peptides in the lumen and ileal tissue significantly increased, whereas those of exopeptidase-susceptible peptides remained unchanged. Among them, the concentrations of pyroGlu-Leu, pyroGlu-Val, and pyroGlu-Lys significantly yet slightly increased in portal blood, while those of other hydrophilic ones (pyroGlu-Gln, pyroGlu-Glu, etc.) remained unchanged. However, all of the pyroglutamyl peptides were stable in rat ileal extract and blood plasma. These findings indicate that the pyroglutamyl peptides can enter enterocytes and resist to peptidases, while small amounts are transported to the blood, suggesting that pyroglutamyl peptides in enterocytes might be returned to the lumen.