Acoustic testing of avocado for fruit ripeness evaluation

An acoustic method for nondestructive testing of avocado fruits was developed in order to determine the fruits’ firmness index, internal damping and the centeroid of the frequency response. The method is based on mechanical impulse excitation and flexible piezoelectric sensors. Emphasis was made on the engineering aspects of the method. The effects of the fruits’ irregular shape on the consistency and the variability of the test results were examined. A comparison was made between the acoustic tests and destructive penetration tests during storage. The damping ratio, which indicates fruit ripeness, increased monotonically with storage time, while the resonant frequencies and the firmness index decreased with time. A correlation coefficient R = 0.659 to 0.806 was found between the acoustic parameters and the maximum penetration force. A method is suggested to construct a ripening curve of fruits according to their “biological age”.