Multi-scale imaging of protein oxidation in mayonnaise

In mayonnaise, lipid and protein oxidation are closely related and the interplay between them is critical for understanding the chemical shelf-life stability of mayonnaise. This is in particular the case for comprehending the role of low-density lipoprotein (LDL) particles as a main emulsifier. Here, we monitored oxidation and the concomitant aggregation of LDLs by bright field light microscopy and cryogenic transmission electron microscopy. We further probed the formation of protein radicals and protein oxidation by imaging the accumulation of a water-soluble fluorescent spintrap and protein autofluorescence. The effect of variation of pH and addition of EDTA on accumulation of spintraps validated that protein radicals were induced by lipid radicals. We observed protein radical formation at both the oil/water droplet interface and in the continuous phase. Our data suggests two main pathways of oxidative protein radical formation in LDL particles: at the droplet interface, induced by lipid free radicals formed in oil droplets, and in the continuous phase induced by an independent LDL-specific mechanism.