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Differing mechanisms of simple nitrile formation on glucosinolate degradation in Lepidium sativum and Nasturtium officinale seeds.

Williams, D.J. and Critchley, C. and Pun, S. and Chaliha, M. and O'Hare, T.J. (2009) Differing mechanisms of simple nitrile formation on glucosinolate degradation in Lepidium sativum and Nasturtium officinale seeds. Phytochemistry, 70 (11-12). pp. 1401-1409.

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Article Link(s): http://dx.doi.org/10.1016/j.phytochem.2009.07.035

Publisher URL: http://www.elsevier.com

Abstract

Glucosinolates are sulphur-containing glycosides found in brassicaceous plants that can be hydrolysed enzymatically by plant myrosinase or non-enzymatically to form primarily isothiocyanates and/or simple nitriles. From a human health perspective, isothiocyanates are quite important because they are major inducers of carcinogen-detoxifying enzymes. Two of the most potent inducers are benzyl isothiocyanate (BITC) present in garden cress (Lepidium sativum), and phenylethyl isothiocyanate (PEITC) present in watercress (Nasturtium officinale). Previous studies on these salad crops have indicated that significant amounts of simple nitriles are produced at the expense of the isothiocyanates. These studies also suggested that nitrile formation may occur by different pathways: (1) under the control of specifier protein in garden cress and (2) by an unspecified, non-enzymatic path in watercress. In an effort to understand more about the mechanisms involved in simple nitrile formation in these species, we analysed their seeds for specifier protein and myrosinase activities, endogenous iron content and glucosinolate degradation products after addition of different iron species, specific chelators and various heat treatments. We confirmed that simple nitrile formation was predominantly under specifier protein control (thiocyanate-forming protein) in garden cress seeds. Limited thermal degradation of the major glucosinolate, glucotropaeolin (benzyl glucosinolate), occurred when seed material was heated to >120 degrees C. In the watercress seeds, however, we show for the first time that gluconasturtiin (phenylethyl glucosinolate) undergoes a non-enzymatic, iron-dependent degradation to a simple nitrile. On heating the seeds to 120 degrees C or greater, thermal degradation of this heat-labile glucosinolate increased simple nitrile levels many fold.

Item Type:Article
Additional Information:© Crown copyright. © Elsevier Ltd.
Keywords:Glucotropaeolin; gluconasturtiin; garden cress; Lepidium sativum; watercress; nasturtium officinale; enzymatic and non-enzymatic simple nitrile formation; thiocyanate-forming protein; epithiospecifier protein; myrosinase; total and ferrous iron; cruciferous vegetables.
Subjects:Science > Biology > Biochemistry
Plant culture > Seeds. Seed technology
Plant culture > Vegetables
Plant culture > Field crops > Other field crops
Deposited On:05 Mar 2010 03:18
Last Modified:17 Mar 2011 00:53

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