Abstract
Egg albumin (from Difco) -ethyl linoleate mixture (2 : 1) was stored at 30°C, RH 80%. Damage to methionine and lysine residues, and changes of browning value (whiteness by Hunter) of the oxidized protein with the lipid in this system were estimated. On the oxidation of ethyl linoleate, PV of the lipid increased rapidly after 3-4 days and reached the maximum after 7 days, while CV increased rapidly after 5-6 days and reached the maximum after 8-9 days. Lysine residue (FDNB reactive lysine) of the oxidized protein was damaged gradually after 7 days and whiteness decreased gradually with damage to lysine. Methionine of the oxidized protein, which was determined by both of the Neumann method (iodoacetate treatment-performic acid oxidation method) and gas chromatographic method (cyanogen bromide treatment-methylthiocyanate method), was damaged rapidly after 5 days and about 70% of methionine was damaged during 12 days. From these results, it was concluded that damage to methionine arose more rapidly than damage to lysine and browning of the oxidized protein with lipids. Furthermore it was shown that the method by gas chromatography for determination of methionine residue in proteins was more convenient than the Neumann method.
