This work aimed to describe the acidification process of two specific model foods using the ultrasound technology, as well as to evaluate the changes on its viscoelasticity properties. For that, two types of model food were used, with similar composition but different structures: natural melon cylinders and restructured melon-agar cylinders. The acidification process was performed using a citric acid solution (0.2% w/w) assisted with and without ultrasound (40 W/L of volumetric power and 20 kHz of frequency) at constant temperature (25 °C). In addition, the stress relaxation analysis was performed on the cylinders in order to evaluate the changes on the viscoelastic properties. As a result, both ultrasound processing and the different structural conformation of the model foods affected the acidification kinetics, being improved by ultrasound. Further, the acidification process with and without ultrasound affected the mechanical properties of both products, reducing their elasticity. The relaxation data could be described by a Maxwell model with two bodies and a residual spring, providing a possible explanation of the association between the mechanical model parameters and the microstructural conformation of both studied cases. © 2017 Elsevier Ltd