Characterization of natural "cooling" compounds formed from glucose and L-proline in dark malt by application of taste dilution analysis

Gel permeation chromatography of the solvent extractables isolated from a t hermally treated glucose/ L-proline mixture and sensory analysis of the fra ctions collected led to the discovery of the presence of "cooling'' compoun ds in Maillard reactions. To characterize the key compounds imparting this cooling sensation to the oral cavity, a taste dilution analysis was perform ed by determining the taste threshold of reaction products in serial diluti ons of HPLC fractions to select the most intense "cooling'' compounds in th e complex GPC fraction of the Maillard reaction mixture. Systematic C-13-la beling experiments and GC-MS, LC-MS, and 1D- and 2D-NMR measurements, follo wed by synthesis, led to the unequivocal identification of 3-methyl-2-(1-py rralidinyl)-2-cyclopenten-1-one (3-MPC), 5-methyl-2-(1-pyrrolidinyl)-2-cycl openten-1-one (5-MPC), and 2,5-dimethyl-4-(1-pyrrolidinyl)-3(2H)-furanone ( DMPF) as the key compounds contributing the most to the cooling sensation. Although these structures were described earlier with regard to Maillard re actions, this is the first time that Maillard reaction products are reporte d to cause intense cooling sensations by degustation. Finally, the detectio n of 5-MPC (101.3 mug/kg), 3-MPC (9.4 mug/kg), and DMPF (11.5 mug/kg) in da rk malt verified their natural occurrence in thermally processed foods.