Flitsanov, U., Faculty of Agricultural Engineering, Technion-Israel Inst. Tech., Haifa 32000, Israel
Mizrach, A., Institute of Agricultural Engineering, Agricultural Research Organization (ARO), Volcani Center, PO Box 6, Bet Dagan 50250, Israel
Liberzon, A., Faculty of Agricultural Engineering, Technion-Israel Inst. Tech., Haifa 32000, Israel
Akerman, M., Institute for Technology and Storage of Agricultural Products, ARO, Volcani Center, PO Box 6, Bet Dagan 50250, Israel
Zauberman, G., Institute for Technology and Storage of Agricultural Products, ARO, Volcani Center, PO Box 6, Bet Dagan 50250, Israel

The low-temperature storage of avocado affects its subsequent softening process and shelf life. One of the main indices of ripeness in avocado fruit is firmness, which changes during the ripening and softening process. The temperature and duration of storage fundamentally influence the firmness of the stored fruit, and monitoring the softening of fruit enables us to regulate its shelf life. The objective of the present study was to use nondestructive ultrasonic tests to elucidate the influences of storage temperature and time on the softening process of avocado fruit. The attenuation of the ultrasonic waves transmitted through the fruit tissue changes as the fruit passes through the various softening stages during and after low-temperature storage. Four groups of avocados, each stored at a different low temperature, and a control group which was stored at room temperature (20°C) were examined during and after their designated storage times, until they reached full ripeness at room temperature. Nondestructive ultrasonic tests and destructive penetration measurements were carried out in order to determine the attenuation and the tissue firmness, respectively, of the avocados. Statistical analysis showed quite good correlation between the firmness and the ultrasonic attenuation, and their dependence on previous storage time-temperature history. This suggests that the ultrasonic measurements could be used as a nondestructive method of monitoring avocado ripeness during low-temperature storage. (C) 2000 Elsevier Science B.V.