Extending the Use of Ultraviolet Light for Fruit Quality Sorting in Citrus Packinghouses

Illumination with ultraviolet light (UV) is commonly used in citrus packinghouses as a means to aid in the identification and removal of decayed oranges from the packline.  This technique is effective because areas of decay strongly fluoresce under UV illumination.  It was observed that oranges often have other areas on the peel with lesser degrees of fluorescence and experiments were conducted to determine if their abundance was predictive of fruit quality after storage.  Three separate experiments were conducted using the UV room of a packinghouse where oranges were removed from the packingline and placed into different classes based upon the amount of peel fluorescence present:  class 0, having little or no fluorescence; class 1, having a limited number of small fluorescing areas; class 2, having numerous fluorescing areas; and class 3, having large fluorescing areas indicative of decay or severe mechanical injury.  The following day and again after 3 weeks at 15 °C the fruit were evaluated and separated into groups based upon peel quality and the presence of decay.  Marketable fruit were considered to be fruit that could be classified as either fancy or choice grade.  Class 3, which would be the fruit removed in the UV rooms under current practices, had high levels of decay and only 5% of the fruit could be considered as marketable after 3 weeks of storage.  Classes 0 and 1, representing fruit with no or low amounts of fluorescence, were similar in quality and had an average of 57% of the fruit being marketable after 3 weeks of storage.  Only 28% of fruit in class 2, however, were marketable after the same amount of storage, this being due to lesions on the peel and decay that occurred during storage.  Peel UV fluorescence, even at amounts below what are currently considered in commercial packinghouses, appears to be predictive of orange quality following storage.