Improvement in determination of isothiocyanates using high-temperature reversed-phase HPLC

High-level and reusable preparation of sulforaphane by yeast cells expressing myrosinase

Myrosinase is a key tool for the fast and efficient preparation of sulforaphane which is one of the prominent natural ingredients found in brassicaceous vegetables. Here, the glucoraphanin-hydrolyzing activity of a Yarrowia lipolytica 20-8 harboring myrosinase reached 73.28 U/g dry cell weight, indicating that it had a potential application in sulforaphane preparation from glucoraphanin. An efficient and reusable process for sulforaphane preparation via myrosinase produced by Y. lipolytica 20-8 was constructed. In detail, as high as 10.32 mg sulforaphane could be produced from 1 g broccoli seed under the reaction of 40 U yeast whole-cell catalyst within 15 min with the conversion efficiency of 99.86%. Moreover, when the yeast whole-cell catalyst was reused 7 and 10 times, as high as 92.53% and 87.56% of sulforaphene yield of the initial level could be retained, respectively. Therefore, this yeast whole-cell is a potent biocatalyst for the efficient and reusable preparation of sulforaphane.

Biochemical Characterization of a Novel Myrosinase Rmyr from Rahnella inusitata for High-Level Preparation of Sulforaphene and Sulforaphane

Myrosinase is a biotechnological tool for the preparation of sulforaphane and sulforaphene with a variety of excellent biological activities. In this study, a gene encoding the novel glycoside hydrolase family 3 (GH3) myrosinase Rmyr from Rahnella inusitata was heterologously expressed in Escherichia coli BL21 (DE3). The purified Rmyr shows the highest activity at 40 °C and pH 7.0; meanwhile, its half-life at 30 °C reaches 12 days, indicating its excellent stability. Its sinigrin-, glucoraphenin-, and glucoraphanin-hydrolyzing activities were 12.73, 4.81, and 6.99 U/mg, respectively. Rmyr could efficiently degrade the radish seed-derived glucoraphenin and the broccoli seed-derived glucoraphanin into sulforaphene and sulforaphane within 10 min with the highest yields of 5.07 mg/g radish seeds and 9.56 mg/g broccoli seeds, respectively. The highest conversion efficiencies of sulforaphane from glucoraphanin and sulforaphene from glucoraphenin reached up to 92.48 and 97.84%, respectively. Therefore, Rmyr is a promising and potent biocatalyst for efficient and large-scale preparation of sulforaphane and sulforaphene.

Current Methods for the Extraction and Analysis of Isothiocyanates and Indoles in Cruciferous Vegetables

Cruciferous vegetables are characterized by the presence of sulfur-containing secondary plant metabolites known as glucosinolates (GLS). The consumption of cruciferous vegetables such as broccoli, cabbage, rocket salad, and cauliflower has been related to the prevention of non-communicable diseases. Their beneficial effects are attributed to the enzymatic degradation products of GLS, e.g., isothiocyanates and indoles. Owing to these properties, there has been a shift in the last few years towards the research of these compounds and a wide range of methods for their extraction and analytical determination have been developed. The aim of this review is to present the sample preparation and extraction procedures of isothiocyanates and indoles from cruciferous vegetables and the analytical methods for their determination. The majority of the references that have been reviewed are from the last decade. Although efforts towards the application of eco-friendly non-conventional extraction methods have been made, the use of conventional solvent extraction is mainly applied. The major analytical techniques employed for the qualitative and quantitative analysis of isothiocyanates and indoles are high-performance liquid chromatography and gas chromatography coupled with or without mass spectrometry detection. Nevertheless, the analytical determination of isothiocyanates presents several problems due to their instability and the absence of chromophores, making the simultaneous determination of isothiocyanates and indoles a challenging task.

A Newly Developed HPLC-UV/Vis Method Using Chemical Derivatization with 2-Naphthalenethiol for Quantitation of Sulforaphane in Rat Plasma

