Of the ca. 20 million chemical compounds presently characterized, almost half are heterocyclic molecules. Heterocyclic molecules are significant due to their abundance in nature, as well as their chemical and biological importance. In the flavor and fragrance industry, heterocyclic compounds are of interest because of their varied occurrence in food flavors and their valuable organoleptic characteristics. Even though heterocyclic aroma chemicals are found only in minute amounts in foods, their powerful odors and low odor thresholds, as expressed by high ϕ values (see below), make them key in boosting flavors and fragrances.
The main heterocyclic aroma chemicals are oxygen-, sulfur- and nitrogencontaining rings. The oxygen-containing heterocyclic aroma chemicals belong to the oxirane, furan, pyran and oxepine groups. The sulfur-containing aroma chemicals belong to the thiophene family and, together with nitrogen, to the thiazole and dithiazine systems. Nitrogen-containing aroma chemicals belong to pyrrole, indole, pyridine, quinoline, pyrazine and quinoxaline systems, and, together with sulfur, as mentioned above, the thiazole and dithiazine families. The oxygen-containing heterocyclic aroma chemicals already have been examined (P&F magazine, May 2006, page 34). Here, the nitrogen- and sulfurcontaining aroma chemicals are studied.
Due to the highly potent odor character of a majority of the heterocyclic compounds used in flavors and fragrances, the term ϕ Value will be used for some of the materials described. A relatively new concept, ϕ Value gives a better understanding of the odor intensity of a single molecule, taking into consideration its molecular mass (MM), analogous to ε value in UV/VIS data of particular molecules.