Rheological behavior of egg yolk: Processing impacts and applications in food systems

Egg yolk (EY) is a nutrient-dense, multifunctional food ingredient with complex rheological behavior that is critical for its performance in emulsions, sauces, and baked goods. This review consolidates and analyzes current knowledge on how food processing techniques, including freezing, thermal treatments, ultrasound, high-pressure processing (HPP), microfluidization, as well as additives like hydrocolloids, alter EY rheology and its subsequent applications in food systems. Key findings reveal that processing induces structural changes (e.g., protein denaturation, aggregation, gelation) which modify key rheological properties like viscosity, viscoelasticity, and shear-thinning behavior. For instance, thermal processing above 80 °C transforms yolk into a solid-like gel, which is crucial for product texture in cooked sauces, while freezing-induced gelation can be detrimental or beneficial depending on the control of ice crystal formation. Emerging non-thermal technologies like HPP and ultrasonication offer pathways to tailor functionality, such as by enhancing interfacial elasticity in emulsions or creating novel gel structures without heat. Furthermore, additives like hydrocolloids and salts provide precise control over thermal stability and texture. A critical analysis of the literature reveals that the interplay between yolk composition, processing conditions, and rheology is central to optimizing food product quality and functionality. This review identify key knowledge gaps, particularly in understanding molecular-scale mechanisms and the lack of standardized methods, and we urge future interdisciplinary research to bridge these gaps for the targeted design of yolk-containing foods. Lastly, to address the variability in methodological approaches, we provide a framework for rheological analysis to facilitate more consistent comparisons across future studies.