In this work egg white was used to study the effect of common food processing conditions on in vitro
protein digestibility and on the modification of amino acid residues. Egg white was treated at 20 8C and
100 8C, varying pH (2–12), and zero and high-salt concentrations (0 mM, 200 mM). The digestibility
assays confirmed previous findings that exposure of egg white to high temperatures increased
digestibility markedly. However, the effects of pH and salt concentrations were found to be minimal.
Proteomic analysis was utilised to map amino acid modifications, revealing that increased digestibility in
heated egg white comes at the cost of a higher degree of amino acid residue-level modification. The
predominant modifications were found to be dehydration and deamidation reactions that increased
with increasing heat exposure time. The effects of the Maillard reaction on digestibility and amino acid
modification were also determined for egg white in the presence of glucose and methylglyoxal.
Proteomic assessment clearly revealed a high degree of modification of up to 38% of available arginine
residues in the presence of methylglyoxal. An important correlation was therefore established between
increased levels of Maillard reaction products and a decrease in the nutritional value of egg white.