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