2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) formation and fate: an example of the coordinate contribution of lipid oxidation and Maillard reaction to the production and elimination of processing-related food toxicants
2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is produced by reaction of phenylacetaldehyde, the Strecker aldehyde of phenylalanine, with creati(ni)ne in the presence of formaldehyde and ammonia, which are formed in situ. Traditionally, the carbonyl compounds required for the formation of the PhIP ring were considered to be produced as a consequence of Maillard reaction between phenylalanine and carbohydrates. This review collects all recent evidence suggesting that lipids can also contribute to the Strecker degradation of phenylalanine and the formation of formaldehyde analogously to carbohydrates. Furthermore, lipid-derived reactive carbonyls not only contribute to PhIP formation but they can also be involved in PhIP fate observed in the presence of oxidized oils. This role has not been yet investigated for carbohydrate-derived reactive carbonyls but it might be hypothesised to take place because of the decrease of PhIP observed when an excess of monosaccharides is employed to study PhIP formation. All these results suggest that carbohydrates and lipids can contribute simultaneously to PhIP formation and fate. This is another example of the simultaneous contribution of both lipids and carbohydrates to the carbonyl chemistry that takes place in foods upon processing and/or storage. Furthermore, many of these conclusions can also be extended to the formation of other aminoimidazoazarenes with an imidazopyridine structure.