Characterization of products from the reaction of glucosinolate-derived isothiocyanates with cysteine and lysine derivatives formed in either model systems or broccoli sprouts

Non-enzymatic degradation of aliphatic Brassicaceae isothiocyanates during aqueous heat treatment

Glucosinolate-derived isothiocyanates are valuable for human health as they exert health promoting effects. As thermal food processing could affect their levels in a structure dependent way, the stability and reactivity of 12 Brassicaceae isothiocyanates during aqueous heating at 100 °C and pH 5-8 were investigated. The formation of their corresponding amines and N,N'-dialk(en)yl thioureas was quantified. Further, the potential to form odor active compounds was investigated by HRGC-MS-olfactometry. A strong structure-reactivity relationship was found and shorter side chains and electron withdrawing groups increase the reactivity of isothiocyanates. 3-(Methylsulfonyl)-propyl isothiocyanate was least stable. The main products are the corresponding amines (up to 69% recovery) and formation of N,N'-dialk(en)yl thioureas is only relevant at neutral to basic pH values. Apart from allyl isothiocyanate also 3-(methylthio)propyl isothiocyanate is precursor to many sulfur-containing odor active compounds. Thus, the isothiocyanate-structure affects their levels but also contributes to the flavor of boiled Brassicaceae vegetables.

Nutritional Sources and Anticancer Potential of Phenethyl Isothiocyanate: Molecular Mechanisms and Therapeutic Insights

Phenethyl isothiocyanate (PEITC), a compound derived from cruciferous vegetables, has garnered attention for its anticancer properties. This review synthesizes existing research on PEITC, focusing on its mechanisms of action in combatting cancer. PEITC has been found to be effective against various cancer types, such as breast, prostate, lung, colon, and pancreatic cancers. Its anticancer activities are mediated through several mechanisms, including the induction of apoptosis (programmed cell death), inhibition of cell proliferation, suppression of angiogenesis (formation of new blood vessels that feed tumors), and reduction of metastasis (spread of cancer cells to new areas). PEITC targets crucial cellular signaling pathways involved in cancer progression, notably the Nuclear Factor kappa-light-chain-enhancer of activated B cells (NF-κB), Protein Kinase B (Akt), and Mitogen-Activated Protein Kinase (MAPK) pathways. These findings suggest PEITC's potential as a therapeutic agent against cancer. However, further research is necessary to determine the optimal dosage, understand its bioavailability, and assess potential side effects. This will be crucial for developing PEITC-based treatments that are both effective and safe for clinical use in cancer therapy.

Degradation of glucosinolates and formation of isothiocyanates, nitriles, amines, and N,N'-dialk(en)yl thioureas during domestic boiling of red cabbage

Red cabbage is a popular vegetable in Central Europe and a rich source of glucosinolates (GLSs). Upon hydrolysis, GLSs form health-promoting isothiocyanates (ITCs), but also nitriles and epithionitriles. Recently, ITCs were shown to undergo further hydrolysis, yielding amines. Here, we analyzed the degradation of GLSs and the formation of ITCs, nitriles, epithionitriles, and amines during domestic-like cooking of red cabbage with addition of vinegar or baking soda. Both additives strongly affected the stability of GLSs and the formation of nitriles during boiling. Primary amines were found as a major degradation product of GLSs. In control and vinegar samples, formation of methylsulfinylalkyl amines increased during boiling. Additionally, for the first time, the formation of several N,N'-dialk(en)yl thioureas during boiling of Brassica vegetables was demonstrated, resulting from the reaction of GLS-derived ITCs and amines, and they were subsequently quantified. As references, five N,N'-dialk(en)yl thioureas were synthesized and characterized by NMR and HRMS.

Insights into the loss of glucoraphanin in post-harvested broccoli--Possible involvement of the declined supply capacity of sulfur donor

The loss of characteristic nutrient glucoraphanin during the shelf life seriously affects the nutritional quality of broccoli. Here, we monitored the changes in the levels of sulfur donors (cysteine and glutathione) required for glucoraphanin biosynthesis. Similar to glucoraphanin, cysteine content decreased sharply. Continuous down-regulation of BoCysK1 and BoCysK2 genes encoding cysteine synthase might account for cysteine loss. Contrarily, glutathione content accumulated steadily, which might owe to the up-regulation of biosynthetic gene (BoEC1). Additionally, the change of malondialdehyde content was positively correlated with glutathione, implying that oxidative stress might stimulate glutathione accumulation. Nevertheless, the expression of BoGSTF11 gene encoding glutathione S-transferases was down-regulated, which blocked the supply of glutathione. The increase in the content of raphanusamic acid (degradation product) indicated that insufficient supply of sulfur donors not only could constrain the biosynthesis of glucoraphanin but also triggered its degradation.

The Volatile Profile of Brussels Sprouts (Brassica oleracea Var. gemmifera) as Affected by Pulsed Electric Fields in Comparison to Other Pretreatments, Selected to Steer (Bio)Chemical Reactions

Pulsed electric fields (PEF) at low field strength is considered a non-thermal technique allowing membrane permeabilization in plant-based tissue, hence possibly impacting biochemical conversions and the concomitant volatile profile. Detailed studies on the impact of PEF at low field strength on biochemical conversions in plant-based matrices are scarce but urgently needed to provide the necessary scientific basis allowing to open a potential promising field of applications. As a first objective, the effect of PEF and other treatments that aim to steer biochemical conversions on the volatile profile of Brussels sprouts was compared in this study. As a second objective, the effect of varying PEF conditions on the volatile profile of Brussels sprouts was elucidated. Volatile fingerprinting was used to deduce whether and which (bio)chemical reactions had occurred. Surprisingly, PEF at 1.01 kV/cm and 2.7 kJ/kg prior to heating was assumed not to have caused significant membrane permeabilization since similar volatiles were observed in the case of only heating, as opposed to mixing. A PEF treatment with an electrical field strength of 3.00 kV/cm led to a significantly higher formation of certain enzymatic reaction products, being more pronounced when combined with an energy input of 27.7 kJ/kg, implying that these PEF conditions could induce substantial membrane permeabilization. The results of this study can be utilized to steer enzymatic conversions towards an intended volatile profile of Brussels sprouts by applying PEF.

