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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.

A non-destructive ultrasonic method was evaluated for the determination of avocado (Persea americana Mill.) maturity. Fruit of`Ettinger' and`Fuerte' avocado cultivars were sampled from tagged trees in the orchard throughout the fruiting season on six and five dates, respectively. Each fruit was subjected to ultrasonic measurements in which ultrasonic mechanical waves were excited in the avocado flesh, enabling the attenuation of waves to be calculated. The dry weight (DW) content of fruit was assessed for the determination of avocado maturity. The changes in attenuation of the ultrasonic signal and those in DW content, during the fruiting season, were functions of time in opposite tendencies: a monotonic decrease in attenuation and a monotonic increase in the DW content. The two cultivars yielded similar tendencies for attenuation and DW content. The relationship between attenuation and DW content suggested that the degree of avocado maturity can be determined by ultrasonic non-destructive technology. #