Interpreting the “twice gelation” mechanism of a novel egg-based yoghurt through the dynamics of rheology, microstructure, and intermolecular forces

In this paper, we interpreted the "twice gelation" mechanism of egg-based yoghurt through the integrated multidimensional dynamic change analysis of rheology, microstructure, and intermolecular forces. The results showed that during the first gelation stage (i.e., thermal gelation), egg proteins underwent heat denaturation and formed crosslinks, with the main intermolecular forces involved in gel formation being disulfide bonds (∼84%). After homogenization by the colloid mill, the heat-induced gel transformed into a smooth, viscous fluid state, which subsequently turned into a weak gel as the pH continuously decreased under the effect of lactic acid bacteria fermentation. In the second gelation stage (i.e., acid gelation), the proportion of hydrophobic interactions increased from ∼12% to ∼49%, whereas the proportion of disulfide bonds decreased from ∼74% to ∼45%, indicating that hydrophobic interactions played a crucial role in the second gelation, while disulfide bonds still showed great importance in stabilizing the gel structure, although their percentage decreased significantly. In summary, egg proteins form a hard gel by heating, and this heat-induced gel has the ability to gel twice after homogenization, making it possible to form egg-based yoghurt with a fine texture and good taste under the action of lactic acid bacteria fermentation.