Ripening of avocado fruits studied by spectroscopic techniques.

Avocados are considered very healthy due to the high content mono-unsaturated lipid, essential vitamins and minerals, minimal sugar and no cholesterol and are therefore sometimes referred to as "the perfect fruits". Avocados, mainly grown in Latin-America, are harvested unripe and sent overseas. However, the ripening process is very difficult to assess visually and tactilely. A tool for precise noninvasive judgment of the status would be valuable as the fruit is too expensive to be cut open unripe or overdue. A white-light source and a light-emitting diode unit with four excitation wavelengths (365, 385, 395, and 405 nm) were used for reflectance and fluorescence spectroscopy in a fiber-coupled set-up for noninvasive monitoring. Twelve non-ripe avocados, with approximately the same size and appearance, were studied and divided into three groups and kept at three different storage conditions; at room temperature, in a refrigerator and a combination of the two. We showed that fluorescence was useful for following the ripening process. A method, which compensates for the spatial variations in spectral properties around a fruit, is described. Remote fluorescence monitoring, intended for orchard use, was also demonstrated. A low-cost device based on fluorescence for avocado ripeness assessment is proposed.