Measurement of vertical and horizontal vibrations of a probe for acoustic evaluation of food texture.

Two-dimensional (vertical and horizontal) vibrations of a wedge-type probe upon food rupture were evaluated separately using two accelerometers placed perpendicular to a guide rod of a swing-arm device for texture evaluation of the flesh of three varieties of apples and three types of potato chips. Voltage signals from the accelerometers were filtered using a half-octave band-pass filter. The energy texture index (ETI), based on kinetic energy of the vertical or horizontal probe vibrations, was calculated over low to high frequency bands (no. 1-21). The spectra for the flesh of the three varieties of apples included two common peaks for vertical ETI at band no. 11 (1,120-1,600 Hz) and 19 (17,920-25,600 Hz) and horizontal ETI at band no. 1 (0-10 Hz) and 15 (4,480-6,400 Hz). The spectra for the three types of potato chips had a common ETI peak at band no. 11 (1,120-1,600 Hz) for horizontal ETI and at no. 15 (4,480-6,400 Hz) for vertical ETI. The three apple varieties gave rise to different intensities of vertical and horizontal ETIs while the two peaks were maintained. The thick potato chip type had higher vertical and horizontal ETIs than the thin and soft varieties in most bands; however, the thin type had the highest vertical ETIs only in lower bands (0-200 Hz). The soft type had the lowest vertical and horizontal ETI. The above results suggest that different food textures can be distinguished by two-dimensional vibration analyses of probe insertion into a food sample based on frequency bands.