Network structure of response to freeze-thaw cycles in egg white protein gels filled with emulsion: Digestive kinetics regulated by the state of water and embedded oil

In this paper, we focused on the effects of freeze-thaw treatment on the network structure of egg white protein (EWP) emulsion-filled gel (EFG). The freeze-thaw stability of EFG based on egg white protein was analyzed in terms of microstructure, digestive dynamics and processing properties in this work. The results showed that the initial spatial distribution of oil droplets and fine network of gel were damaged during freeze-thaw cycles observed by confocal laser scanning microscopy (CLSM). These phenomena led to the rising of swelling ratio (from 9.882% ± 0.535%–34.985% ± 1.843%) and the change of acid uptake process, which affected the pH value and pepsin activity inside gel. The effect of freeze-thaw cycles on amino acids release during digestion was evaluated by the model of digestive kinetics. Meanwhile, the characteristics of emulsion and gel matrix were detected, illustrating the effect of the ions and percentage of oil on gel subjected to freezing. With the repeats of freeze-thaw treatment, the initial gel network was reorganized for the thicker chain-like structure with higher cohesiveness (from 0.44 ± 0.014 to 0.75 ± 0.041), while ions could be used as stabilizer in frozen. Furthermore, the lower relaxation time proved the improved stability caused by ions, which resulted from the enhanced limitation of network structure to fillings. These findings provided valuable information on the relationship between the freeze-thaw stability of emulsion-filled gel and in vitro digestion, with a view to broader application in the direction of future fat replacement.