Determination of apple firmness by nondestructive ultrasonic measurement

One of the most important quality indicators for fruit is firmness, which is highly correlated with maturity and storage time. This study was conducted to evaluate the potential use of ultrasonic parameters for the determination of apple firmness. The ultrasonic transmission system consisted of an ultrasonic pulser, two ultrasonic transmitting and receiving transducers specially fabricated for fruit, a digital oscilloscope and personal computer. For firmness of apples, apparent elastic modulus and rupture point were measured from force-deformation curves obtained by a compression test apparatus. Ultrasonic parameters such as ultrasonic velocity, and attenuation were analyzed according to the storage time of the fruit. Correlation analyses among ultrasonic parameters and fruit firmness were performed. A multiple linear regression model describing the relationship between firmness and ultrasonic parameters is proposed. The calibration equations for measurement of apple firmness were developed and validated.