Sulforaphane (SFN), a naturally occurring isothiocyanate, has received significant attention because of its ability to modulate multiple biological functions, including anti-carcinogenic properties. However, currently available analytical methods based on high-performance liquid chromatography (HPLC)-UV/Vis for the quantification of SFN have a number of limitations, e.g., low UV absorbance, sensitivity, or accuracy, due to the lack of a chromophore for spectrometric detection. Therefore, we here employed the analytical derivatization procedure using 2-naphthalenethiol (2-NT) to improve the detectability of SFN, followed by HPLC separation and quantification with UV/Vis detection. The optimal derivatization conditions were carried out with 0.3 M of 2-NT in acetonitrile with phosphate buffer (pH 7.4) by incubation at 37 °C for 60 min. Separation was performed in reverse phase mode using a Kinetex C18 column (150 mm × 4.6 mm, 5 μm) at a flow rate of 1 mL/min, with 0.1% formic acid as a mobile phase A, and acetonitrile/0.1% formic acid solution as a mobile phase B with a gradient elution, with a detection wavelength of 234 nm. The method was validated over a linear range of 10-2000 ng/mL with a correlation of determination (R2) > 0.999 using weighted linear regression analysis. The intra- and inter-assay accuracy (% of nominal value) and precision (% of relative standard deviation) were within ±10 and <15%, respectively. Moreover, the specificity, recovery, matrix effect, process efficiency, and short-term and long-term stabilities of this method were within acceptable limits. Finally, we applied this method for studying in vivo pharmacokinetics (PK) following oral administration of SFN at doses of 10 or 20 mg/kg. The Cmax (μg/mL), Tmax (hour), and AUC0-12h (μg·h/mL) of each oral dose were 0.92, 1.99, and 4.88 and 1.67, 1.00, and 9.85, respectively. Overall, the proposed analytical method proved to be reliable and applicable for quantification of SFN in biological samples.

Preparation of Sulforaphene from Radish Seed Extracts with Recombinant Food-Grade Yarrowia lipolytica Harboring High Myrosinase Activity

Sulforaphene prepared from glucoraphenin by myrosinase is one of the main active ingredients of radish, which has various biological activities and brilliant potential for food and pharmaceutical applications. In this paper, a recombinant food-grade yeast transformant 20-8 with high-level myrosinase activity was constructed by over-expressing a myrosinase gene from Arabidopsis thaliana in Yarrowia lipolytica. The highest myrosinase activity produced by the transformant 20-8 reached 44.84 U/g dry cell weight when it was cultivated in a 10 L fermentor within 108 h. Under the optimal reaction conditions, 6.1 mg of sulforaphene was yielded from 1 g of radish seeds under the catalysis of the crude myrosinase preparation (4.95 U) at room temperature within 1.5 h. What is more is that when the whole yeast cells harboring myrosinase activity were reused 10 times, the sulforaphene yield still reached 92.53% of the initial level. Therefore, this efficient approach has broad application prospects in recyclable and large-scale preparation of sulforaphene.

Relationship between mustard pungency and allyl-isothiocyanate content: A comparison of sensory and chemical evaluations

The correlation of sensory and chemically evaluated pungency of mustard products was investigated via a time-intensity (TI) study and quantification of allyl isothiocyanate (AITC) contents using high-performance liquid chromatography (HPLC). Sweet, medium hot, hot, and extra hot commercial mustard products from different brands were examined. Notably, we found significant differences (p < 0.05) between the maximum perceived pungency intensity of various mustard products. The maximum perceived intensity (I_max ), the duration of the decreasing phase (DUR_Dec ), and the area under the curve (AUC) values increased proportionally to the increase in the sample AITC content and were also higher in products classified as hot than in sweet mustards. The AITC concentration varied greatly between products from different brands and also between different sensory evaluated pungency levels. Furthermore, sensory evaluations and analytical results were correlated using regression analysis. The best correlation (correlation coefficient 0.891) was observed between the AITC concentration and AUC, when compared to that between the AITC concentration and DUR_Dec (correlation coefficient 0.856) or the I_max value (correlation coefficient 0.803). The calculated regression model indicates that a higher AITC content induces an intensified trigeminal pungency sensation and that the sensory and chemical evaluations of mustard products were positively correlated. Therefore, by using this regression model, the sensory rating of mustard products may be predicted by chemical analysis of the AITC contents. PRACTICAL APPLICATION: This research paper provides a method to quantify the pungency inducing irritant allyl isothiocyanate in commercial mustard products and demonstrates a correlation between sensory and chemical data. Therefore, the amounts of sensory tests in product quality assurance can be reduced and replaced or at least supported by chemical quantification of pungent substances (especially AITC) in mustard products.

