Acoustic firmness measurement of differently shaped pears: Comparison of resonance indices with propagation indices

We have used a two-point acoustic sensing setup to conduct a comparative study between four resonance indices and two propagation indices for firmness evaluation of differently shaped pears. All firmness indices correlate with the Magness-Taylor penetration firmness of pears. Our proposed dual-frequency index is the most sensitive to the firmness changes and classifies pears with the highest accuracy. Except for the conventional single frequency index, the other three resonance indices and two propagation indices show a relatively higher firmness prediction capability for differently shaped pears. Accordingly, the resonance methods and the propagation methods are suitable for nondestructive detection of firmness of non-spherical pears. However, an appropriate choice of the method depends on the complexity of fruit shapes and the availability of cost-effective hardware.