A new method for measurement of fruit texture

We have developed a new measurement device to characterize fruit texture. A probe with a conical or wedge tip was inserted to the fruit flesh by a piston driven by a silicon oil dispenser. The probe vibration while it was inserted into the sample was detected by a piezoelectric sensor attached directly to the probe. The voltage data were passed through 19 half-octave band filters from 0-25600 Hz. Output voltage patterns detected by the sensor showed the complex laminar structure of onion tissues. A food texture index (FTI) was calculated with an equation, FTI=Ʃ(f_mV_i)²/n, where V_i is the voltage emitted from the sensor, f_m is the mean frequency of a particular band, and n is data number, assuming that the square of voltage relates to the energy of the probe vibration. Crispness of grape flesh of nine cultivars was evaluated by the device. A wedge type probe significantly classified the nine cultivars into three distinct groups; crisp, intermediate, and non-crisp. These classifications agree with the results of sensory evaluation. Two crisp cultivars exhibited significantly higher FTI between 50 and 6400 Hz than the other two types. Non-crisp type (three cultivars) showed significantly lower FTI between 50 and 3200 Hz than the other two. Intermediate type showed FTI significantly different from those of other two types between 50 and 3200 Hz, suggesting that FTI between these two frequencies evaluates grape flesh crispness. Conventional evaluation using maximum force measured by a rheometer did not classify these three groups, suggesting that the new method distinguished different texture of grape flesh that cannot be obtained by the conventional method. Conical probe did not show such a clear discrimination among three groups, suggesting that the probe selection is important for evaluating the texture.