3. Results and discussion
The photographs in Fig. 2 show the internal appearance of pineapples graded into three maturity levels and a set of marbled fruit. Photograph 1 represents the class A of greater than 50% translucent yellow, photograph 2 for class B having 25–50% translucent yellow, photograph 3 representing class C of less than 25%, while photograph 4 depicts a marbling defect.The acoustic impulse response of a pineapple sample showing three distinct resonant peaks is shown in Fig. 3.The data is in agreement with those produced by Valente et al. (2001) and Chen and De Baerdemaeker (1993). The first resonant frequency (f1 or the torsional resonant frequency) could be a result of out-of-phase tangential vibration around the core axis in the upper and the lower part (Chen and De Baerdemaeker, 1993). Whereas spherical modes of vibration would be characterized by the second and third resonant frequencies (f2 and f3)