Formation of volatile sulfur compounds and S-methyl-l-cysteine sulfoxide in Brassica oleracea vegetables

Besides glucosinolates, Brassica vegetables accumulate sulfur-containing (+)-S-methyl-l-cysteine sulfoxide (SMCSO, methiin), mainly known from Allium vegetables. Such (+)-S-alk(en)yl-l-cysteine sulfoxides can degrade to volatile organosulfur compounds (VOSCs), which have been linked to health beneficial effects. In the present study, the accumulation of SMCSO and the formation of VOSCs was investigated in Brassica oleracea vegetables. SMCSO content of commercially available white and red cabbages was monitored over a three-month period and linked with the formation of VOSCs. S-Methyl methanethiosulfinate was the main VOSC released from SMCSO. Upon heating, it degraded to dimethyltrisulfide and dimethyldisulfide, which were less abundant in fresh homogenates. SMCSO made up approximately 1% of the dry matter of cabbages and the overall contents were similar in white and red cabbages (3.2-10.2 and 3.9-10.3 µmol/g fresh weight, respectively). Using proteome profiling it was shown that recovery of VOSCs correlated with abundance of two isoforms of cystine lyase.

Assessing Bioavailability and Bioactivity of 4-Hydroxythiazolidine-2-Thiones, Newly Discovered Glucosinolate Degradation Products Formed During Domestic Boiling of Cabbage

Glucosinolates are plant secondary metabolites found in cruciferous vegetables (Brassicaceae) that are valued for their potential health benefits. Frequently consumed representatives of these vegetables, for example, are white or red cabbage, which are typically boiled before consumption. Recently, 3-alk(en)yl-4-hydroxythiazolidine-2-thiones were identified as a class of thermal glucosinolate degradation products that are formed during the boiling of cabbage. Since these newly discovered compounds are frequently consumed, this raises questions about their potential uptake and their possible bioactive functions. Therefore, 3-allyl-4-hydroxythiazolidine-2-thione (allyl HTT) and 4-hydroxy-3-(4-(methylsulfinyl) butyl)thiazolidine-2-thione (4-MSOB HTT) as degradation products of the respective glucosinolates sinigrin and glucoraphanin were investigated. After consumption of boiled red cabbage broth, recoveries of consumed amounts of the degradation products in urine collected for 24 h were 18 ± 5% for allyl HTT and 21 ± 4% for 4-MSOB HTT (mean ± SD, n = 3). To investigate the stability of the degradation products during uptake and to elucidate the uptake mechanism, both an in vitro stomach and an in vitro intestinal model were applied. The results indicate that the uptake of allyl HTT and 4-MSOB HTT occurs by passive diffusion. Both compounds show no acute cell toxicity, no antioxidant potential, and no change in NAD(P)H dehydrogenase quinone 1 (NQO1) activity up to 100 μM. However, inhibition of glycogen synthase kinases-3 (GSK-3) in the range of 20% for allyl HTT for the isoform GSK-3β and 29% for 4-MSOB HTT for the isoform GSK-3α at a concentration of 100 μM was found. Neither health-promoting nor toxic effects of 3-alk(en)yl-4-hydroxythiazolidine-2-thiones were found in the four tested assays carried out in this study, which contrasts with the properties of other glucosinolate degradation products, such as isothiocyanates.

Plant pathogenic bacterium can rapidly evolve tolerance to an antimicrobial plant allelochemical

Crop losses to plant pathogens are a growing threat to global food security and more effective control strategies are urgently required. Biofumigation, an agricultural technique where Brassica plant tissues are mulched into soils to release antimicrobial plant allelochemicals called isothiocyanates (ITCs), has been proposed as an environmentally friendly alternative to agrochemicals. Whilst biofumigation has been shown to suppress a range of plant pathogens, its effects on plant pathogenic bacteria remain largely unexplored. Here, we used a laboratory model system to compare the efficacy of different types of ITCs against Ralstonia solanacearum plant bacterial pathogen. Additionally, we evaluated the potential for ITC-tolerance evolution under high, intermediate, and low transfer frequency ITC exposure treatments. We found that allyl-ITC was the most efficient compound at suppressing R. solanacearum growth, and its efficacy was not improved when combined with other types of ITCs. Despite consistent pathogen growth suppression, ITC tolerance evolution was observed in the low transfer frequency exposure treatment, leading to cross-tolerance to ampicillin beta-lactam antibiotic. Mechanistically, tolerance was linked to insertion sequence movement at four positions in genes that were potentially associated with stress responses (H-NS histone like protein), cell growth and competitiveness (acyltransferase), iron storage ([2-Fe-2S]-binding protein) and calcium ion sequestration (calcium-binding protein). Interestingly, pathogen adaptation to the growth media also indirectly selected for increased ITC tolerance through potential adaptations linked with metabolism and antibiotic resistance (dehydrogenase-like protein) and transmembrane protein movement (Tat pathway signal protein). Together, our results suggest that R. solanacearum can rapidly evolve tolerance to allyl-ITC plant allelochemical which could constrain the long-term efficiency of biofumigation biocontrol and potentially shape pathogen evolution with plants.

