Application of near Infrared Spectroscopy to the Quality Control of Citrus Fruits and Mango

Abstract

NIR spectroscopy is a proved tool to measure the optical properties of the samples, which are related to their chemical and textural properties. This technology can be used for determining the internal and external quality of fruits. Accordingly, many studies have been reported for long time to assess the quality of different fresh fruits by using reflectance measurements acquired with visible-NIR spectroscopy. We have been working on the estimation of the quality of fruits using computer vision for more than twenty years, always focused on problems that affect the local industry. As the region of Valencia (Spain) is one of the main producers and exporters of citrus fruits worldwide, most of our research has been focused on this fruit, especially developing fast and reliable methods to detect defective fruit in quality control lines1. Nevertheless, our group have been carried out also other studies to determine the internal quality in other fruits with commercial interest for our region, such as, mangoes cv. ‘Osteen’, nectarines cv. 'Big Top' and cv. 'Magique', and persimmon cv. ‘Rojo Brillante’. Nowadays, the fruit producers demand automated systems to detect fruits with decay lesions that are not visible at early stages but that can spread the infection to other fruits during storage or shipping. In the case of citrus fruits, this is the most economically important postharvest disease of citrus worldwide. Detection of these diseases may considerably help to correctly discriminate and classify different fruit lots and take important decisions, based on fruit quality, about postharvest handling and final produce destination. However, the detection of rotten fruit in citrus packing-lines is performed manually, using the naked eye under ultraviolet (UV) light that induces visible fluorescence, what it is harmful for the workers. New automatic devices using UV or hyperspectral imaging2 are being investigated as possible alternatives to manual inspections. However, industry’s demands for innovative tools for rapid and cost-effective early detection have spurred considerable interest among researchers on the application of nearinfrared spectroscopy (NIRS) on citrus fruit quality monitoring as stated in the review carried out by Magwaza et al.3. Moreover, Spain is the main European producer of subtropical fruits and in particular the southwest region has a large potential for the production of Mango fruit. In the past, external quality, related to the skin colour, fruit size and shape, free from defects and the absence of decay were the most common quality determinants, but nowadays other organoleptic characteristics related to the internal quality play an important role in the consumer’s decision. Hence, another aim was to investigate the potential of visible and NIR to determine the internal quality of mango cv. ‘Osteen’, the main variety of mango grown in Spain.