Seasonal variation in phytochemicals and antioxidant activities in different tissues of various Broccoli cultivars

Florets, leaves, and stems of twelve commercial broccoli cultivars grown in the spring and fall seasons at the National Institute of Horticultural and Herbal Science (NIHHS), Rural Development Administration (RDA), Suwon, South Korea were evaluated for glucosinolates, vitamin C, total phenol, and total flavonoid contents and antioxidant activity. The levels of all phytochemicals and antioxidant activity were significantly influenced by cultivar (C), plant part (P), and growing season (S). Among the glucosinolates, glucoraphanin and glucobrassicin were the major constituents. The highest total glucosinolate content was found in the florets of plants grown in both seasons. Phenols and flavonoids were highest levels in leaves, while vitamin C was highest in stems, suggesting that broccoli leaves and stems may be good sources of such phytochemicals. The levels of all phytochemicals were generally higher in florets in the spring than in the fall, but were higher in leaves and stems during the fall than the spring. Furthermore, higher cultivar-dependent and tissue-dependent variation was observed in the spring than in the fall. Total phenol content exhibited a strong positive correlation (r = 0.674**) with antioxidant activity, followed by total flavonoid content (r = 0.497**), indicating their significant contribution to total antioxidant activity. Key words: Antioxidant activity, broccoli, glucosinolate, seasonal variation, total phenol, vitamin C.