Melon Ripeness Detection using Non-Destructive Acoustic Impulse Response

An experimental system based on acoustic technology was set up to nondestructively determine the ripeness of two export melon varieties (Zard-Eyvanekey, Sousky-Sabz). The system comprised a mechanical impulse device, sound sensor (sound level meter), recording signal equipment and the melon patch. Fruit was excited by the pendulum and the response signal was detected by non-contact sensing and processed. TSS, moisture content, acoustic and sensory levels were measured at five stages of ripening. Results indicated that, as ripening progressed, sound pressure, mass and TSS increased while resonance frequency and elastic modulus decreased for both varieties. The resonance frequency for Zard-Eyvanekey decreased from 132.25 to 111.33 Hz and for Sousky-Sabz from 128.91 to 111.33 Hz. Sound pressure increased from 49.21 to 57.74 dB for Zard-Eyvanekey and from 49.66 to 58.22 dB for Sousky-Sabz. A sensory evaluation test determined that the period of optimum ripeness of Zard Eyvanekey was at 113.34 Hz and 56.93 dB and for Sousky-Sabz was at 114.26 Hz and 56.25 dB. Changes in resonance frequency and sound pressure were slight and similar for both varieties. These results can be useful for the design of nondestructive sound systems to detect melon ripeness.