Identification of short-chain pyroglutamyl peptides in Japanese salted fermented soy paste (miso) and their anti-obesity effect
Miso, a paste of salted fermented soybean, is a seasoning used extensively in traditional Japanese cuisine. Herein, pyroglutamyl peptides present in miso were identified by a liquid chromatography-tandem mass spectrometry (LC-MS/MS), detecting precursor ions, which generated immonium ion of pyroglutamyl residue. By using this method, 13 pyroglutamyl peptides were identified in four types of miso. Administration of the water extract prepared from 0.6 g soybean miso/kg body weight/day significantly suppressed high fat diet-induced weight gain. A similar effect was exerted by the hydrophobic pyroglutamyl peptide fraction, including pyroglutamyl proline (pEP), pEV, pEI, and pEL. Administration of a mixture of synthetic pEP, pEV, pEI, and pEL in a ratio to that in miso or pEL alone also suppressed the weight gain in a dose dependent manner. These results suggest that the short-chain hydrophobic pyroglutamyl peptides present in miso are effective in suppressing high fat diet-induced obesity.