Differences in chlorophyll loss at 13°C for two broccoli (Brassica oleracea L.) cultivars associated with antioxidant enzyme activities

Two broccoli cultivars which have been previously found to have large differences in yellowing susceptibility were studied to determine if there was a relationship between antioxidant capability and chlorophyll loss at a simulated retail display temperature. Greenbelt cultivar retained a stable chlorophyll content over 4 days at 13 degrees C, while Emperor cultivar showed a constant decline in chlorophyll content. These differences were not related to differences in water loss. Superoxide dismutase (SOD) and peroxidase (POD) activities were approximately 30% higher in Greenbelt than in Emperor. The ratio of superoxide dismutase to peroxidase activity was also lower in Greenbelt. The susceptibility of Emperor to oxygen radical damage and lipid peroxidation is expected to be higher since an excessive SOD activity, with respect to POD activity, can potentially lead to enhanced hydroxyl radical formation. Catalase (CAT) activity was higher in Emperor, suggesting that catalase is not important in providing resistance to chlorophyll loss in broccoli. Water soluble, nonenzymatic antioxidant activity was similar for both cultivars. These results support the hypothesis that antioxidant protection offered by superoxide dismutase and peroxidase is important to retention of green color in broccoli.