Mechanistic studies on the formation of pyrazines by Maillard reaction between l-ascorbic acid and l-glutamic acid

The formation mechanism of pyrazine aroma compounds in the reaction between 1,4-13C-labeled l-ascorbic acid and l-glutamic acid was investigated. MS data indicated that the C-1 of l-ascorbic acid was not involved in the pyrazine formation. The α-amino carbonyl or α-amino hydroxy compounds were found to be the precursors of pyrazines. l-Glutamic acid could release ammonia when heated in aqueous solution. During the thermal degradation of l-ascorbic acid, some active intermediates such as acetol, hydroxybutadione and butanedione could be produced. These intermediates reacted with ammonia to generate α-amino carbonyl or α-amino hydroxy compounds, which then formed pyrazines. The odor quality of the pyrazine aroma compounds generated from l-ascorbic acid and l-glutamic acid was evaluated. The pyrazines may contribute to the toasted, roasted, nutty and burnt smells.