High-Throughput Assessment of the Abiotic Stability of Test Chemicals in In Vitro Bioassays

Abiotic stability of chemicals is not routinely tested prior to performing in vitro bioassays, although abiotic degradation can reduce the concentration of test chemicals leading to the formation of active or inactive transformation products, which may lead to misinterpretation of bioassay results. A high-throughput workflow was developed to measure the abiotic stability of 22 test chemicals in protein-rich aqueous media under typical bioassay conditions at 37 °C for 48 h. These test chemicals were degradable in the environment according to a literature review. The chemicals were extracted from the exposure media at different time points using a novel 96-pin solid-phase microextraction. The conditions were varied to differentiate between various reaction mechanisms. For most hydrolyzable chemicals, pH-dependent degradation in phosphate-buffered saline indicated that acid-catalyzed hydrolysis was less important than reactions with hydroxide ions. Reactions with proteins were mainly responsible for the depletion of the test chemicals in the media, which was simulated by bovine serum albumin (BSA) and glutathione (GSH). 1,2-Benzisothiazol-3(2H)-one, 2-methyl-4-isothiazolinone, and l-sulforaphane reacted almost instantaneously with GSH but not with BSA, indicating that GSH is a good proxy for reactivity with electrophilic amino acids but may overestimate the actual reaction with three-dimensional proteins. Chemicals such as hydroquinones or polyunsaturated chemicals are prone to autoxidation, but this reaction is difficult to differentiate from hydrolysis and could not be simulated by the oxidant N-bromosuccinimide. Photodegradation played a minor role because cells are exposed in incubators in the dark and simulations with high light intensities did not yield realistic degradation. Stability predictions from various in silico prediction models for environmental conditions can give initial indications of the stability but were not always consistent with the experimental stability in bioassays. As the presented workflow can be performed in high throughput under realistic bioassay conditions, it can be used to provide an experimental database for developing bioassay-specific stability prediction models.

Assessment of Methodological Pipelines for the Determination of Isothiocyanates Derived from Natural Sources

Isothiocyanates are biologically active secondary metabolites liberated via enzymatic hydrolysis of their sulfur enriched precursors, glucosinolates, upon tissue plant disruption. The importance of this class of compounds lies in their capacity to induce anti-cancer, anti-microbial, anti-inflammatory, neuroprotective, and other bioactive properties. As such, their isolation from natural sources is of utmost importance. In this review article, an extensive examination of the various parameters (hydrolysis, extraction, and quantification) affecting the isolation of isothiocyanates from naturally-derived sources is presented. Overall, the effective isolation/extraction and quantification of isothiocyanate is strongly associated with their chemical and physicochemical properties, such as polarity-solubility as well as thermal and acidic stability. Furthermore, the successful activation of myrosinase appears to be a major factor affecting the conversion of glucosinolates into active isothiocyanates.

Characterization of Conjugates between α-Lactalbumin and Benzyl Isothiocyanate-Effects on Molecular Structure and Proteolytic Stability

In complex foods, bioactive secondary plant metabolites (SPM) can bind to food proteins. Especially when being covalently bound, such modifications can alter the structure and, thus, the functional and biological properties of the proteins. Additionally, the bioactivity of the SPM can be affected as well. Consequently, knowledge of the influence of chemical modifications on these properties is particularly important for food processing, food safety, and nutritional physiology. As a model, the molecular structure of conjugates between the bioactive metabolite benzyl isothiocyanate (BITC, a hydrolysis product of the glucosinolate glucotropaeolin) and the whey protein α-lactalbumin (α-LA) was investigated using circular dichroism spectroscopy, anilino-1-naphthalenesulfonic acid fluorescence, and dynamic light scattering. Free amino groups were determined before and after the BITC conjugation. Finally, mass spectrometric analysis of the BITC-α-LA protein hydrolysates was performed. As a result of the chemical modifications, a change in the secondary structure of α-LA and an increase in surface hydrophobicity and hydrodynamic radii were documented. BITC modification at the ε-amino group of certain lysine side chains inhibited tryptic hydrolysis. Furthermore, two BITC-modified amino acids were identified, located at two lysine side chains (K32 and K113) in the amino acid sequence of α-LA.

Benzyl isothiocyanate-modified α-lactalbumin - Two-dimensional high-performance thin-layer chromatography for analyzing modified peptides

In complex food matrices, non-directed reactions between food proteins and secondary plant metabolites (SPM) are conceivable. In this study, the interaction between the bioactive metabolite from garden cress (Lepidium sativum) and selected Brassicaceae - benzyl isothiocyanate (BITC) - and the dairy protein α-lactalbumin (α-LA) was investigated. It was focused on monitoring the proteolytic degradation behaviour of unmodified and BITC-modified α-LA with two-dimensional high-performance thin-layer chromatography (2D-HPTLC). The two-dimensional approach of HPTLC offers high resolution in the separation of complex peptide mixtures and might enable differentiation of protein modifications. Based on the specific peptide patterns of native and modified peptides, conclusions can be drawn about differences in protein/peptide polarity, location of a modification, and digestibility. The aim was to characterize tryptically hydrolyzed unmodified and BITC-modified peptides using the 2D method and to investigate the influence of BITC modification of α-LA on polarity and digestibility. To determine the repeatability of peptide separation by 2D-HPTLC, the unmodified and BITC-modified protein hydrolyzates were separated six times. The absolute standard deviations between the retardation factors of the individual peptide spots varied between 0.52 and 4.79 mm for the x-coordinates and between 0.41 and 6.47 mm for the y-coordinates for all three samples. Here, the mean relative standard deviations ranged from 5.80 to 10.4% for the x-coordinates and from 5.91 to 18.3% for the y-coordinates. The results of the tryptic hydrolysis indicated that, depending on the concentration of BITC used, the modification sterically hinders the cleavage sites for the enzyme, resulting in a reduced digestibility. Covalent binding of the hydrophobic BITC altered the digestibility and polarity of the protein, leading to a difference in peptide patterns between the unmodified and modified α-LA. It was concluded that the reaction was undirected, resulting in a mixture of unmodified and modified peptides, and that elongated modified peptides were formed by BITC blocking of trypsin cleavage sites.

