The characteristic aromas of many natural foodstuffs of plant and animal origin are strongly influenced by trace quantities of volatile nitrogen compounds like amines, imines, pyrazines and pyrroles. The biosynthesis of these and related compounds begins with the conversion of nitrogen gas or nitrate into ammonia. Many nitrogenous volatiles are formed as minor byproducts of amino acid biosynthesis. Some heteroaromatic compounds like pyrazines also appear to be formed under biogenic conditions by a combination of enzyme-catalyzed and non-enzyme-catalyzed reactions. The overall driving force for the latter reactions is probably an exothermic, irreversible final step leading ultimately to stable aromatic nuclei.
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