Measuring color hue in 'Sunrise Solo' papaya using a flatbed scanner

Color hue is a variable frequently used postharvest to assess the physiological maturity of various fruits. In general, mean color hue is quantified by visual techniques, but this method, based on human grading, is tedious and may be erroneous. The color of fruit peel is frequently determined at four points randomly distributed on the equatorial region of a fruit, but this practice can lead to biased results because these points represent the equatorial region only and not the total area of the fruit peel. consequently, this bias is not due to equipment measurement errors, but to the bias in the sampling process of the points on the fruit epidermis. an alternative to such methods is the digital image which provides information about all regions of the fruit peel, and results in a more accurate mean hue. however, this technique requires calibration to correct the values of luminance, hue and intensity obtained through the scanner. This calibration can be performed from color patterns such that each pattern is assessed by means of a scanner and a colorimeter. Thus, an experiment was conducted using 297 color patterns based on the munssel color chart for plant tissue. The results showed that the scanner could be used as a device for color assessment where the determination coefficients were above 0.9 for all color components. Next, a second experiment was conducted in order to compare the scanner and colorimeter methodologies. For this, we used a papaya fruit, cv. Sunrise Solo, which was assessed by these two devices for a period of 19 days. The results showed that the image analysis measures have a different mean hue when compared with the mean hue obtained by the method using a colorimeter. Therefore, it is recommended that digital image analysis be used for the evaluation of the hue of fruit peel color when fruit presents non-uniform coloration.