Abstract: In a method for determining the concentration of glucoraphanin in a plant a sample of the plant is contacted by a polar uncharged organic solvent and comminuted such that glucoraphanin and plant material contained in the sample are dissolved in the solvent and, after removal of undissolved plant parts, the extract formed thereby is subjected to an UV-absorption measurement wherein for a first wavelength range of 200-270 nm, an absorption signal is recorded. A second derivative of the absorption signal is then obtained for a second wavelength range of 240-250 nm and the value of the minimum of the second derivative is determined and, based on this value, a concentration value for the glucoraphanin in the plant is established.