Firmness measurement of muskmelons by acoustic impulse transmission
1994
Sugiyama, J. | Otobe, K. | Hayashi, S. | Usui, S.
The acoustic impulse response of muskmelons was studied in order to evaluate their quality. Initially, the linearity and effects of sample holding conditions on the acoustic signals were demonstrated. Secondly, acoustic signals were obtained at points which divide the equator of the sample into 24 equal parts. These signals were described in a three-dimensional diagram with the axes of time, location and sound intensity, and in a two-dimensional map with gradations of 257 colors. For more complete visual comprehension, an animation display which shows the time changes of the distribution of sound intensity was presented. As a result of these analyses, it became evident that the impulse waveform of acoustic signals induced by impact was transmitted along the equator with uniform velocity. This transmission velocity became lower as the muskmelon ripened. The lower transmission velocity in the time domain agreed with the lower peak frequency in the frequency domain, both theoretically and practically. An instrument to easily measure the transmission velocity was also developed. The relationship between transmission velocity and firmness of flesh of 36 muskmelons was examined with the developed instrument. The correlation coefficient between them was 0.832. The transmission velocity of edible muskmelons ranged from 37 to 50 ml s.
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