Detailed Investigation of the Production of the Bread Flavor Component 6-Acetyl-1,2,3,4-tetrahydropyridine in Proline/1,3-Dihydroxyacetone Model Systems

Abstract

The production of 6-acetyl-1,2,3,4-tetrahydropyridine (ATHP), an important Maillard flavor component, in the reaction of l-(−)-proline and 1,3-dihydroxyacetone was investigated as a function of different reaction conditions. The two major side products from the reaction were identified as 5-acetyl-6-methyl-2,3-dihydro-1H-pyrrolizine and 5-acetyl-6-hydroxymethyl-2,3-dihydro-1H-pyrrolizine, the last one being a new compound described here for the first time. A maximum yield of ATHP of 2.7 mol % from l-(−)-proline and 1,3-dihydroxyacetone was noted at 130 °C in the presence of 2 equiv of sodium bisulfite. The role of sodium bisulfite as a reducing species, and as a stabilizing agent for 6-acetyl-1,2,3,4-tetrahydropyridine, was clarified. In view of the new data obtained, the hypothesized mechanism of formation of 6-acetyl-1,2,3,4-tetrahydropyridine was confirmed, and the reaction mechanisms leading to 2,3-dihydro-1H-pyrrolizines were reconsidered. Keywords: 6-Acetyl-1,2,3,4-tetrahydropyridine; bread flavor; 2,3-dihydro-1H-pyrrolizine; model reaction; Maillard flavor