PRECURSORS OF ETHYLDIMETHYLPYRAZINE ISOMERS AND 2,3-DIETHYL-5-METHYLPYRAZINE FORMED IN ROASTED BEEF

Reaction systems (pH 5.6) containing water-soluble substances of beef meat in various combinations were heated for 7 min at 180-degrees-C. Lack of alanine in a mixture consisting of free amino acids, monosaccharides, lactic acid, carnosine and creatine strongly inhibited the formation of 2-ethyl-3,6-dimethylpyrazine (I), 2-ethyl-3,5-dimethylpyrazine (II), 2-ethyl-5,6-dimethylpyrazine (III) and 2,3-diethyl-5-methylpyrazine (IV). Carnosine as well as lactic acid stimulated the formation of the four pyrazines in the reaction system fructose/alanine, but the most effective model was obtained when, in the latter binary mixture, fructose was replaced by 2-oxopropanal. In all reactions pyrazine I was the major product but, on the basis of its much lower odour threshold, pyrazine II was the most important odorant of the three ethyldimethylpyrazines.