465 Proc. 4 th . Int. Conf. On Postharvest Eds. R. Ben-Arie & S. Philosoph-Hadas Acta Hort. 553, ISHS 2001 NONDESTRUCTIVE ULTRASONIC TECHNIQUE FOR FRUIT QUALITY DETERMINATION Amos Mizrach Institute of Agricultural Engineering, A.R.O., the Volcani Center, P.O.Box 6, Bet Dagan, 50250. Israel. E-mail: amos@agri.gov.il Keywords : Ultrasonic, nondestructive testing, spectral analysis, fruits, quality. Abstract A nondestructive ultrasonic measurement system was developed for some transmission parameters which might have quantitative relations with the maturity, firmness and other quality-related properties of avocado and mango fruits. The system utilizes a set of low- frequency probes arranged to measure the ultrasonic signal transmitted and received over a short distance across the peel. The attenuation of the ultrasonic waves transmitted through the peel and the attached fruit tissue changes progressively as a result of the ripening and softening of the fruit during the growing season and in the course of storage. The present study quantitatively addresses the linkage between the ultrasonic attenuation and the physiological parameters of the flesh of the fruits. Results were obtained in the time and frequency domains, and the data set was analyzed statistically to identify the relations between the major physiological indices and the ultrasonic parameters. Quantitative relations were developed to describe the linkage between ultrasonic parameters and the maturity, firmness and other quality-related properties. 1. Introduction Maturity determination of fruits before picking, and subsequent quality evaluation are important issues. Some of the physical properties of the fruit that develop as the fruit matures, are indicative of its quality. In avocado fruits, maturity is determined by firmness oil content and dry weight (DW) measurements of the flesh, according to which the harvest date is determined (Lewis, 1978). Maturity indicators in mango are softening of the flesh, decreasing acidity and increasing contents of sugars, soluble solids and total solids. Chemical tests are an important means for determining the maturity of fruits, but firmness is the factor most closely related to the stage of maturity (Peacock et al., 1986). Penetration tests are the most accepted method for measuring firmness, but they are destructive and time-consuming. A nondestructive method for determination of avocado and mango maturity would be preferred. Mizrach et al. (1989) built and evaluated a system for determination of the basic acoustic properties of some fruits and vegetables, i.e., wave propagation velocity and attenuation, and suggested using this technique for the nondestructive quality evaluation of fruits and vegetables. In addition, strong interdependence between ultrasonic properties and post-harvest ripening parameters of the fruit tissue were derived in further studies (Mizrach et al., 1991; 1992). A device based on the use of ultrasonic waves transmitted through the peel and the flesh of a whole fruit was patented by Mizrach et al. (1994) and used in several studies. Mizrach and Flitsanov (1999) and Mizrach et al. (1996; 1997; 1999a) measured ultrasonic wave attenuation in avocado and mango fruits in the time domain, and in mango in the frequency domain (Mizrach et al., 1999b), to assess fruit properties and to relate them to shelf life. In all of these studies, the attenuation measurements, taken in the course of storage, were correlated with the results of destructive penetration measurements of firmness and of physiological tests of the fruit tissue. The present paper reviews all the studies mentioned above, the technologies,