Available online at www.sciencedirect.com Postharvest Biology and Technology 46 (2007) 271–274 Research Note Nondestructive ultrasonic monitoring of tomato quality during shelf-life storage Amos Mizrach ∗ Institute of Agricultural Engineering, ARO, Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel Received 23 March 2007; accepted 16 May 2007 Abstract A nondestructive ultrasonic method was used to monitor the firmness and sugar content of greenhouse tomatoes (cv. 870) during their shelf-life. This method is based on measurement of acoustic wave attenuation in the fruit tissue, by means of ultrasonic probes in contact with the fruit peel. The fruit for measurement were transferred from the greenhouse to a controlled-temperature room, and were subjected to nondestructive ultrasonic tests and also to destructive penetration measurements of firmness. The results were analyzed statistically to determine the changing relationships between the ultrasonic attenuation measurements and the destructive measurements, during the shelf-life. The differences in the acoustic signals transmitted through the tissue of fruit of various degrees of firmness were measured and analyzed as well. The measured attenuation and the firmness were found to decrease significantly during shelf-life. A linear relationship between the attenuation and the firmness was observed until the end of the softening process. This suggests that this ultrasonic method might be used as a nondestructive means of monitoring the firmness of tomatoes during various stages of storage. © 2007 Elsevier B.V. All rights reserved. Keywords: Ultrasonics; Tomato; Lycopersicon esculentum; Firmness; Sugar content; Ripeness; Nondestructive; Quality 1. Introduction Ripening indicators in greenhouse tomatoes (Lycopersicon esculentum Mill) are softening of the flesh, decreasing acid- ity, and change in color. The change in sugar content during maturation is not considerable, but is important to consumers. Tissue firmness is the property most relevant to consumer per- ceptions of ripening, and it is the factor most closely related to the stage of maturity in tomatoes (Keidar and Geisenberg, 1989). A trained person can assess this parameter, but at present a destructive measurement method is required. Consumer demand for high-quality products raises the need for a reliable, rapid, nondestructive, non-invasive technique for maturity determina- tion, especially during harvest and at the packing site. There are several techniques for nondestructive measurement of qual- ity parameters in various fruit and vegetables, e.g., acoustic impulse response (Schotte et al., 1999), and ultrasound (Mizrach et al., 1997; Verlinden et al., 2004). The ultrasonic technique was suggested previously to determine some quality parameters ∗ Tel.: +972 3 9683451; fax: +972 3 9604704. E-mail address: amos@volcani.agri.gov.il. of fruit and vegetables (e.g., Mizrach et al., 1994) but not for fresh greenhouse tomatoes. Verlinden et al. (2004) used a simi- lar ultrasonic technique to evaluate chilling injury in tomatoes, but found difficulties with contact pressure between the probes and the tomato flesh. They applied destructive penetration of the probes to record their results and suggested the development of a nondestructive ultrasonic technique to make this method applicable. A nondestructive, ultrasonic method, developed by Mizrach et al. (1994) is a potential solution; it is based on a patented sys- tem that enables the fruit quality attributes to be determined by measuring the changes in ultrasonic waves passing through the peel and flesh (Mizrach et al., 1995) with no damage to the fruit. Several models of devices based on this technique have been developed and successfully used for nondestructive determina- tion of quality attributes of mangoes (Mizrach et al., 1997), of avocados during their shelf-life (Mizrach and Flitsanov, 1999), and of the maturity of avocados while on the tree (Mizrach et al., 1999). This technique has also been successfully used to monitor the softening of avocados in low-temperature storage (Mizrach et al., 2000). A progress report summarized the research on the use of the ultrasonic technique to determine avocado and mango fruit properties (Mizrach, 2000). 0925-5214/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.postharvbio.2007.05.012