Flavonoids and antioxidant capacity of various cabbage genotypes at juvenile stage

Ten fresh cabbage genotypes (Brassica oleracea var capitata) representing fresh-market, processing, and storage types were evaluated for total phenols, antioxidant capacity, and flavonoids at the 3-wk juvenile stage, at which time plants are uniform in size when grown under identical soil and environmental conditions. The genotypes studied, 'Bobcat', 'Fresco', 'Little Rock', 'Marvelon', 'Rinda', 'Ramada', 'Transam', 'Genesee', 'Huron,' and 'Octoking', showed significant variations in concentration of phenolic phytochemicals and antioxidant capacity. Total phenols ranged from 110.2 mg gallic acid equivalents/100 g in 'Genesee' to 153.3 mg gallic acid equivalents/100 g in 'Bobcat'. Total antioxidant capacity varied from 108.4 to 176.1 mg vitamin C equivalents/100 g, and flavonoids from nondetectable to 2.61 mg quercetin/100 g and from 1.30 to 7.03 mg kaempferol/100 g. Apigenin, luteolin, and myricetin were not detected. Five nutritional soil supplements from agricultural and food processing sources (quercetin flavonoid complex, commercial vegetable juice, crushed onion, crushed garlic, and green tea) were added to the cabbage genotype 'Rinda' once a week for 3 wk to assess their efficacy in increasing phenolic concentrations in cabbage leaves. Addition of the supplements generally resulted in increased levels of total phenols (97% with commercial vegetable juice), antioxidant capacity (41% with crushed onion), and quercetin plus kaempferol (110% with commercial vegetable juice) in the juvenile 'Rinda' plants with no significant increase with the addition of green tea. Nutritional soil supplements could provide enhanced levels of bioactive phenolic compounds as antioxidants in cabbage and therefore to consumers.