In order to obtain a soft-textured protein gel suitable for the
elderly, the cod protein gel was prepared by improving the protein
flexibility under ultrasound treatment. It has been found that the
increase in ultrasonic power, protein flexibility, particle size,
ζ-potential, surface hydrophobicity, and α-helix content
of preheated cod protein exhibited an increasing trend. The improvement
of protein flexibility promoted uniformity and density of the gel
network, water retention, and texture properties. The flexibility
of preheated cod protein increased to 0.189, the water holding capacity
of the gel reached up to 99.41%, and the hardness increased to 49.12
g, as the ultrasonic power level increased to 400 W. Protein flexibility
was correlated well with the cohesiveness of the gel. The storage
modulus (G′) initially decreased and then
increased during the heating–cooling process. The attractive
forces forming between the flexible protein molecules during cooling
in the ultrasound treatment groups promoted protein self-assembly
aggregation and formed the cod protein gel. The gel obtained at 100–400
W could be categorized as Level 6soft and bite-sized according
to the International Dysphagia Diet Standardization Initiative (IDDSI)
framework, indicating that the cod protein gel has potential as an
easy-to-swallow diet for the elderly.