Benzyl Isothiocyanate and Phenethyl Isothiocyanate Inhibit Adipogenesis and Hepatosteatosis in Mice with Obesity Induced by a High-Fat Diet

Benzyl isothiocyanate (BITC) and phenethyl isothiocyanate (PEITC) are organosulfur phytochemicals rich in cruciferous vegetables. We investigated the antiobesity and antihepatosteatosis activities of BITC and PEITC and the working mechanisms involved. C57BL/6J mice were fed a low-fat diet (LFD), a high-fat diet (HFD), or a HFD supplemented with 0.5 (L) or 1 g/kg (H) BITC or PEITC for 18 weeks. Compared with the HFD group, BITC or PEITC decreased the final body weight of mice in a dose-dependent manner [39.0 ± 3.1 (HFD), 34.4 ± 3.2 (BITC-L), 32.4 ± 2.8 (BITC-H), 36.2 ± 4.4 (PEITC-L), and 32.8 ± 2.9 (PEITC-H) g, p < 0.05], relative weight of epididymal fat [5.7 ± 0.4 (HFD), 4.7 ± 0.7 (BITC-L), 3.7 ± 0.3 (BITC-H), 4.4 ± 1.0 (PEITC-L), and 3.2 ± 0.6 (PEITC-H) %, p < 0.05], hepatic triglycerides [98.4 ± 6.0 (HFD), 81.0 ± 8.9 (BITC-L), 63.5 ± 5.6 (BITC-H), 69.3 ± 5.6 (PEITC-L), and 49.4 ± 2.9 (PEITC-H) mg/g, p < 0.05], and plasma total cholesterol [140 ± 21.3 (HFD), 109 ± 5.6 (BITC-L), 101 ± 11.3 (BITC-H), 126 ± 8.3 (PEITC-L), and 91.8 ± 12.7 (PEITC-H) mg/dL, p < 0.05]. Q-PCR and immunoblotting assays revealed that BITC and PEITC suppressed the expression of liver X receptor α, sterol regulatory element-binding protein 1c, stearoyl-CoA desaturase 1, fatty acid synthase, and acetyl-CoA carboxylase in both epididymal adipose and liver tissues. After a single oral administration of 85 mg/kg BITC or PEITC, the maximum plasma concentrations ( C_max) of BITC and PEITC were 5.8 ± 2.0 μg/mL and 4.3 ± 1.9 μg/mL, respectively. In 3T3-L1 adipocytes, BITC and PEITC dose-dependently reduced adipocyte differentiation and cell cycle was arrested in G0/G1 phase. These findings indicate that BITC and PEITC ameliorate HFD-induced obesity and fatty liver by down-regulating adipocyte differentiation and the expression of lipogenic transcription factors and enzymes.

Chemopreventive glucosinolate accumulation in various broccoli and collard tissues: Microfluidic-based targeted transcriptomics for by-product valorization

Floret, leaf, and root tissues were harvested from broccoli and collard cultivars and extracted to determine their glucosinolate and hydrolysis product profiles using high performance liquid chromatography and gas chromotography. Quinone reductase inducing bioactivity, an estimate of anti-cancer chemopreventive potential, of the extracts was measured using a hepa1c1c7 murine cell line. Extracts from root tissues were significantly different from other tissues and contained high levels of gluconasturtiin and glucoerucin. Targeted gene expression analysis on glucosinolate biosynthesis revealed that broccoli root tissue has elevated gene expression of AOP2 and low expression of FMOGS-OX homologs, essentially the opposite of what was observed in broccoli florets, which accumulated high levels of glucoraphanin. Broccoli floret tissue has significantly higher nitrile formation (%) and epithionitrile specifier protein gene expression than other tissues. This study provides basic information of the glucosinolate metabolome and transcriptome for various tissues of Brassica oleracea that maybe utilized as potential byproducts for the nutraceutical market.

HPLC Separation of Sulforaphane Enantiomers in Broccoli and Its Sprouts by Transformation into Diastereoisomers Using Derivatization with (S)-Leucine

Racemic sulforaphane, which was derivatized with (S)-leucine (l-leucine), was resolved by reversed phase HPLC with UV detection. The optimum mobile phase conditions were found to be 10 mM citric acid (pH 2.8) containing 22% methanol at 35 °C using detection at 254 nm. Sulforaphane enantiomers in florets and stems of five brands of broccoli and leaves and stems of three brands of broccoli sprouts were analyzed by the proposed HPLC method. Both sulforaphane enantiomers were detected in all of the samples. The S/R ratios of sulforaphane in broccoli samples were 1.5-2.6/97.4-98.5% for florets and 5.0-12.1/87.9-95.0% for stems. The S/R ratios in broccoli sprout samples were higher than those in broccoli samples and were found to be 8.3-19.7/80.3-91.7% for leaves and 37.0-41.8/58.2-63.0% for stems. (S)-Sulforaphane detected in the broccoli and its sprout samples was positively identified by separately using an HPLC with a chiral column (Chiralpak AD-RH) and mass spectrometry.

