Determination of the gelation mechanism of freeze-thawed hen egg yolk

Abstract

A study of yolks stored up to 168 d at −20 °C was conducted to determine the gelation behavior and mechanism of freeze-thawed yolk. Methods used were rheology, native and sodium dodecyl sulfate polyacrylamide gel electrophoresis (native-and SDS-PAGE), differential scanning calorimetry (DSC), transmission electron microscopy (TEM), particle size analysis, and proton nuclear magnetic resonance (1H NMR) spectroscopy for matrix mobility. Results indicate that both constituents of plasma and granules contributed to gelation of yolk under freezing. PAGE analyses suggest that granular proteins participated in aggregation during freeze-thaw. Increasing gel strength and particle size and decreasing water and lipid-water mobility indicate that lipoproteins or apolipoproteins aggregated. At storage times ≥84 d, increased protein and lipid mobility, the detection of smaller particles, and secondarily increased gel strength suggest the liberation of protein or lipoprotein components from previously formed aggregates and further aggregation of these constituents. Disruption of the gelled yolk matrix observed with TEM supported that ice crystal formation was required for gelation to occur. A two-stage dynamic gelation model is thus proposed.

Determination of gelation mechanism and prevention methods of frozen-thawed hen egg yolk

“…This finding shows that both plasma and granules contribute to gel formation and strength in frozen-thawed egg yolk, and aggregations involving larger quantity of granules with other plasma components might have enhanced the gel stability due to the higher proportion of the larger granule size. Au et al 13 found an increase in particle size with extended freezing storage, indicating that yolk remained a dynamic system even at -20°C and that aggregations of lipoproteins continue as the states of water changes. In gelled yolk, the amount of granules was found to have direct influence on the force required to change the solid-like behavior of the gel into a viscous liquid 13 .…”

“…Au et al 13 found an increase in particle size with extended freezing storage, indicating that yolk remained a dynamic system even at -20°C and that aggregations of lipoproteins continue as the states of water changes. In gelled yolk, the amount of granules was found to have direct influence on the force required to change the solid-like behavior of the gel into a viscous liquid 13 .…”

“…Samples for rheology were prepared following a method by Au et al 13 cooling rate of 0.3°C/min, the yolks were held in the apparatus for another hour before the mold plate was removed and sealed in a vacuum bag to reduce freezer burn. The samples were then stored in a -20°C freezer for 5 weeks.…”

“…Within the linear viscoelastic region (LVR), in which G' is constant, the material macrostructure has not been deformed 13 . As shown on Figure 2.2A, G' increased significantly (p<0.05) with the increasing amount of granules in the system.…”

“…The most recent study on the effect of prolonged freezing storage on egg yolk gelation suggested the occurrence of two-stage gelation, which involved aggregation of lipoprotein particles resulting from water removal during slow freezing in the first stage (d 1-28), and release and re-aggregation between or within the previously aggregated proteins in the second stage (between d 28-84) forming a stronger gel network 13 . The author also suggested that granules/HDL particles were also involved in the aggregation, and various methods including evaluations of particle size, matrix mobility, protein aggregation and microstructure were able to show that these components played a role in gelation.…”