Fortification of milk with iron-ascorbate promotes lysine glycation and tryptophan oxidation
2002
Leclere, Juliette | Birlouez-Aragon, Ines | Meli, Michael
Infant formulas are supplemented with iron and ascorbate for nutritional purposes, but activation of the advanced Maillard reaction by iron and production of hydroxyl radicals by the iron-ascorbate system may damage the proteins with possible nutritional loss. In this study, we evaluate the deleterious actions of iron and ascorbate, namely lysine damage and tryptophan oxidation on whey-lactose samples incubated at 60 °C. Iron-catalysed ascorbate oxidation enhanced lysine blockage mainly by ascorbylation, whereas lactosylation was little influenced. A three-fold increase in the accumulation rate of fluorescent advanced Maillard products (AMP) was observed in the presence of iron/ascorbate and AMP fluorescence was well correlated to carboxymethyllysine concentration in the samples. The tryptophan degradation rate was 2.5-fold higher in the presence of iron-ascorbate and the loss of this amino-acid was exponentially correlated with AMP fluorescence, similarly whatever iron-ascorbate was present or not. Application of milder heat treatments to infant formulas would allow to decrease the extent of these undesirable reactions.
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