Nutraceutical value of woad (Isatis tinctoria) flower buds of ecotypes from Sicily, Italy

Woad (Isatis tinctoria L.) is a wild plant widely diffused throughout Europe, Italy included. In ancient times it was exploited as a dye-plant, to obtain the indigo colour. Recently woad was rediscovered also for its cosmetic and anti-inflammatory properties. Belonging to Brassicaceae family, woad contains glucosinolates, which are precursor of isothiocyanates, which possess chemopreventive antioxidant properties. Although woad is not considered as an edible vegetable worldwide, rural people living around Mount Etna in Sicily, Italy, are accustomed to collect the flower buds from wild plants in the late winter, to be consumed after boiling as ingredients for salads or omelets. To investigate the nutraceutical value of woad, fresh flower buds were collected on Mount Etna slopes in Sicily over two years and analysed for their bioactive compound content. Woad samples contained considerable amounts of glucosinolates, ranging from 80 up to over 100 μmol/g d.w., which are values higher than those found in other Brassica vegetables. Only gluconapin and the most interesting glucobrassicin, which is the natural precursor of indole-3-carbinol, a multiple antitumorigenic compound, were found. High mean values were also recorded for total polyphenols and flavonoids (25 GAE mg/g d.w. and 7 CE mg/g d.w., respectively). Consequently, also the antioxidant activity (H-ORAC) of the woad flower buds resulted among the highest reported for other Brassica vegetables, being about 300 μmol TE/g d.w. Since processing can partly reduce the glucosinolate content of vegetables, different cooking ways, such as boiling and microwaving, were compared. Boiling for 10 min caused losses of 34% of total glucosinolates, while microwaving (10 min, 800 W) only reduced the glucosinolate amount by 3%. The results obtained suggest that woad flower buds could be considered as a functional food with possible chemopreventive properties.