Nowadays, digitalization is one of the main challenges the industry is facing. Affordable sensors regarding cost and user-friendliness become of major importance for companies using them on a daily basis. Thus, ultrasonic transducers are sensors that fit these requirements by means of ultrasonic waves. The modification of these waves, when propagating through food products, provides information to characterize in a non-destructive way food properties.

In this sense, the present contribution aims to illustrate the use of ultrasonic sensors for non-destructive monitoring of food properties and defects detection in Food Engineering courses from a practical point of view. To achieve that, the practical session aims to #1, determine the salt concentration in an aqueous solution and #2, detect a defect in cheese.

For the first objective, the students prepared salt solutions at different concentrations: 0, 4, 7, and 10% (w/v), and an ultrasonic signal was recorded for every solution using a LabView interface. This allows to calibrate the mathematical relationship between the ultrasonic velocity and the salt concentration. Finally, 2 more solutions of unknown salt concentration were measured with the aim of model validation.

For the second objective, 2 white cheeses were examined. Unseeing by the students, one of the cheeses was de-molded, perforated, and put back into the mold. The students measured the ultrasonic signal passing through both cheeses inside the mold and observed the differences in the signals at a glance.

After the signal acquisition, the analysis of the signal was performed. The ultrasonic signal registered consisted of two data columns that were plotted: x-axis time and y-axis voltage. From the plotted signal, the time of flight of the ultrasonic signal through the product was calculated. Furthermore, the ultrasonic equipment had installed a caliber that measured the height of the food product. By relating the time of flight and sample thickness, ultrasonic velocity through the product was calculated.

For the first objective, 4 different ultrasonic velocities were obtained and related to the salt concentration by linear regression. For the second objective, ultrasonic velocity in the cheese was calculated and after, it was used to estimate the height of the hole in the perforated cheese. To evaluate the comprehension of the experiments performed by the students, a questionnaire with the aforementioned calculations was included.

In the laboratory, the students had the opportunity to work with an ultrasonic equipment as well as to measure different foodstuffs with different compositions that were reflected on the diverse ultrasonic signals. During the signal analysis, many questions arose from the students since they were facing an ultrasonic analysis for the first time. However, after the explanation of how to perform the calculations, the understanding by students enhanced remarkably. In this sense, the reports submitted by the students showed a great understanding of the functioning of the ultrasonic system since almost every group reported a correct ultrasonic velocity for both salt solutions and cheese.

This practical lesson enabled the students to have a first approach with ultrasonic technology, allowed them to study the main parameters of a time-domain ultrasound signal, and to use these parameters to obtain information from two food products and their characterization in a fast and non-destructive way.

Keywords: Practical lesson, digitalization, sensors, ultrasound, characterization, foodstuff.