IDENTIFICATION OF DIALKYLPYRAZINES OFF FLAVORS IN OAK WOOD.

Abstract

Volatile extractive compounds from high quality oak wood (Quercus sp.) are responsible for important pleasant olfactory notes, such as coconut, wood, vanilla, caramel, and spice. Recently, a new off-flavor reminiscent of rancid butter was detected in oak wood. Using gas chromatography-olfactometry (GC-O) coupled to several detection modes, as nitrogen-phosphorus detection (GC-O-NPD) or mass spectrometry (GC-O-MS), and multidimensional GC-O coupled to time-of-flight mass spectrometry (MDGC-O-TOF-MS), six compounds containing nitrogen atoms were identified. The volatiles were suggested to belong to 2,5-disubstituted pyrazines family, which was confirmed by comparison with synthetic reference compounds. For this purpose, the symmetric and dissymmetric 2,5-dialkylpyrazines were prepared from methyl esters of corresponding aliphatic amino acids (Val, Leu, and Ile) by a three step - one pot reaction under mild reducing conditions. Organoleptic descriptors and odor detection thresholds were also determined, whereas a bacterial origin explaining these off flavors was hypothesized.