Characterization of an intense bitter-tasting 1H,4H-quinolizinium-7-olate by application of the taste dilution analysis, a novel bioassay for the screening and identification of taste-active compounds in foods

Thermal treatment of aqueous solutions of xylose and primary amino acids le d to rapid development of a bitter taste of the reaction mixture. To charac terize the key compound causing this bitter taste, a novel bioassay, which is based on the determination of the taste threshold of reaction products i n serial dilutions of HPLC fractions, was developed to select the most inte nse taste compounds in the complex mixture of Maillard reaction products. B y application of this so-called taste dilution analysis (TDA) 21 fractions were obtained, among which 1 fraction was evaluated with by far the highest taste impact. Carefully planned LC-MS as well as 1D and 2D NMR experiments were, therefore, focused on the compound contributing the most to the inte nse bitter taste of the Maillard mixture and led to its unequivocal identif ication as the previously unknown 3-(2-furyl)-8-[(2-furyl)methyl]4-hydroxym ethyl-1-oxo-1H,4H-quinolizinium-7-olate. This novel compound, which we name quinizolate, exhibited an intense bitter taste at an extraordinarily low d etection threshold of 0.00025 mmol/kg of water. As this novel taste compoun d was found to have 2000- and 28-fold lower threshold concentrations than t he standard bitter compounds caffeine and quinine hydrochloride, respective ly, quinizolate might be one;of the most intense bitter compounds reported so far.