Influence of pigment composition on skin color in a wide range of fruit and vegetables

The color of fruits and vegetables results from the presence of chlorophyll, carotenoid, and anthocyanin pigments. Instrumental measurements of color are used routinely in describing processes of changing color, such as fruit ripening. The applicability of using skin color measurements to predict changes in pigment composition was investigated using a wide range of fruit and vegetables. Skin color was measured using a Hunter Colorlab and represented as the coordinates X, Y, Z, L*, a*, b*, chroma (C*), and hue angle (h degrees). Identical skin samples were extracted and analyzed for chlorophyll, carotenoid, and anthocyanin concentration. Sets of pairwise scatter plots were generated for each set of color variables and for the chlorophyll, anthocyanin, and carotenoid pigments. There were linear relationships between h degrees and anthocyanin concentration and between L* and log [chlorophyll concentration]. Multiple regressions for each pigment variable and sets of color variables also were calculated. However, there was no unique linear combination of pigments that gave rise to a unique point in the color space. Conversely, a given set of coordinates in the color space can be accounted for by many combinations of pigments. Therefore, a given color measurement cannot be described in terms of a unique combination of pigments. Caution is urged in interpreting tristimulus color coordinates in terms of a simple change in pigment composition without prior knowledge of the pigment composition within the fruits and vegetables. The surface topography of fruits and vegetables may be of considerable significance in measuring color.