Influence of Sulforaphane Metabolites on Activities of Human Drug-Metabolizing Cytochrome P450 and Determination of Sulforaphane in Human Liver Cells

The influence of metabolites of sulforaphane, natural compounds present in broccoli (Brassica oleracea var. botrytis italica) and in other cruciferous vegetables, on drug-metabolizing cytochrome P450 (CYP) enzymes in human liver microsomes and possible entry of sulforaphane into human hepatic cells were investigated. Metabolites studied are compounds derived from sulforaphane by the mercapturic acid pathway (conjugation with glutathione and by following reactions), namely sulforaphane glutathione and sulforaphane cysteine conjugates and sulforaphane-N-acetylcysteine. Their possible effect on four drug-metabolizing CYP enzymes, CYP3A4 (midazolam 1'-hydroxylation), CYP2D6 (bufuralol 1'-hydroxylation), CYP1A2 (7-ethoxyresorufin O-deethylation), and CYP2B6 (7-ethoxy-4-(trifluoromethyl)coumarin O-deethylation), was tested. Inhibition of four prototypical CYP activities by sulforaphane metabolites was studied in pooled human liver microsomes. Sulforaphane metabolites did not considerably affect biological function of drug-metabolizing CYPs in human liver microsomes except for CYP2D6, which was found to be inhibited down to 73-78% of the original activity. Analysis of the entry of sulforaphane into human hepatocytes was done by cell disruption by sonication, methylene chloride extraction, and modified high-performance liquid chromatography method. The results have shown penetration of sulforaphane into the human hepatic cells.

Profiles of Glucosinolates, Their Hydrolysis Products, and Quinone Reductase Inducing Activity from 39 Arugula (Eruca sativa Mill.) Accessions

Glucosinolates, their hydrolysis product concentrations, and the quinone reductase (QR) inducing activity of extracts of leaf tissue were assayed from 39 arugula (Eruca sativa Mill.) accessions. Arugula accessions from Mediterranean countries (n = 16; Egypt, Greece, Italy, Libya, Spain, and Turkey) and Northern Europe (n = 2; Poland and United Kingdom) were higher in glucosinolates and their hydrolysis products, especially glucoraphanin and sulforaphane, compared to those from Asia (n = 13; China, India, and Pakistan) and Middle East Asia (n = 8; Afghanistan, Iran, and Israel). The QR inducing activity was also the highest in Mediterranean and Northern European arugula accessions, possibly due to a significant positive correlation between sulforaphane and QR inducing activity (r = 0.54). No nitrile hydrolysis products were found, suggesting very low or no epithiospecifier protein activity from these arugula accessions. Broad sense heritability (H(2)) was estimated to be 0.91-0.98 for glucoinolates, 0.55-0.83 for their hydrolysis products, and 0.90 for QR inducing activity.

The Role of Glucosinolate Hydrolysis Products from Brassica Vegetable Consumption in Inducing Antioxidant Activity and Reducing Cancer Incidence

The bioactivity of glucosinolates (GSs), and more specifically their hydrolysis products (GSHPs), has been well documented. These secondary metabolites evolved in the order Brassicales as plant defense compounds with proven ability to deter or impede the growth of several biotic challenges including insect infestation, fungal and bacterial infection, and competition from other plants. However, the bioactivity of GSHPs is not limited to activity that inhibits these kingdoms of life. Many of these compounds have been shown to have bioactivity in mammalian systems as well, with epidemiological links to cancer chemoprevention in humans supported by in vitro, in vivo, and small clinical studies. Although other chemopreventive mechanisms have been identified, the primary mechanism believed to be responsible for the observed chemoprevention from GSHPs is the induction of antioxidant enzymes, such as NAD(P)H quinone reductase (NQO1), heme oxygenase 1 (HO-1), glutamate-cysteine ligase catalytic subunit (GCLC), and glutathione S transferases (GSTs), through the Keap1-Nrf2-ARE signaling pathway. Induction of this pathway is generally associated with aliphatic isothiocyanate GSHPs, although some indole-derived GSHPs have also been associated with induction of one or more of these enzymes.

