Stability of low density lipoprotein particles affect the formation of off-flavor in thermal egg yolk

This study aimed to investigate the role of stability of low density lipoprotein (LDL) spherical particles as well as oxidation of lipids and proteins on formation of off-odor in heated egg yolk (EY). Off-odor attributes and volatile components of EY with different thermal temperature (25 °C-90 °C) were investigated by sensory evaluation, gas chromatography-mass spectrometry (GC-MS) and GC-ion mobility spectrometry (IMS). The off-flavor and volatile compounds increased significantly when EY were heated at 60 °C-65 °C. Destruction of LDL particle structure was presented by confocal laser scanning microscopy with thermal treatment at 60 °C. A positive correlation (r = 0.899, p < 0.05) was shown between oil exudation and off-odor of heated EY. Moreover, oxidation of lipids and proteins, protein aggregation, and changes of protein secondary structure (increased β-sheets and decreased α-helices) in LDL particles were all found when heating temperature rose to 65 °C. It was speculated that unstability of LDL particles resulted in the leakage of lipids; then oxidative products of lipids took part in the formation of off-odor volatiles in heated EY.