| Abstract: | In the Iberian Peninsula, Brassica crops are grown throughout the year and may be consumed at immature stages or leaves may be harvested by ‘picking-over’ during plant growth. Consumption of Brassicas in Portugal is high but there is no information on the levels of glucosinolates in such material. Changes in the total and individual glucosinolate concentrations of four Brassica oleracea types (two cultivars of Portuguese cabbage, one Portuguese kale type and one hybrid white cabbage) and one Portuguese Brassica napus type were monitored throughout two growing seasons, spring/summer (SS) and summer/winter (SW). Glucosinolates were determined between sowing and maturity corresponding to nine sampling dates in the leaves and five harvests in the heads. The main glucosinolates in B oleracea types were 3-methylsulphinylpropyl-, allyl- and indol-3-ylmethyl- whereas in the B napus type pent-4-enyl-, 2-hydroxybut-3-enyl- and but-3-enylglucosinolate predominated. In the leaves of B oleracea types, the highest concentration of total glucosinolates and of most of the individual glucosinolates was observed at 14 days after sowing whilst, in the heads the highest levels were noted at the start of head formation. In the B napus , the highest total and individual glucosinolate concentration was generally observed at the end of the growing season. Both for the total and for the main individual glucosinolates there were significant differences ( P< 0·001) between the nine harvest dates and between growing seasons. Between the two seasons, the glucosinolate levels in SS were generally higher than in SW. A comparison of cultivars showed the hybrid cabbage to have generally higher glucosinolate levels than the Portuguese types, except for B napus . |