The degradation kinetics and mechanism of moringin in aqueous solution and the cytotoxicity of degraded products

In this work, we investigated the degradation of moringin (4-[(α-l-rhamnosyloxy)benzyl]-isothiocyanate), a major bioactive isothiocyanate (ITC) found in moringa seeds (Moringa oleifera Lam), at various food processing conditions. Moringin degrades rapidly to several water-soluble products via a pseudo-first-order kinetics. By analyzing the reaction products, the degradation mechanism was found to be through hydrolyzing to (A) 1-O-(4-hydroxymethylphenyl) α-l-rhamnopyranoside (rhamnobenzyl alcohol RBA) or (B) rhamnobenzylamine. The formed amine further reacts with moringin to form N,N'-bis{4-[(α-l-rhamnosyloxy)benzyl]}thiourea (di-rhamnobenzyl thiourea, DRBTU). In addition, moringin isomerizes to 4-[(α-l-rhamnosyloxy)benzyl]thiocyanate (RBTC), which further reacts with moringin to form S,N-bis{4-[(α-l-rhamnosyloxy)benzyl]}-dithiocarbamate (DRBDTC). Furthermore, pH was found to have an effect on the degradation of moringin. RBA and RBTC were major degraded products in neutral and acidic conditions while thiourea (DRBTU) was in alkaline condition. Although moringin showed higher cytotoxicity to cancer cells, its degraded products showed very weak or no activities, suggesting that the isothiocyanate group of ITCs is essential for their cancer chemoprevention activities.

The flavor of Chinese kale sprouts is affected by genotypic variation of glucosinolates and their breakdown products

Metabolic profiling of glucosinolates and their breakdown products in sprouts of 22 Chinese kale (Brassica oleracea var. alboglabra, BOA) varieties were investigated by using high-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS). Relationships between glucosinolate metabolites and flavor of Chinese kale sprouts were also analyzed. Results showed that compositions and contents of both glucosinolates and their breakdown products varied greatly among different varieties of Chinese kale sprouts. Gluconapin and 4,5-Epithio-pentanenitrile were the dominant glucosinolate and glucosinolate breakdown product in Chinese kale sprouts, respectively. Gluconapin and glucobrassicin were significantly related to bitterness (r = 0.577, 0.648, respectively; p < 0.05). BOA 1 and BOA 13, BOA 3 and BOA 10 are good candidates for future breeding programs since the former two varieties have light bitterness and pungency, and the latter two varieties contain high levels of glucosinolate breakdown products such as isothiocyanates and epithionitriles in sprouts.

Immunological Analysis of Isothiocyanate-Modified α-Lactalbumin Using High-Performance Thin Layer Chromatography

Undirected modifications between food proteins and secondary plant metabolites can occur during food processing. The results of covalent interactions can alter the functional and biological properties of the proteins. The present work studied the extent of which covalent conjugation of the bioactive metabolite benzyl isothiocyanate (BITC; a glucosinolate breakdown product) to the whey protein α-lactalbumin affects the protein’s allergenicity. Additional to the immunological analysis of native untreated and BITC-modified α-lactalbumin, the analysis of antigenic properties of proteolytically digested protein derivatives was also performed by high performance thin layer chromatography and immunostaining. As a result of the chemical modifications, structural changes in the protein molecule affected the allergenic properties. In this process, epitopes are destroyed or inactivated, but at the same time, buried epitopes can be exposed or newly formed, so that the net effect was an increase in allergenicity, in this case. Results from the tryptic hydrolysis suggest that BITC conjugation sterically hindered the cleavage sites for the enzyme, resulting in reduced digestibility and allergenicity. Residual antigenicity can be still present as short peptide fragments that provide epitopes. The desire to make food safer for allergy sufferers and to protect sensitized individuals from an allergenic reaction makes it clear that the detection of food antigens is mandatory; especially by considering protein interactions.

Approaches for enhancing the stability and formation of sulforaphane

The isothiocyanate sulforaphane (SF) is one of the most potent naturally occurring Phase 2 enzymes inducers derived from brassica vegetables like broccoli, cabbage, brussel sprouts, etc. Ingestion of broccoli releases SF via hydrolysis of glucoraphanin (GRP) by plant myrosinase and/or intestinal microbiota. However, both SF and plant myrosinase are thermal-labile, and the epithiospecifier protein (ESP) directs the hydrolysis of GRP toward formation of sulforaphane nitrile instead of SF. In addition, bacterial myrosinase has low hydrolyzing efficiency. In this review, we discuss strategies that could be employed to improve the stability of SF, increase SF formation during thermal and non-thermal processing of broccoli, and enhance the myrosinase-like activity of the gut microbiota. Furthermore, new cooking methods or blanching technologies should be developed to maintain myrosinase activity, and novel thermostable myrosinase and/or microbes with high SF producing abilities should also be developed.

