Fresh red alimentary pigment extracted from Monascus purpureus fungus exhibits an intense EPR line consisting of a single, narrow line, attributed to a quinone radical. When irradiated with 7 MeV electrons or 6 0 Co γ-rays, the amplitude of this line increased with the absorbed dose following a saturation exponential dependency up to 10 kGy. During annealing treatment (isothermal heating at 100 o C) the irradiation centers decay exponentially with a half-life time of 2.30<space>min.