Molecular interactions in gels prepared with egg yolk and its fractions

The behaviour of hen's egg yolk or its plasma and granules fractions, upon heating at 90 °C for 30 min in the presence of d,l-dithiothreitol (DTT), N-ethylmaleimide (NEM) or Tween 40, was studied to establish the role of disulfide covalent bonds and hydrophobic interactions between yolk protein constituents in the formation of gel network structure. The application of uniaxial compression test to gel samples indicated that the yolk and its plasma fraction exhibit a similar behaviour, regarding the involvement of disulfide bonds between their protein constituents in gel structure development, as both samples produced weak gels in the presence of DTT and NEM. The fracture properties of granules fraction gel, on the other hand, were not markedly affected by disulfide bond-splitting or sulfhydryl group-blocking reagent addition. Hydrophobic interactions appear to influence gel structure development by yolk or plasma while disulfide linkages formed between interacting protein molecules, either through sulfhydryl-disulfide interchanges or as a result of sulfhydryl groups' oxidation, appear to play a complementary role. These findings are supported by turbidity measurements of heated dispersions of yolk and its fractions and by SDS-PAGE analysis.