Correlation of quinone reductase activity and allyl isothiocyanate formation among different genotypes and grades of horseradish roots

Horseradish (Armoracia rusticana) is a perennial crop and its ground root tissue is used in condiments because of the pungency of the glucosinolate (GS)-hydrolysis products allyl isothiocyanate (AITC) and phenethyl isothiocyanate (PEITC) derived from sinigrin and gluconasturtiin, respectively. Horseradish roots are sold in three grades: U.S. Fancy, U.S. No. 1, and U.S. No. 2 according to the USDA standards. These grading standards are primarily based on root diameter and length. There is little information on whether root grades vary in their phytochemical content or potential health promoting properties. This study measured GS, GS-hydrolysis products, potential anticancer activity (as quinone reductase inducing activity), total phenolic content, and antioxidant activities from different grades of horseradish accessions. U.S. Fancy showed significantly higher sinigrin and AITC concentrations than U.S. No. 1 ,whereas U.S. No. 1 showed significantly higher concentrations of 1-cyano 2,3-epithiopropane, the epithionitrile hydrolysis product of sinigrin, and significantly higher total phenolic concentrations than U.S. Fancy.

The antibacterial properties of isothiocyanates

Isothiocyanates (ITCs) are natural plant products generated by the enzymic hydrolysis of glucosinolates found in Brassicaceae vegetables. These natural sulfur compounds and their dithiocarbamate conjugates have been previously evaluated for their anti-cancerous properties. Their antimicrobial properties have been previously studied as well, mainly for food preservation and plant pathogen control. Recently, several revelations concerning the mode of action of ITCs in prokaryotes have emerged. This review addresses these new studies and proposes a model to summarize the current knowledge and hypotheses for the antibacterial effect of ITCs and whether they may provide the basis for the design of novel antibiotics.

Total myrosinase activity estimates in brassica vegetable produce

Isothiocyanates, generated from the hydrolysis of glucosinolates in plants of the Brassicaceae family, promote health, including anticancer bioactivity. Hydrolysis requires the plant enzyme myrosinase, giving myrosinase a key role in health promotion by brassica vegetables. Myrosinase measurement typically involves isolating crude protein, potentially underestimating activity in whole foods. Myrosinase activity was estimated using unextracted fresh tissues of five broccoli and three kale cultivars, measuring the formation of allyl isothiocyanate (AITC) and/or glucose from exogenous sinigrin. A correlation between AITC and glucose formation was found, although activity was substantially lower measured as glucose release. Using exogenous sinigrin or endogenous glucoraphanin, concentrations of the hydrolysis products AITC and sulforaphane correlated (r = 0.859; p = 0.006), suggesting that broccoli shows no myrosinase selectivity among sinigrin and glucoraphanin. Measurement of AITC formation provides a novel, reliable estimation of myrosinase-dependent isothiocyanate formation suitable for use with whole vegetable food samples.

Influence of seasonal variation and methyl jasmonate mediated induction of glucosinolate biosynthesis on quinone reductase activity in broccoli florets

Methyl jasmonate spray treatments (250 μM) were utilized to alter glucosinolate composition in the florets of the commercial broccoli F1 hybrids 'Pirate', 'Expo', 'Green Magic', 'Imperial', and 'Gypsy' grown in replicated field plantings in 2009 and 2010. MeJA treatment significantly increased glucoraphanin (11%), gluconasturtiin (59%), and neoglucobrassicin (248%) concentrations and their hydrolysis products including sulforaphane (152%), phenethyl isothiocyanate (318%), N-methoxyindole-3-carbinol (313%), and neoascorbigen (232%) extracted from florets of these genotypes over two seasons. Increased quinone reductase (QR) activity was significantly correlated with increased levels of sulforaphane, N-methoxyindole-3-carbinol, and neoascorbigen. Partitioning experiment-wide trait variances indicated that the variability in concentrations of sulforaphane (29%), neoascorbigen (48%), and QR activity (72%) was influenced by year-associated weather variables, whereas variation in neoglucobrassicin (63%) and N-methoxyindole-3-carbinol (46%) concentrations was primarily attributed to methyl jasmonate treatment. These results suggest that methyl jasmonate treatment can enhance QR inducing activity by increased hydrolysis of glucoraphanin into sulforaphane and the hydrolysis products of neoglucobrassicin.