The acidification of food has as objective to decrease pH in order to reduce the microorganism development and the thermal processes severity. This process is described by two phenomena: mass transfer and acid dissociation equilibrium. The ultrasound technology has been very useful for accelerating many mass transfer unit operations as hydration, drying and extraction. However, this emerging technology has not been used yet for improving the acidification process. For that reason, the aim of this work was to study the acidification kinetics of two model food with similar composition, but with different structure using the ultrasound technology. For which, yellow melon cylinders and melon pulp – agar cylinders of 1.5 cm of diameter and 4 cm of height were acidified with and without ultrasound (41 W/L of volumetric power and 20 kHz of frequency) in a citric acid solution (0.2 %w/w) at 25 °C. The data was fit to a first order equation whose parameters (acidification rate and equilibrium pH) were compared. As results, the acidification process was accelerated by the ultrasound technology, increasing the acidification rate almost 37 % for the melon cylinders and 11 % for the melon-agar cylinders. The equilibrium pH was reduced almost 9.6 % in both the studied structures. The acidification enhancement was attributed to the ultrasound direct (“sponge effect”) and indirect effects (micro channel formation). In addition, the ultrasound could have reduced the cell H+ proton control capacity (buffer effect) due to cell membrane disruption. Moreover, the ultrasound might increase the acid dissociation, increasing the H+ concentration, and thus reducing the equilibrium pH. In conclusion, the ultrasound can be used for improving the food acidification, reducing the process time.