Non-invasive monitoring of potato drying by means of air-coupled ultrasound

Air-coupled ultrasound could be considered a suitable on-line technique for the non-invasive industrial testing of potato products manufactured in slices such as dried, fried or baked potato chips. Thus, the aim of the present study is to test the feasibility of air-coupled ultrasound to monitor the modifications in the physicochemical parameters of potato slices caused by drying. For that purpose, the potato slices (6 mm) were air dried (60 degrees C) for different drying times (15, 90, 180, 300 and 420 min). Air-coupled ultrasonic measurements were taken using through-transmission mode (250 kHz) and different compositional and textural parameters were measured. During drying, the ultrasonic velocity and the impedance increased significantly (p < 0.05) from 509 m/s (raw) to 673 m/s (dried for 420 min) and from 0.544 MRayl (raw) to 0.844 MRayl (dried for 420 min), respectively. Furthermore, a reduction was observed in the material attenuation, which was computed by the increase in the variation of the transmission coefficient with frequency (Delta TCf). A principal component regression (PCR) model was successfully trained and validated and it demonstrated the potential capacity of the computed ultrasonic parameters to predict the apparent elastic modulus (E) (R2 = 0.96) and the Total Relaxation Capacity (TRC) (R2 = 0.99) during the drying of potato slices. The ultrasonic analysis and experimental set-up proposed in this study may be easily implemented and tested with other products, such as dried, fried or extruded snacks based on fruits or vegetables, for industrial quality control purposes.