Laser diagnostic technology for early detection of pathogen infestation in orange fruits

Abstract

Due to an increased expectation of food products that respect high quality and safety standards, there is a need for the growth of accurate, fast, objective and non-destructive technologies for quality determination of food and agricultural products. For this purpose, a diagnostic system based on laser photoacoustic spectroscopy (LPAS) was developed at ENEA Frascati Molecular Spectroscopy Laboratory (Italy). In the design of the photoacoustic detector, particular emphasis was placed in attaining a high sensitivity in detecting ethylene (ET) down to sub-parts per billion level (minimum detectable concentration 0.2 ppb). This was required due to the necessity to monitor and follow up ET production at a single fruit scale. ET is normally synthesised in very low amounts by healthy citrus fruits; however stress conditions such as pathogen attack may induce a substantial increase in the synthesised ET. In the present paper, the comparison between the ET emitted by healthy oranges ( Citrus sinensis L. Osbeck) cv Navel and by Phytophthora citrophthora infested Navel orange fruits are reported. The obtained results show a well evident increase in ET emission from the infested fruit with respect to the healthy one, even 24 h after the inoculation with the pathogen; at that time the tissue necrosis was not yet visible, and the fruit was also not yet damaged. The possibility to perform a real time non-destructive detection of ET traces makes the LPAS a powerful tool for monitoring the healthy state of the citrus fruits.