Detoxification of plant defensive glucosinolates by an herbivorous caterpillar is beneficial to its endoparasitic wasp

Plant chemical defences impact not only herbivores, but also organisms in higher trophic levels that prey on or parasitize herbivores. While herbivorous insects can often detoxify plant chemicals ingested from suitable host plants, how such detoxification affects endoparasitoids that use these herbivores as hosts is largely unknown. Here, we used transformed plants to experimentally manipulate the major detoxification reaction used by Plutella xylostella (diamondback moth) to deactivate the glucosinolate defences of its Brassicaceae host plants. We then assessed the developmental, metabolic, immune, and reproductive consequences of this genetic manipulation on the herbivore as well as its hymenopteran endoparasitoid Diadegma semiclausum. Inhibition of P. xylostella glucosinolate metabolism by plant-mediated RNA interference increased the accumulation of the principal glucosinolate activation products, the toxic isothiocyanates, in the herbivore, with negative effects on its growth. Although the endoparasitoid manipulated the excretion of toxins by its insect host to its own advantage, the inhibition of herbivore glucosinolate detoxification slowed endoparasitoid development, impaired its reproduction, and suppressed the expression of genes of a parasitoid-symbiotic polydnavirus that aids parasitism. Therefore, the detoxification of plant glucosinolates by an herbivore lowers its toxicity as a host and benefits the parasitoid D. semiclausum at multiple levels.

Control of pathogenic and spoilage bacteria in meat and meat products by high pressure: Challenges and future perspectives

High-pressure processing is among the most widely used nonthermal intervention to reduce pathogenic and spoilage bacteria in meat and meat products. However, resistance of pathogenic bacteria strains in meats at the current maximum commercial equipment of 600 MPa questions the ability of inactivation by its application in meats. Pathogens including Escherichia coli, Listeria, and Salmonelle, and spoilage microbiota including lactic acid bacteria dominate in raw meat, ready-to-eat, and packaged meat products. Improved understanding on the mechanisms of the pressure resistance is needed for optimizing the conditions of pressure treatment to effectively decontaminate harmful bacteria. Effective control of the pressure-resistant pathogens and spoilage organisms in meats can be realized by the combination of high pressure with application of mild temperature and/or other hurdles including antimicrobial agents and/or competitive microbiota. This review summarized applications, mechanisms, and challenges of high pressure on meats from the perspective of microbiology, which are important for improving the understanding and optimizing the conditions of pressure treatment in the future.

Bioactive Compounds and Bioactivities of Brassica oleracea L. var. Italica Sprouts and Microgreens: An Updated Overview from a Nutraceutical Perspective

Sprouts and microgreens, the edible seedlings of vegetables and herbs, have received increasing attention in recent years and are considered as functional foods or superfoods owing to their valuable health-promoting properties. In particular, the seedlings of broccoli (Brassica oleracea L. var. Italica) have been highly prized for their substantial amount of bioactive constituents, including glucosinolates, phenolic compounds, vitamins, and essential minerals. These secondary metabolites are positively associated with potential health benefits. Numerous in vitro and in vivo studies demonstrated that broccoli seedlings possess various biological properties, including antioxidant, anticancer, anticancer, antimicrobial, anti-inflammatory, anti-obesity and antidiabetic activities. The present review summarizes the updated knowledge about bioactive compounds and bioactivities of these broccoli products and discusses the relevant mechanisms of action. This review will serve as a potential reference for food selections of consumers and applications in functional food and nutraceutical industries.

Methyl Jasmonate Treatment of Broccoli Enhanced Glucosinolate Concentration, Which Was Retained after Boiling, Steaming, or Microwaving

Exogenous methyl jasmonate (MeJA) treatment was known to increase the levels of neoglucobrassicin and their bioactive hydrolysis products in broccoli (Brassica oleracea var. italica), but the fate of MeJA-induced glucosinolates (GSLs) after various cooking methods was unknown. This study measured the changes in GSLs and their hydrolysis compounds in broccoli treated with MeJA and the interaction between MeJA and cooking treatments. All cooked MeJA-treated broccoli contained significantly more GSLs than untreated broccoli (p < 0.05). After 5 min of cooking (boil, steam, microwave), MeJA-treated broccoli still contained 1.6- to 2.3-fold higher GSL content than untreated broccoli. Neoglucobrassicin hydrolysis products were also significantly greater in steamed and microwaved MeJA-treated broccoli. The results show that exogenous MeJA treatment increases neoglucobrassicin and its hydrolysis compounds in broccoli even after cooking. Once the positive and negative effects of these compounds are better understood, the results of this experiment can be a valuable tool to help food scientists, nutrition scientists, and dieticians determine how to incorporate raw or cooked broccoli and Brassica vegetables in the diet.

Chemical Aspects of Biological Activity of Isothiocyanates and Indoles, the Products of Glucosinolate Decomposition

There is growing evidence that cancer chemoprevention employing natural, bioactive compounds may halt or at least slow down the different stages of carcinogenesis. A particularly advantageous effect is attributed to derivatives of sulfur-organic phytochemicals, such as glucosinolates (GLs) synthesized mainly in Brassicaceae plant family. GLs are hydrolysed enzymatically to bioactive isothiocyanates (ITC) and indoles, which exhibit strong anti-inflammatory and anti-carcinogenic activity. Highly bioavailable electrophilic ITC are of particular interest, as they can react with nucleophilic groups of important biomolecules to form dithiocarbamates, thiocarbamates and thioureas. These modifications seem responsible for the chemopreventive activity, but also for genotoxicity and mutagenicity. It was documented that ITC can permanently bind to important biomolecules such as glutathione, cytoskeleton proteins, transcription factors NF-κB and Nrf2, thiol-disulfide oxidoreductases, proteasome proteins or heat shock proteins. Furthermore, ITC may also affect epigenetic regulation of gene expression, e.g. by inhibition of histone deacetylases. Some other derivatives of glucosinolates, especially indoles, are able to form covalent bonds with nucleobases in DNA, which may result in genotoxicity and mutagenicity. This article summarizes the current state of knowledge about glucosinolates and their degradation products in terms of possible interactions with reactive groups of cellular molecules.

