A comprehensive study on the colour of virgin olive oils and its relationship with their chlorophylls and carotenoids indexes (I): CIEXYZ non-uniform colour space

Up to 1700 samples of virgin olive oil from eight varieties at different ripening stages were analyzed for their colour, in terms of the CIEXYZ space, and pigments. The samples differed greatly in pigments contents (the chlorophylls index ranging from 0.15 to 61.96 mg/kg and the carotenoid one from 0.53 to 31.51 mg/kg) and therefore in colour, as it was inferred from the variations in X (16.19–91.39), Y (18.32–98.16), Z (0.17–81.14), purity of excitation (13.99–99.02), colorimetric purity (20.80–99.34) and dominant wavelength (566–575 nm). After exploring the relationships between the colour parameters and the indexes it was concluded that the purity of excitation and the colorimetric purity were better correlated with the carotenoid index than to the chlorophyll index and that λd was much poorly correlated to both. When multiple regression analyses were applied and the set of tristimulus values was considered altogether the best correlation was found with the carotenoid content.