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 pyrazine formation in the reaction of labeled lysine with glucose was investigated. The labeled lysine, which contained a N-15 isotope labeled at the cr-amino group and a N-14 at the epsilon-amino group, was reacted with glucose at different pHs and temperatures in a dry system. A similar reaction mixture was also studied in an aqueous system at 180 degrees C and pH 8.5. Pyrazine, methylpyrazine, ethylpyrazine, 2,6-dimethylpyrazine, 2,3-dimethylpyrazine, vinylpyrazine, 2-ethyl-5-methylpyrazine, 2-ethyl-6-methylpyrazine, 2-vinyl-5-methylpyrazine, and trimethylpyrazine were identified in the dry system. All pyrazines identified in the dry system were also found in the aqueous system. Two additional pyrazines, three pyridines, and one pyrrole were also observed in the aqueous 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 pyrazines significantly decreased as the reaction temperature decreased. Neither the reaction temperature nor the pH of the reaction mixture had any effect on the contribution of the two different amino groups to pyrazine formation.