Tritrophic metabolism of plant chemical defenses and its effects on herbivore and predator performance

Insect herbivores are frequently reported to metabolize plant defense compounds, but the physiological and ecological consequences are not fully understood. It has rarely been studied whether such metabolism is genuinely beneficial to the insect, and whether there are any effects on higher trophic levels. Here, we manipulated the detoxification of plant defenses in the herbivorous pest diamondback moth (Plutella xylostella) to evaluate changes in fitness, and additionally examined the effects on a predatory lacewing (Chrysoperla carnea). Silencing glucosinolate sulfatase genes resulted in the systemic accumulation of toxic isothiocyanates in P. xylostella larvae, impairing larval development and adult reproduction. The predatory lacewing C. carnea, however, efficiently degraded ingested isothiocyanates via a general conjugation pathway, with no negative effects on survival, reproduction, or even prey preference. These results illustrate how plant defenses and their detoxification strongly influence herbivore fitness but might only subtly affect a third trophic level.

Isothiocyanates from Brassica Vegetables-Effects of Processing, Cooking, Mastication, and Digestion

The formation of health-beneficial isothiocyanates (ITCs) from glucosinolates depends on a wide variety of plant-intrinsic factors (e.g., concentration of glucosinolates, activity of myrosinase, and specifier proteins) and on a multitude of extrinsic postharvest factors such as the conditions used during industrial processing, domestic preparation, mastication, and digestion. All of these factors contribute to a large variability in the formation of ITCs (and other breakdown products), as well as their intake and absorption upon consumption of Brassica vegetables. This uncertainty in ITC intake and absorption is a barrier for the determination of an optimal Brassica vegetable consumption pattern. In this review, the intrinsic and extrinsic factors that affect the formation, intake, and absorption of ITCs are described according to the most recent findings. The focus of this review includes the hydrolysis reaction mechanisms, the elucidation of the primary factors that play a role in the hydrolysis reaction, the influence of processing and cooking conditions, the effect of chewing, and the roles of the gastric and upper intestinal phases, including the effect of the meal composition (e.g., the effect of other meal compounds present during digestion) on the potential formation of ITCs.

Diverse Excretion Pathways of Benzyl Glucosinolate in Humans after Consumption of Nasturtium (Tropaeolum majus L.)-A Pilot Study

SCOPE

Different metabolic and excretion pathways of the benzyl glucosinolate breakdown products benzyl isothiocyanate and benzyl cyanide are investigated to obtain information about their multiple fate after ingestion. Detailed focus is on the so far underestimated transformation/excretion pathways-protein conjugation and exhalation.

METHODS AND RESULTS

Metabolites, protein conjugates, and non-conjugated isothiocyanates are determined in plasma, urine, and breath of seven volunteers after consuming freeze-dried nasturtium or bread enriched with nasturtium. Samples are collected up to 48 h at selected time points. The metabolites of the mercapturic acid pathway are detectable in plasma up to 24 h after consumption. Additionally, mercapturic acid is the main metabolite in urine, but non-conjugated benzyl isothiocyanate is detectable as well. Protein conjugates show high amounts in plasma even 48 h after consumption. In breath, benzyl isothiocyanate and benzyl cyanide are detectable up to 48 h after consumption.

CONCLUSION

Isothiocyanates are not only metabolized via the mercapturic acid pathway, but also form protein conjugates in blood and are exhaled. To balance intake and excretion, it is necessary to investigate all potential metabolites and excretion routes. This has important implications for the understanding of physiological and pharmacological effects of isothiocyanate-containing products.

In Vitro Determination of Protein Conjugates in Human Cells by LC-ESI-MS/MS after Benzyl Isothiocyanate Exposure

Glucosinolates and their breakdown products, especially isothiocyanates (ITCs), are hypothesized to exert a broad range of bioactivities. However, physiological mechanisms are not yet completely understood. In this study, formation of protein conjugates after incubation with benzyl isothiocyanate (BITC) was investigated in vitro. A survey of protein conjugates was done by determining BITC cysteine and lysine amino acid conjugates after protein digestion. Therefore, a liquid chromatography-tandem mass spectrometry (LC-ESI-MS/MS) method was developed and validated. Stability studies showed that cysteine conjugates are not stable under alkaline conditions, and lysine conjugates did not show any correlation to pH values, although stability increased at low temperatures. Lysine conjugates were the preferred form of protein conjugates, and longer BITC exposure times led to higher amounts. Knowledge about the reaction sites of ITCs in eukaryotic cells may help to understand the mode of action of ITCs leading to health promoting as well as toxicological effects in humans.

