FORMATION OF PYRAZINES FROM THE MAILLARD REACTION OF GLUCOSE AND LYSINE-ALPHA-AMINE-N-15

The contribution of alpha- and epsilon-amino nitrogen atoms to pyrazin e formation in the reaction of labeled lysine with glucose was investi gated. The labeled lysine, which contained a N-15 isotope labeled at t he cr-amino group and a N-14 at the epsilon-amino group, was reacted w ith glucose at different pHs and temperatures in a dry system. A simil ar reaction mixture was also studied in an aqueous system at 180 degre es C and pH 8.5. Pyrazine, methylpyrazine, ethylpyrazine, 2,6-dimethyl pyrazine, 2,3-dimethylpyrazine, vinylpyrazine, 2-ethyl-5-methylpyrazin e, 2-ethyl-6-methylpyrazine, 2-vinyl-5-methylpyrazine, and trimethylpy razine were identified in the dry system. All pyrazines identified in the dry system were also found in the aqueous system. Two additional p yrazines, three pyridines, and one pyrrole were also observed in the a queous system. Both the alpha- and epsilon-amino groups of lysine were involved in pyrazine generation. The nitrogen atoms from alpha-amino groups of lysine react more readily with dicarbonyls to form pyrazines than the nitrogen atoms from epsilon-amino groups. The amounts of pyr azines significantly decreased as the reaction temperature decreased. Neither the reaction temperature nor the pH of the reaction mixture ha d any effect on the contribution of the two different amino groups to pyrazine formation.