Malondialdehyde treatment reduced immunoreactivity of amandin and delayed its digestion

The secondary products of lipid oxidation are one of the main factors inducing protein oxidation. The effects of oxidation treatment with malondialdehyde (MDA) on immunoreactivity of amandin and its digestion were studied. The rabbit IgG binding ability of amandin was analyzed by western blotting, and the changes of oxidation on amandin and the immunoreactivity during digestion of amandin with different degrees of oxidation were investigated in combination with an almond allergen ELISA kit. Alteration of linear epitopes of amandin by oxidation was investigated by LC-MS/MS. The results showed that immunoreactivity of amandin was significantly reduced after 1 and 100 mmol/L MDA treatment. However, the 1 mmol/L MDA treatment was owing to cleavage of linear epitope peptide in amandin and oxidation of the active amino acid. The 100 mmol/L MDA treatment was due to aggregation of amandin and significant decrease in its solubility. Oxidation also reduced digestibility of amandin and significantly affected immunoreactivity during digestion. LC-MS/MS also identified four oxidation-prone methionine sites (aa 264-274, 298-308, 220-240 and 275-297) in Gamma conglutinin 1. MDA treatment reduced the immunoreactivity of amandin. MDA treatment also led to protein aggregation, which slowed down the digestion of amandin and altered immunoreactivity of amandin during digestion.