Arabidopsis mutants impaired in glutathione biosynthesis exhibit higher sensitivity towards the glucosinolate hydrolysis product allyl-isothiocyanate

Upon tissue damage the plant secondary metabolites glucosinolates can generate various hydrolysis products, including isothiocyanates (ITCs). Their role in plant defence against insects and pest and their potential health benefits have been well documented, but our knowledge regarding the endogenous molecular mechanisms of their effect in plants is limited. Here we investigated the effect of allyl-isothiocyanate (AITC) on Arabidopsis thaliana mutants impaired in homeostasis of the low-molecular weight thiol glutathione. We show that glutathione is important for the AITC-induced physiological responses, since mutants deficient in glutathione biosynthesis displayed a lower biomass and higher root growth inhibition than WT seedlings. These mutants were also more susceptible than WT to another ITC, sulforaphane. Sulforaphane was however more potent in inhibiting root growth than AITC. Combining AITC with the glutathione biosynthesis inhibitor L-buthionine-sulfoximine (BSO) led to an even stronger phenotype than observed for the single treatments. Furthermore, transgenic plants expressing the redox-sensitive fluorescent biomarker roGFP2 indicated more oxidative conditions during AITC treatment. Taken together, we provide genetic evidence that glutathione plays an important role in AITC-induced growth inhibition, although further studies need to be conducted to reveal the underlying mechanisms.

Glucoraphanin and sulforaphane evolution during juice preparation from broccoli sprouts

Broccoli sprouts are considered functional food as they are naturally enriched in glucoraphanin (GR) that is the biological precursor of the anticancer compound sulforaphane (SFN). Due to its health promoting value, also broccoli sprout juice is becoming very popular. The present study aimed to quantitatively assess the conversion of GR to its hydrolysis products, SFN and SFN-nitrile, during the juice preparation process. We demonstrated that SFN plus SFN-nitrile yield from glucoraphanin is quite low (≈25%) and that some SFN is lost during the juice preparation partially due to the spontaneous conversion to sulforaphane-amine or conjugation to GSH and proteins naturally present in the juice. Our results demonstrate that the detection of the sole SFN free form does not provide reliable information about the real concentration of this functional compound in the juice.

Food as Pharma? The Case of Glucosinolates

BACKGROUND

Glucosinolates (GLSs) are dietary plant secondary metabolites occurring in the order Brassicales with potential health effects, in particular as anti-carcinogenic compounds. GLSs are converted into a variety of breakdown products (BPs) upon plant tissue damage and by the gut microbiota. GLS biological activity is related to BPs rather than to GLSs themselves.

METHODS

we have reviewed the most recent scientific literature on the metabolic fate and the biological effect of GLSs with particular emphasis on the epidemiological evidence for health effect and evidence from clinical trials. An overview of potential molecular mechanisms underlying GLS biological effect is provided. The potential toxic or anti-nutritional effect has also been discussed.

RESULTS

Epidemiological and human in vivo evidence point towards a potential anti-cancer effect for sulforaphane, indole-3-carbinol and 3,3-diindolylmethane. A number of new human clinical trials are on-going and will likely shed further light on GLS protective effect towards cancer as well as other diseases. BPs biological effect is the results of a plurality of molecular mechanisms acting simultaneously which include modulation of xenobiotic metabolism, modulation of inflammation, regulation of apoptosis, cell cycle arrest, angiogenesis and metastasis and regulation of epigenetic events. BPs have been extensively investigated for their protective effect towards cancer but in recent years the interest also includes other diseases.

CONCLUSION

It appears that certain BPs may protect against and may even represent a therapeutic strategy against several forms of cancer. Whether this latter effect can be achieved through diet or supplements should be investigated more thoroughly.

The major glucosinolate hydrolysis product in rocket (Eruca sativa L.), sativin, is 1,3-thiazepane-2-thione: Elucidation of structure, bioactivity, and stability compared to other rocket isothiocyanates

Rocket is rich in glucosinolates and valued for its hot and spicy taste. Here we report the structure elucidation, bioactivity, and stability of the mainly formed glucosinolate hydrolysis product, namely sativin, which was formerly thought to be 4-mercaptobutyl isothiocyanate. However, by NMR characterization we revealed that sativin is in fact 1,3-thiazepane-2-thione, a tautomer of 4-mercaptobutyl isothiocyanate with 7-membered ring structure and so far unknown. This finding was further substantiated by conformation sampling using molecular modeling and total enthalpy calculation with density functional theory. During aqueous heat treatment sativin in general was quite stable, while the isothiocyanates erucin and sulforaphane were labile, having half-lives of 132 min and 56 min (pH 5, 100 °C), respectively. Moreover, using a WST-1 assay, we found that sativin did not reduce cell viability of HepG2 cells in a range of 0.3-30 µM, and, therefore, exhibited no cytotoxic effects in this cell line.

Determination of isothiocyanate-protein conjugates in milk and curd after adding garden cress (Lepidium sativum L.)

Isothiocyanates (ITC) play an important role in health promotion and cancer prevention due to their anti-bacterial, anti-inflammatory, and anti-cancerogenic properties. However, ITC are highly reactive so that a reaction with further food components is very likely. For example, a reaction of ITC with nucleophilic amino acid side chains of proteins such as cysteine and lysine can occur, reducing the bioavailability of indispensable amino acids and protein functions may be altered. Therefore, it is of great interest to investigate the fate of ITC in the food matrix. Accordingly, the aim of the present study was to investigate the interaction of milk proteins and the ITC benzyl isothiocyanate (BITC) and allyl isothiocyanate (AITC) forming dithiocarbamates and thioureas in milk and curd. After incubating milk and curd with pure ITC or ITC-containing garden cress (Lepidium sativum L.), proteins were isolated, digested, and analyzed via LC-ESI-MS/MS as amino acid derivatives ("conjugates"). Protein conjugates of AITC and BITC were detected in all samples investigated. Further, the acidic pH value in curd favored the formation of dithiocarbamates over the formation of thioureas. Slightly acidic or neutral conditions like in fresh milk favored the formation of thioureas. The investigations also indicated that AITC shows a higher reactivity and dithiocarbamates are formed preferably, whereas incubation with BITC lead to less protein conjugates and the ratio of thioureas and dithiocarbamates was more balanced. In addition, amino acid modifications were often analyzed with indirect methods like measuring the decline of the amino acid residues. In this study, the modified amino acids were analyzed directly leading to more reliable results concerning the amount of modification.

