Freeze–thaw gelation of hen's egg yolk low density lipoprotein

Abstract

The freeze-thaw gelation of hen's egg yolk low density lipoprotein (1.d.l.) has been examined by viscometry, agarose gel filtration, electron spin resonance spectroscopy, electron microscopy and differential scanning calorimetry. The data indicate that the core lipids, the hydrocarbon chains of interfacial lipids of 1.d.l. and the sulphydryl, imino, amino and tyrosine groups in the side chains of 1.d.l. peptides are not directly involved in the gelation mechanisms. The gelation is caused by non-specific aggregation due to cross-linking of peptides and/or phospholipid polar head groups of adjacent 1.d.l. particles. During freezing, interparticle contacts are formed and strengthened as transformation of solvent water into ice increases the concentration of the particles. Salt and sugar additives inhibit large increases in concentrations of 1.d.l. during freezing and prevent gelation by helping to increase solvation of interfacial regions of the 1.d.l. particles. Agents that induce large viscosity increases in the 1.d.l. sols before freezing may act by producing a local conformational change in 1.d.l. protein and/or disrupting lipid-protein bonds.

Determination of the Gelation Mechanism of Freeze–Thawed Hen Egg Yolk

“…Most researchers were in agreement that dehydration of molecules is the first step in freeze-thaw gelation (Chang, Powrie, & Fennema, 1977;Kamat, Graham, Barratt, & Stubbs, 1976;Lovelock, 1957;Martin, Augustyniak, & Cook, 1964;Palmer, Ijichi, & Roff, 1970;Sato & Aoki, 1975;Telis & Kieckbusch, 1997;Wakamatu & Sato, 1980). Jaax and Travnicek (1968) and showed that slow cooling rates must be employed to induce gelation, as fast freezing of yolk in liquid nitrogen or oxygen resulted in little to no change of fluidity even with extended storage in low temperatures (33-49 d in -20°C).…”

“…The first observation of freeze-thaw yolk gelation, as well as its inhibition by sucrose, was made by . Subsequent studies have confirmed reduced gelation via addition of other sugars such as fructose, sodium chloride and other salts, and proteolytic enzymes such as papain (Jaax & Travnicek, 1968;Kamat, Graham, Barratt, & Stubbs, 1976;Nowak, Powrie, & Fennema, 1966;Wakamatu & Sato, 1980;Wakamatu, Sato, & Saito, 1983).…”

“…Conversely, other studies showed that LDL aggregation was a result of conformational changes in the protein and phospholipid moieties of LDL, not the liberation of LDL components (Lovelock, 1957;Wakamatu & Sato, 1980;Wakamatu, Sato, & Saito, 1983). Kamat, Graham, Barratt, and Stubbs (1976) suggested that charge, hydration, and steric factors associated with the phospholipids and peptides of the LDL surface were the dominant forces contributing to aggregation.…”

“…Scanning conditions were modified from Kamat, Graham, Barratt, and Stubbs (1976) and Wakamatu, Sato, and Saito (1983). Each sample was held for 1 min at 25°C, cooled to -30°C at 10°C/min and held at that temperature for 1 min, then heated from -30°C to 25°C at 10°C/min.…”

Effect of NaCl Penetration Rate on the Granulation and Oil-Off of the Yolk of Salted Duck Egg.

“…With heat (Woodward & Cotterill, 1987a, b;Woodward, 1988) or freeze-thawing (Kamat et al, 1976;Chang et al, l 977) treatments, egg yolk may become viscous and thick, a condition known as gelation. The state of the yolk is also affected by salt even at room temperature (Mahadevan et al, 1969;Harrison & Cunningham, 1986).…”