Activity-Guided Screening and Identification of Natural 'Cooling' Compounds Formed from Carbohydrates and L-proline in Beer Malt

摘要

Gel permeation chromatography (GPC) of the solvent-extractables isolated from a thermally treated glucose/L-proline mixture and sensory analysis of the fractions collected led to the discovery of the presence of "cooling" compounds in Maillard reactions. To characterize the compounds imparting this oral cooling sensation, the Taste Dilution Analysis was applied to the cooling-active GPC fraction by determining the taste threshold of reaction products in serial dilutions of HPLC fractions. MS, NMR, [~(13)C] labeling experiments, followed by synthesis led to unequivocal identification of 3-methyl-2-(1-pyrrolidinyl)-2-cyclopenten-1-one (3-MPC), 5-methyl-2(1-pyrrolidinyl)-2-cyclopenten-1-one (5-MPC) and 2,5-dimethyl-4-(1-pyrrolidinyl)-3(2H)-furanone (3(2H)-DMPF) as the most intense "cooling" compounds formed from hexoses. Comparative studies on pentose/L-proline mixtures led to the identification of the odorless 5-methyl-4-(1-pyrrolidinyl)-3(2H)-furanone (3(2H)-MPF), exhibiting a "cooling" sensation at low concentrations of 1.5-3.0 mg/kg (water), as one of the most active "cooling" agents reported so far. To the best of our knowledge, these are the first Maillard reaction products reported to cause intense cooling sensations by degustation. Finally, the detection of 5-MPC, 3-MPC, 3(2H)-DMPF, and 3(2H)-MPF in dark roasted beer malts verified their natural occurence in thermally processed foods and demonstrated 3(2H)-MPF as the most active, odorless cooling agent reported so far in nature.