Significance of N, S and Se supply for the quality of Chinese Brassica-type vegetables with special reference to glucosinolates and selenium

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Cabbage vegetable (genus Brassica), which are partly consumed fresh (cooked), partly after processing using traditional or modern procedures, represent an important part of the Chinese diet. In the passed decades production was intensified using mineral fertilizers and plant protection agents as well as modern varieties. However, the effects of these measures on the contents of bioactive substances, of which the glucosinolates (mustard oil glycosides) are particular important, are not properly documented. Their content shows a differentiated response to the S status and an interaction to the N supply due to the presence of sulfone groups and the origin from S-containing amino acids (in particular alkyl and alkenylglucosinolate). The conversion products (isothiocyanates, thiocyanates and indoles) are not only responsible for the typical taste, but possess also anti-carcinogenic, anti-microbial and cholesterol-reducing effect. It is planned to set-up an extensive field experiment in Zhejiang province using Brassica campestris L. ssp. chinensis (Pak Choi) and Brassica juncea (leaf mustard). Apart from the determination of agronomical parameters the content of glucosinolates is determined, as well as the suitability of different diagnostic tools to optimise the N and S requirement. In addition the material is subjected to a traditional (Chinese) and modern preservation technique. In the material obtained in these ways the contents of quality-related constituents including glucosinolates and their breakdown products are examined again.