The IC50 values of the samples ranged between 0.32 and 0.44mg DM/mg DPPH at the beginning of storage (Table 3). UV treatment slightly reduced (~10% reduction) antioxidant activity of the samples, however, no major difference was observed between heads period due to degradation reactions. raised under 2.2 kJ or 8.8 kJ/m2 UV. Growth under 16.4 kJ/m2 UV radiation caused a 5% decrease in the antioxidant activity. This slight reduction of antioxidant activity can be associated with the reactive oxygen species (ROS) in the samples due to stress caused by UV radiation. Although the amount of antioxidant compounds, such as phenolics and flavonoids, increased following UV treatment, the ROS produced by UV radiation might nullify their positive influence on the antioxidant activity. Zlatev et al. (2012) have stated that UV-B radiation produces reactive oxygen species which cause oxidative damage in plant cells. The higher antioxidant activity, and thereby lower IC50 value, was estimated for the initial samples just after harvest. Although the antioxidant activity of the samples decreased about 30% in 15 days of storage, no further change was observed between 15 and 60 days of storage period.