Acrylamide formation in food: a mechanistic perspective

Earliest reports on the origin of acrylamide in food have confirmed asparagine as the main amino acid responsible for its formation. Available evidence suggests that sugars and other carbonyl compounds play a specific role in the decarboxylation process of asparagine, a necessary step in the generation of acrylamide. It has been proposed that Schiff base intermediate formed between asparagine and the sugar provides a low energy alternative to the decarboxylation from the intact Amadori product through generation and decomposition of oxazolidin-5-one intermediate, leading to the formation of a relatively stable azomethine ylide. Literature data indicate the propensity of such protonated ylides to undergo irreversible 1,2-prototropic shift and produce, in this case, decarboxylated Schiff bases which can easily rearrange into corresponding Amadori products. Decarboxylated Amadori products can either undergo the well known beta-elimination process initiated by the sugar moiety to produce 3-aminopropanamide and 1-deoxyglucosone or undergo 1,2-elimination initiated by the amino acid moiety to directly generate acrylamide. On the other hand, the Schiff intermediate can either hydrolyze and release 3-aminopropanamide or similarly undergo amino acid initiated 1,2-elimination to directly form acrylamide. Other thermolytic pathways to acrylamide--considered marginal at this stage--via the Strecker aldehyde, acrolein, and acrylic acid, are also addressed. Despite significant progress in the understanding of the mechanistic aspects of acrylamide formation, concrete evidence for the role of the different proposed intermediates in foods is still lacking.