Acoustic vibration method for food texture evaluation using an accelerometer sensor

A piezoelectric element has been used in an acoustic vibration method for measuring food texture. While it is inserted into a food sample, the piezoelectric element detects the vibration of a probe. The frequency response of the piezoelectric sensor used for the acoustic vibration method was evaluated with a laser Doppler vibrometer (LDV). The output voltage from the piezoelectric sensor, which was driven to vibrate at 23 different frequencies, was monitored and compared with the velocity signal obtained by the LDV. The output signal was substantially affected by the vibration frequencies. The output signals corresponded to displacement of the probe below 3 Hz, to velocity from 10 to 70 Hz, and to the acceleration force from 680 to 1500 Hz. These results clearly indicate that a piezoelectric sensor is impractical to use for the texture measurement and should be replaced with an accelerometer that always generates an acceleration signal irrespective of the applied vibration frequencies. The results also demonstrated that the previously defined texture index (TI) was misleading and overestimated the texture of food at probe vibration frequencies above 10 Hz. Our replacement of the sensor led us to define a new energy texture index (ETI). ETI measurement of several foods, including biscuit, Japanese cracker and vegetables were presented and the effects of water activity of cracker on the index were examined.

► Frequency response of a piezoelectric element was examined for food texture test.
► The element generated complex signals of displacement, velocity and acceleration.
► A piezoelectric element is not a suitable sensor for food texture evaluation.
► New energy texture index was defined using an accelerometer as a sensor.
► Several food and effects of water activity were examined by the new method.