Carotenoid, Tocopherol, and Ascorbate Variability in Cruciferous Vegetables

Abstract

Antioxidants have been associated with reduced risk of cardiovascular disease and several types of cancer. Recent studies indicate that cruciferous vegetables contain high levels of these antioxidants. We assayed the edible portions of 52 broccoli and 13 cabbage, kale, cauliflower, and Brussels sprouts genotypes to determine variability of α-carotene, β-carotene, α-tocopherol, γ-tocopherol, and ascorbate within and between varieties of Brassica oleracea. Emphasis was placed on broccoli due to its economic importance and consumer preference. Samples of each genotype in replicated trials were harvested at fresh-market stage, frozen immediately in liquid nitrogen, and placed in –80 °C. HPLC with an amine column was used to measure ascorbate in fresh, frozen samples. Tissue for carotenoid and tocopherol analysis was freeze-dried prior to extraction. Carotenoid and tocopherol concentrations were simultaneously measured using a reverse-phase HPLC system developed in our laboratory. Results indicate that there is substantial variability both within and between varieties. Kale had the highest levels of these compounds, followed by broccoli and Brussels Sprouts with intermediate levels, then by cabbage and cauliflower which were relatively poor sources. Based on dry weight, broccoli heads ranged (in mg/g) from 0–2.9, 23–94, 24–222, and 2-–5 for α-carotene, β-carotene, α-tocopherol, and γ-tocopherol, respectively. The range of ascorbate was 54–120 mg/100 g fresh weight. These results contradict the general perception that all broccoli lines are equally beneficial in potential disease prevention. The information gained from this study can be used to help consumers select foods that promote a healthy lifestyle and in breeding programs to develop new germplasm that will enhance the antioxidant potential of our food supply.