Elsevier

Food Chemistry

Volume 282, 1 June 2019, Pages 127-133
Food Chemistry

Simultaneous direct determination of 15 glucosinolates in eight Brassica species by UHPLC-Q-Orbitrap-MS

https://doi.org/10.1016/j.foodchem.2018.12.036Get rights and content

Highlights

  • Glucosinolates (GLS) in Brassica species were quantified by HR-HPLC-Q-Orbitrap-MS.

  • GLS profiling was performed for eight Brassica species.

  • The highest total GLS content were observed in cabbage samples.

  • The content of minor GLS helped in categorization of Brassica species.

Abstract

Glucosinolates (GLS) have been reported to have significant anti-oxidative, antimicrobial, and anti-cancer activities. The current study was aimed to develop an analytical method for glucosinolate quantitation in eight Brassica species from Gwangju, Republic of Korea. For this purpose the UHPLC-Q-Orbitrap-MS technique was used and validated for optimal extraction conditions, detection and quantitation limits, linearity, precision, and accuracy. According to the results of GLS profiling, the total GLS concentration decreased in the order of cabbage > broccoli > cauliflower > mustard > kimchi cabbage > young radish ∼ kale. All Brassica species contained glucoerucin (GER) and glucobrassicin (GBR) as major GLS with the high levels in cabbage (5.913 μM/g) and broccoli (1.723 μM/g), respectively. The contents of minor GLS were species-dependent, and could therefore be used for Brassica species classification.

Introduction

Vegetables of genus Brassica (e.g., cabbage, kale, cauliflower, broccoli, and mustard) are rich in health-promoting compounds such as soluble fiber, ascorbic acid, and glucosinolates (GLS), and are therefore classified as health foods. In particular, GLS and their derivatives are the main contributors to bitter food taste (Williams et al., 2013, Park et al., 2014) and have been intensively studied in the past several decades for their anti-oxidative, anti-fungal, anti-bacterial, and anti-cancer activities (Fahey et al., 2001, Traka and Mithen, 2009). According to the type of amino acid–derived side chain, GLS (>200 reported to date) can be divided into aliphatic, indolic, and aromatic ones (Sønderby et al., 2010, Clarke, 2010, Giamoustaris and Mithen, 1996), and their content in Brassica species depend on their growth stage and genotype (Bhandari, Jo, & Lee, 2015).

Among the large number of recent studies on the biological activity of GLS, most have been focused on the anti-cancer and fungicidal effects of several GLS breakdown products (Song and Thornalley, 2007, Conaway et al., 2002, McNaughton and Marks, 2003, Popova and Morra, 2014, Gupta et al., 2014, Wagner et al., 2013, Hanschen et al., 2014). Moreover, the European Food Safety Authority suggested that the intake of GLS with food enhances the efficiency of body defense and immune systems (Ares, Valverde, Nozal, Bernal, & Bernal, 2016). When the cells of Brassica species are disrupted by chewing or cutting, the contained GLS hydrolyze by myrosinase, an endogenous enzyme that is physically separated from GLS in intact cells by cell walls. This hydrolysis reaction furnishes bioactive breakdown products with therapeutic potential such as isothiocyanates, thiocyanates, nitriles, or indoles. Additionally, GLS in ingested food can be degraded to isothiocyanates by intestinal microorganisms (Shapiro, Fahey, Wade, Stephenson, & Talalay, 2001).

GLS can be extracted from Brassica species with methanol under water/ultrasonic bath conditions. Once extracted, GLS are separated using reverse-phase high-performance liquid chromatography and detected/quantified by UV absorption spectroscopy or mass spectrometry (Matthäus and Luftmann, 2000, Francisco et al., 2009, Ares et al., 2014, Crocoll et al., 2017). Also, some of quantitative analysis was accomplished using each GLS response factors (Brown et al., 2003, Toledo-Martín et al., 2017). However, despite the high number of available analytical procedures, data on the corresponding validation results and matrices do not exist extensively. Keeping in view this knowledge gap, the current study aimed to validate an analytical method for the simultaneous direct quantification of 15 GLS by UHPLC-Q-Orbitrap-MS; identify the difference in responsiveness of each GLS compounds; obtain and compare the GLS profiles of eight Brassica species; broccoli, cabbage, cauliflower, kale, mustard, kimchi cabbage, radish, young radish leaf, and young radish root, and identify the similar species based on GLS contents.

Section snippets

Reagents and instrumentation

The UPLC-HESI-MS system comprised of Dionex Ultimate 3000 UHPLC module and a heated electrospray ionization (HESI) quadrupole Orbitrap mass spectrometer (Thermo Scientific, Bremen, Germany) controlled by Xactive Tune 1.1 and Xcalibur 2.2 software (Thermo Fisher Scientific, San Jose, USA).

All GLS standards, namely glucoiberin (GIB), glucoraphanin (GRA), glucoerucin (GER), glucocheirolin (GOC), glucoberteroin (GOB), progoitrin (PRO), sinigrin (SIN), gluconapin (GNA), glucobrassicanapin (GBN),

Results and discussion

The quality assurance parameters of the instrument for GLS determination and the spike recovery (%) data for 15 GLS are listed in Table 2, Table 3, respectively. Table 4 summarizes the average and minimum – maximum concentrations values of the analyzed GLS reported on dry weight basis. Fig. 1 presents the calibration curves obtained for 15 GLS, and Fig. 2 presents the LDA plot for GLS concentrations in Brassica species.

Conclusions

In this study, a method for the simultaneous identification and quantitation of 15 GLS in eight Brassica species by UHPLC-Q-Orbitrap-MS was developed, optimized, and validated. Optimization of analytical conditions such as the extraction method and dilution factor confirmed that each standard compound was characterized by a different detection sensitivity, which implied that reliable quantitative analysis requires the signal intensities of standard compounds to be compared with those of

Declaration of interest statement

The authors declare no conflict of interest.

Acknowledgements

This research was supported by a grant from the World Institute of Kimchi (KE1803-3) funded by the Ministry of Science and ICT, Republic of Korea.

Conflict of interest

The authors declare no conflict of interest.

References (34)

  • I.E. Sønderby et al.

    Biosynthesis of glucosinolates – Gene discovery and beyond

    Trends in Plant Science

    (2010)
  • K. Sasaki et al.

    Quantitative profiling of glucosinolates by LC–MS analysis reveals several cultivars of cabbage and kale as promising sources of sulforaphane

    Journal of Chromatography B

    (2012)
  • L. Song et al.

    Effect of storage, processing and cooking on glucosinolate content of Brassica vegetables

    Food and Chemical Toxicology

    (2007)
  • Q.V. Vo et al.

    Synthesis and anti-inflammatory activity of aromatic glucosinolates

    Bioorganic & Medicinal Chemistry

    (2013)
  • D.J. Williams et al.

    An unusual combination in papaya (Carica papaya): The good (glucosinolates) and the bad (cyanogenic glycosides)

    Journal of Food Composition and Analysis

    (2013)
  • J. Barillari et al.

    Direct antioxidant activity of purified glucoerucin, the dietary secondary metabolite contained in rocket (Eruca sativa Mill.) seeds and sprouts

    Journal of Agricultural and Food Chemistry

    (2005)
  • S.R. Bhandari et al.

    Comparison of glucosinolate profiles in different tissues of nine Brassica crops

    Molecules

    (2015)
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    Both authors contributed equally to this paper.

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