Variation in Mineral Composition Among Species of Brassica Crops

The Brassica genus is a diverse group of plant species that include popular vegetables such as broccoli, cabbage, and kale, which are excellent sources of various essential minerals. Although considered nutritious vegetables, the mineral composition of Brassica vegetables has only been reported for a few crops. The variation in nine essential minerals was analyzed in commonly consumed portions of 31 total cultivars of 13 different vegetable crops (bok choy, broccoli, Brussels sprouts, cabbage, cauliflower, Chinese broccoli, collard greens, kale, kohlrabi, komatsuna, mustard greens, savoy cabbage, turnip, and turnip greens) from five Brassica species grown in 2012. Additionally, the year-associated environmental effect on mineral concentration was investigated for a subset of selected crop accessions grown in 2012 and regrown in 2013 (14 cultivars of seven different vegetable crops including bok choy, broccoli, cabbage, cauliflower, collard greens, kale, and savoy cabbage). All plants were grown in Urbana, Illinois with using commercial agricultural production practices. In the 2012 study, bok choy was the highest in P, Fe, Cu, and Zn. The concentrations of Mg and Na were the highest in kale. Collard greens, mustard greens, and turnip greens contained the highest levels of K, Ca, and Mn, respectively. In the two-year study with selected accessions, the mineral variation between different species was significant for all minerals except for Cu and accounted for 1-38% of the total variance. The mineral concentrations significantly differed between two growing seasons, except for macro minerals Ca, K, and Na with year effect accounting for 2-57% of the total variance. A significant interaction between species and year was also found for all minerals except for Ca, K, and Na. In this two-year study, bok choy was the highest in K, P, Fe, Zn, and Mn while Na and Cu were the highest in cauliflower. Collard greens and kale contained the highest level of Ca and Mg, respectively. In the two-year study, Ca, Mg, and Mn concentrations were negatively correlated with growing degree days, total evaporation, and total solar radiation and positively correlated with the difference between precipitation and evaporation, indicating that uptake and accumulation of these minerals might be more sensitive to environmental conditions compared to the other minerals analyzed in this study. The result of this study shows the variation in mineral composition in various Brassica crops and will help to develop breeding strategies and fertilization regimes to enhance mineral nutrients concentrations from consumption of these crops.