Changes in structure and flavor of egg yolk gel induced by lipid migration under heating

Lipid migration is widespread in food system and has an important effect on food quality. It is urgent to explore the lipid migration in egg yolk after heating. The content of lipids in upper part (HL) was higher than that in bottom part (LL), and the lipids migration in yolk gel under heating were confirmed by MRI (T1) and T2 relaxation time of LF-NMR. Subsequently, the XDR result demonstrated the high lipid content induced the decrease in crystallinity of protein in HL part. The structures of HL part trend to be more ordered, stable (β-sheet & β-turns) and flat (α-helices) than LL part, also, more water distributed in LL part were observed by FTIR spectrum. The SEM results revealed that lipids migrated from LL to HL part, eventually lead to the protein in HL part of heated yolk gel unfold, the globular structure collapsed and become flatter. Morever, ethyl acetate, hexanal, etc. and hexanal, ethyl acetate, dimethyl-silanediol, etc. were identified as the main VOCs of LL and HL part of heated yolk gel, respectively. Lipid migration result in more lipid-specific volatiles were formed in the HL part, such as hexanal, 3-hydroxy-cyclohexanone, 2-pentyl-furan, d-limonene, 2-ethyl-1-hexanol, benzeneacetaldehyde. Lipid migration in heated yolk gel, caused by heat treatment, resulted in the changes of structure and flavor between HL and LL part.