Calibration Tile Slightly Influences Assessment of Color Change in Pears from Green to Yellow Using the L, a, b Space

Abstract

Green pears Green 64.01 b –17.24 b 41.35 ab 112.67 a 44.81 a 78.05 ab Yellow 64.40 ab –16.02 a 40.86 b 111.43 b 43.90 b 77.91 b Color change from green to yellow is common in many ripening fruit and in senescing processes of chlorophyllous organs. As part of a study on pear ripening (Pyrus communis L. cv. Packham’s Triumph), we were looking for a method to describe the color change of the fruit skin. In the last 20 years, color changes have been quantified frequently in the L, a, b color space. Recently, McGuire (1992) summarized uses of the L, a, b scale in objective color measurement, highlighting the benefits of using polar coordinates in the a, b plane: hue angle (angle from the +a axis to the ray from the origin to the a, b point anti-clockwise) and chroma (distance from origin to the a, b point). In agreement with this author, Gnanasekharan et al. (1992) reported some positive correlations between hue angle variations of yellowing vegetables and sensory evaluation of the color. Our survey of the last decade’s publications on the yellowing of fruit and vegetative organs revealed that a range of color parameters were presented. These included: a or b values alone, a/b or (L × a)/b ratios, hue angle or chroma. The use of three distinct calibration tiles was reported: pale green (L = 66.2, a = –15.69, b = 8.44), yellow (L = 85, a = –2.0, b = 23.8), and white (L = 97.9, a = –0.49, b = 1.91), while some authors did not specify which tile they had used. The aim of the present work was to investigate whether or not these three calibration tiles would produce any significant differences in the values L, a, b, hue, and chroma. The results will provide information about their use in experiments and the possibility of comparing various authors’ results. They may also be of some importance when examining color measurements used for quality control. Green pears were harvested from an orchard on 11 days during the first 2 weeks of Mar. 1995. Color readings of the fruit were performed with a Minolta CR200 chromameter