Effect of Temperature and Light Exposure on the Detection of Total Intact Glucosinolate Content by LC-ESI-MS in Broccoli
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Effect of Temperature and Light Exposure on the Detection of Total Intact Glucosinolate Content by LC-ESI-MS in Broccoli Leaves Ana M. Ares & María J. Nozal & José L. Bernal & José Bernal
Received: 29 November 2013 / Accepted: 20 January 2014 # Springer Science+Business Media New York 2014
Abstract Total intact glucosinolate content in broccoli leaf extracts (Ramoso calabrese cultivar) has been determined by liquid chromatography coupled to tandem mass spectrometry with the aim of detecting potential differences in this value due to the effects of the drying temperature or the working and storage conditions (temperature and light exposure). Those broccoli leaf extracts were obtained with two different sample treatments based on heating the sample (microwave or oven), and using boiling water as extraction solvent. Significant differences were observed in the total intact glucosinolate content depending on the drying temperature and light exposure under typical working conditions. Meanwhile, those differences were less remarkable when the extracts were stored at low temperature and protected from light exposure. Keywords Intact glucosinolates . Broccoli leaves . LC-ESI-MS . Light exposure . Temperature Abbreviations ALY Glucoalyssin DW Dry weight ESI Electrospray ionization BC Glucobrassicin GER Glucoerucin GIB Glucoiberin GLSs Glucosinolates GRA Glucoraphanin GST Gluconasturtiin 4ME 4-Methoxyglucobrassicin MW Microwave A. M. Ares : M. J. Nozal : J. L. Bernal : J. Bernal (*) IU CINQUIMA, Analytical Chemistry Group, University of Valladolid, 47011 Valladolid, Spain e-mail: [email protected]
NEO 4OH SIN
Neoglucobrassicin 4-Hydroxyglucobrassicin Sinigrin
Introduction Broccoli (Brassica oleracea L. var. Italica) is a good source of many health promoting compounds and potentially protective phytochemicals including lipids, proteins, amino acids, phenolics, carotenoids, selenium, vitamins or glucosinolates (GLSs, Ares et al. 2013). GLSs are β-thioglucoside N-hydroxysulfates, with a side chain derived from amino acids and a sulfur-linked β-D-glucopyranose moiety (see Fig. 1). GLSs and/or their breakdown products (isothiocyanates) have long been known for their fungicidal, bactericidal, nematocidal and allelopathic properties, and they have recently gained research interest because of their anticancer activity (Ares et al. 2013; Moreno et al. 2006). Those compounds are present in all broccoli parts, including leaves (Ares et al. 2013, 2014; Domínguez-Perles et al. 2010; Hennig et al. 2012; Sasaki et al. 2012), which economic value could be increased, as leaves could be used as a GLSs source, and at the same time, the environmental impact would be reduced because these by-products have been usually discarded. GLSs are usually determined according to the presence (intact or non-intact desulfo-derivatives) of a sulfate group, and in most cases, the sample treatments include heating, which is required to deactivate the myrosinase enzyme and obtain a better extraction of intact GLSs (Domínguez-Perles et al. 2011). As can
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