Pyrraline

All of the chemicals were of analytical grade, unless otherwise stated. The L-lysine, D-glucose, NaCl, xanthan gum, and gum arabic were purchased from Macklin Biochemical Co., Ltd. (Shanghai, China). The acetonitrile and formic acid of HPLC grade were acquired from Merck (Darmstadt, Germany). A solid-phase extraction cartridge, Cleanert PEP-2 (200 mg/6 mL, Bonna-Agela Technologies Inc., Tianjin, China), was used for the purification of the MR products. The pyrraline (purity >99.99%) and 3-deoxyglucosone (purity >99.99%) were supplied by Toronto Research Chemicals (North York, Ontario, Canada). The starches were obtained from Ingredion Incorporated (Shanghai, China).

The three dipeptides (Lys-Gly, Lys-Ala, Lys-Phe) and three tripeptides (Lys-Gly-Gly, Lys-Gly-Ala, Lys-Gly-Phe) were from LifeTein LLC. (Beijing, China). Standards of 3-Deoxyglucosone (3-DG, purity > 99.99%) and pyrraline (purity > 99.99%) were from Toronto Research Chemicals (Toronto, ON, Canada). Formic acid (for LC-MS, 99%) was from Aladdin Biochemical Technology Co., Ltd. (Shanghai, China). Solid-phase extraction (SPE) cartridges (Cleanert PEP-2, 200 mg/6 ml) for purification were from Bonna-Agela Technologies Co., Ltd. (Tianjin, China). Chromatographic grade acetonitrile was from Merck (Darmstadt, Germany). Pepsin, pronase E, and prolidase were from Sigma-Aldrich (Shanghai, China). All other reagents were of analytical grade from Macklin Inc. (Shanghai, China).