Tomatoes (Lycopersicum esculentum, Mill. cv. Capita F1) were harvested at different ripening stages. Spectral images from 400 to 700 nm with a resolution of 1 nm were recorded. After recording, samples were taken from the fruit wall and the lycopene, lutein, -carotene, chlorophyll-a and chlorophyll-b concentrations were measured using HPLC. The relation between the compound concentrations measured with HPLC and the spectral images was analyzed using partial least squares (PLS) regression. The Q2 error of the predicted lycopene concentration, determined from the PLS procedure, was 0.95 on a pixel basis, and 0.96 on a tomato basis. The Q2 error of the other compounds varied from 0.73 to 0.84. Pixel-based regression made it possible to construct concentration images of the tomatoes, which showed non-uniform ripening. The method can be applied in a conveyor belt system using sorting criteria such as concentration of the compounds and the uniformity of the distribution of the concentrations.
- least-squares regression
- antioxidant activity