Eas. Rosa et al., CHANGES IN GLUCOSINOLATE CONCENTRATIONS IN BRASSICA CROPS (BRASSICA-OLERACEA AND BRASSICA-NAPUS) THROUGHOUT GROWING SEASONS, Journal of the Science of Food and Agriculture, 71(2), 1996, pp. 237-244
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 Portug
al is high but there is no information on the levels of glucosinolates
in such material. Changes in the total and individual glucosinolate c
oncentrations of four Brassica oleracea types (two cultivars of Portug
uese cabbage, one Portuguese kale type and one hybrid white cabbage) a
nd one Portuguese Brassica napus type were monitored throughout two gr
owing seasons, spring/summer (SS) and summer/winter (SW). Glucosinolat
es were determined between sowing and maturity corresponding to nine s
ampling dates in the leaves and five harvests in the heads. The main g
lucosinolates in B oleracea types were 3-methylsulphinylpropyl-, allyl
- and indol-3-ylmethyl- whereas in the B napus type pent-4-enyl-, 2-hy
droxybut-3-enyl- and but-3-enylglucosinolate predominated. In the leav
es of B oleracea types, the highest concentration of total glucosinola
tes and of most of the individual glucosinolates was observed at 14 da
ys 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 ind
ividual 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 se
asons, the glucosinolate levels in SS were generally higher than in SW
. A comparison of cultivars showed the hybrid cabbage to have generall
y higher glucosinolate levels than the Portuguese types, except for B
napus.