Distribution of Glucosinolates in Brassica oleracea cultivars

Abstract

Glucosinolates are important secondary compounds, commonly found in Brassicaceae. To what extent these sulfur and nitrogen containing compounds contribute to the total sulfur pool was investigated. In various cultivars of Brassica oleracea viz. curly kale, pointed cabbage, red cabbage, savoy cabbage and white cabbage, total glucosinolate content and composition of the glucosinolate pool (aliphatic, aromatic and indolyl glucosinolates) were measured, together with determination of the total and inorganic sulfur and nitrogen contents. Differences in the contents of the individual glucosinolates were found between cultivars and plant parts. In all cultivars the total glucosinolate content was highest in the roots. Roots of curly kale had the highest gluconasturtiin content (12.6 mumol g(-1) DW), while the shoot of white cabbage had the lowest glucoiberin content (0.3 mumol g(-1) DW). Between all cultivars significant differences in glucosinolate content per class were found. Aromatic glucosinolates were highest in the roots of curly kale, accounting for 63% of the total content, while the roots of savoy cabbage had the highest aliphatic glucosinolate content (8.1 mumol g(-1) DW). Expression of the total glucosinolate fraction on a total sulfur basis showed that the contribution of the glucosinolate fraction was very low (1-2%). Since a large amount of total sulfur was present as sulfate (70-88%). total glucosinolate content was also expressed on an organic sulfur basis. These values ranged between 10-23%, for white cabbage and savoy cabbage, respectively. We conclude that expression on an organic sulfur basis is a better parameter to assess the fraction of glucosinolates than on a total sulfur basis. In addition, the organic fraction appears to be a better parameter to define the sulfur requirement for structural growth