Changes in Protein Fluorescence in a Lipid-Protein Co-oxidizing Oleogel

High and low levels of lipid-induced protein oxidation (tuned by the addition of 0%-8.4% water) were investigated in oleogels, using excitation-emission matrix (EEM) fluorescence spectroscopy, coupled with a partial least-squares (PLS) regression and lipid hydroperoxide data. In high-level oxidation models, the intrinsic tryptophan fluorescence decreased and the emission maxima increased from 352.5 to 356.0 nm indicating the presence of protein modifications, which was further supported by size-exclusion chromatography. PLS recognized 3 latent components, with several excitation-emission points of interest. These apparent compounds include a region associated with radical mediated protein modifications (approximately 325 and 410 nm), lipid oxidation product adducts (approximately 350 nm and 420-425 nm), and malondialdehyde adducts (approximately 375 and 425 nm). The separate evaluation of these apparent compounds, at a 420 nm emission, indicated that lipid oxidation promotes protein lipid adduct fluorescence at high water levels, rather than radical mediated protein fluorescence.