Abstract: Yolk gelation occurs when stored at temperatures below ?6 ℃, which will affect yolk application in food processing. The gelation of yolk frozen for 180 d was characterized by rheological properties, and the physicochemical properties, water distribution and secondary structure were analyzed to further explore the cause of yolk gelation. Apparent viscosity, viscosity coefficient (K) value, elasticity modulus (G’) and viscous module (G’’) in yolk were significantly increased, while flow index (n) value and loss tangent (tan δ) were significantly decreased during frozen storage, suggesting that freezing led to serious gelation of yolk. Yolk gelation was caused by the increased average particle size and surface hydrophobicity, the decreased total sulfhydryl and the change in moisture distribution, and especially by the reduced freezable water content in yolk; meanwhile, the secondary structure transformation from a disordered to an ordered state of yolk proteins also promoted yolk protein aggregation and consequently induced yolk gelation. The cause of yolk gelation reported in this study provides a theoretical basis for further improving yolk gelation during freezing process.

Key words: yolk, frozen storage, gelation, causal analysis