Nondestructive firmness prediction of apple fruit using acoustic vibration response

• Published in: Scientia horticulturae 2020-02, Vol.262, p.109073, Article 109073
• Main Authors: Fathizadeh, Zahed, Aboonajmi, Mohammad, Beygi, Seyed Reza Hassan
• Format: Article
• Language: English
• Subjects: Acoustic firmness; Firmness index; Gala applee; Nondestructive test; Shelf life
• ISSN: 0304-4238; 1879-1018
• DOI: 10.1016/j.scienta.2019.109073

•The firmness of apple Gala cultivar during storage at different temperature was investigated using acoustic and vibration response.•Four new combined firmness indices Fsum, Fdif, FIsum, FIdif were introduced based on dominant frequencies to determine apple firmness.•The two indices FIsum and FIdif had the highest correlation with the reference index (puncture firmness) for the samples kept at 20 °C. In this research, firmness of Royal Gala cultivar apples during shelf life storage period was measured using acoustic vibration response method. Newly-picked apples were kept in two conditions of temperature and humidity (0 °C, 95 % and 20 °C, 40 % relative humidity). Ten apples from each group were tested every week during storage. Meanwhile, the volume, mass, density and the elasticity modulus of apples were calculated. Tests of acoustic vibration response firmness, puncture firmness and pressure were performed on each sample. The acoustic test was conducted as a nondestructive test with two sensors including a microphone to receive sound signals and a contact accelerometer to receive vibration signals. The puncture test was used as a reference evaluation. The dominant frequencies of sound (FS) and vibration (FV) were obtained and firmness indices (FIS, FIV) were calculated using the formula FI = f2 m2/3. Four new indices Fsum, Fdif, FIsum and FIdif were also calculated. Correlation coefficients of all those for indices were calculated for both groups with the puncture firmness (PF). The highest correlation in the first group belonged to FIS, FIV (98.57 %, 97.40 %) and in the second group belonged to FIsum, FIdif (96.78 %, 96.71 %). Results showed that these new indices were good indicators for determining of apple firmness. Furthermore, results revealed that acoustic vibration response is a promising technique as an inexpensive and fast way for apple texture measurement.