Early detection of fungi damage in citrus using NIR spectroscopy

Early detection of defects and diseases in fruit helps to correctly classify them and make more adequate decisions about the destination of the product: internal market, export or industry. An early fungi infection detection is especially important because a few infected fruits can disseminate the infection to a whole batch, causing great economic loses and affecting to further exports. Ensure products with excellent quality and absolute absence of fungi infections is particularly important in those batches for long conservation or to be exported. The main objective of this work is to detect the fungi infections before they can be visible. Near Infrared (NIR) spectroscopy has been employed in this work, because it is a non-destructive technique and can be easily implemented on line due to the high speed and simplicity of the process. This work is focused in the early detection of Penicilliu sp and Alternaria citri in citrus. Experiments have been conduced to evaluate the evolution of the spectra along the time in fruit inoculated with the selected fungi trying to estimate the moment in which the infection is not visible but can be detected. Experiments were conducted on navelina oranges. Two spectra of each fruit were acquired, the first one corresponding to the inoculated area and the other from sound skin. The spectra of the inoculated and control oranges were measured in intervals of eight hours until the damage was visually observed. The experiments demonstrated that the best wavelength for early detection of the infection was 1050 nm. The infection was detected between 8 and 16 hours before becoming visible in the conditions of the experiment, which are much more favourable to the growth of the fungi than current, typical storage conditions in the citrus packinghouses. Therefore, this work provides good expectations of further development of automatic inspections systems for invisible defect detection and early warning of fungi infestation in citrus packinghouses.