Advances in spectral analysis of vibrations for non-destructive determination of tomato firmness

Characteristics of fruit vibrations are related to the material properties of the fruit. A new method for spectral analysis is developed and used for the non-destructive estimation of tomato firmness. The resonant frequency o f the first elliptical mode of the tomato is related to its firmness. Howev er, the determination of the resonant frequency is not straightforward for highly damped fruits. Non-parametric smoothing is applied to the frequency spectra to obtain a robust estimate for the resonant frequency. The smoothi ng method is based on a statistical approach. The most important parameter that has to be determined is the smoothing parameter, as it determines whet her the fitted function will be (too) smooth or (too) wavy. Risk estimation is used to find the optimal value. Using the proposed algorithm, fewer rep eated measurements are needed for the assessment of the firmness of a singl e tomato. (C) 2001 Silsoe Research Institute.