Novel quinoline-3-carboxamides (Part 2): Design, optimization and synthesis of quinoline based scaffold as EGFR inhibitors with potent anticancer activity

EGFR has a key role in cell growth. Its mutation and overexpression share in epithelial malignancies and tumor growth. Quinazoline and quinoline derivatives are common anticancer intracellular inhibitors of EGFR kinase, and their optimization is an important issue for development of potent targeted anticancer agents. Based on these facts, different strategies were used for optimizing our reported quinoline-3-carboxamide compound III (EGFR IC₅₀ = 5.283 µM and MCF-7 IC₅₀ = 3.46 µM) through different molecular modeling techniques. The optimized compounds were synthesized and subjected to EGFR binding assay and accordingly some more potent inhibitors were obtained. The most potent quinoline-3-carboxamides were the furan derivative 5o; thiophene derivative 6b; and benzyloxy derivative 10 showing EGFR IC₅₀ values 2.61, 0.49 and 1.73 μM, respectively. Furthermore, the anticancer activity of compounds eliciting potent EGFR inhibition (5o, 5p, 6b, 8a, 8b, and 10) was evaluated against MCF-7 cell line where they exhibited IC₅₀ values 3.355, 3.647, 5.069, 3.617, 0.839 and 10.85 μM, respectively. Compound 6b was selected as lead structure for further optimization hoping to produce more potent EGFR inhibitors.

Isothiocyanates, Nitriles, and Epithionitriles from Glucosinolates Are Affected by Genotype and Developmental Stage in Brassica oleracea Varieties

Vegetables of the Brassica oleracea group, such as broccoli, cauliflower, and cabbage, play an important role for glucosinolate consumption in the human diet. Upon maceration of the vegetable tissue, glucosinolates are degraded enzymatically to form volatile isothiocyanates, nitriles, and epithionitriles. However, only the uptake of isothiocyanates is linked to the cancer-preventive effects. Thus, it is of great interest to evaluate especially the isothiocyanate formation. Here, we studied the formation of glucosinolates and their respective hydrolysis products in sprouts and fully developed vegetable heads of different genotypes of the five B. oleracea varieties: broccoli, cauliflower as well as white, red, and savoy cabbages. Further, the effect of ontogeny (developmental stages) during the head development on the formation of glucosinolates and their respective hydrolysis products was evaluated at three different developmental stages (mini, fully developed, and over-mature head). Broccoli and red cabbage were mainly rich in 4-(methylsulfinyl)butyl glucosinolate (glucoraphanin), whereas cauliflower, savoy cabbage and white cabbage contained mainly 2-propenyl (sinigrin) and 3-(methylsulfinyl)propyl glucosinolate (glucoiberin). Upon hydrolysis, epithionitriles or nitriles were often observed to be the main hydrolysis products, with 1-cyano-2,3-epithiopropane being most abundant with up to 5.7 μmol/g fresh weight in white cabbage sprouts. Notably, sprouts often contained more than 10 times more glucosinolates or their hydrolysis products compared to fully developed vegetables. Moreover, during head development, both glucosinolate concentrations as well as hydrolysis product concentrations changed and mini heads contained the highest isothiocyanate concentrations. Thus, from a cancer-preventive point of view, consumption of mini heads of the B. oleracea varieties is recommended.

Screening Brassicaceous Plants as Biofumigants for Management of Rhizoctonia solani AG1-IA

Brassicaceae plants rich in glucosinolates have been used as biofumigants for management of Rhizoctonia solani (teleomorph: Thanatephorus cucumeris) and other soilborne pathogens. Efficacy of brassica plant tissue has mainly been attributed to toxic isothiocyanates released upon hydrolysis of glucosinolates. Management of R. solani AG 1-IA, the causal agent of sheath blight in rice (Oryza sativa), using biofumigation, is promising but needs more validation. Biofumigation activity of nine Brassicaceae plants and two other related species were evaluated in vitro with soils from Texas, Arkansas, or Mississippi. All plants evaluated significantly suppressed the mycelium growth of R. solani AG 1-IA. Mustard (Brassica juncea) cultivars ('Brand 199', 'Ruby Streak', 'Florida Broadleaf', and 'Green Wave') consistently provided the greatest (>90%) mycelial inhibition, while sunn hemp (Crotalaria juncea) and Chinese cabbage (B. rapa) had the least suppressive effect. B. juncea 'Red Giant' and 'Sheali Hong', turnip (B. rapa), kale (B. oleracea), and arugula (Eruca sativa) showed intermediate efficacy or were inconsistent. Effects of soil pasteurization and plant tissue amendment rates were examined with B. juncea Brand 199 and Texas soil. Inhibition of mycelial growth became greater with increasing plant amendment rates up to 3.2% (wt/wt) in the soil. Soil pasteurization almost completely suppressed the release of allyl isothiocyanate (AITC). The nonpasteurized soil amended with 0.5% (wt/wt) of the plant material released 96% more AITC than the soil amended with 0.25% (wt/wt) of the plant material. The highest levels of AITC release were observed at 12 and 24 h after soil amendment, with 0.25 and 0.5% (wt/wt) of the plant material, respectively. Antifungal effects of B. juncea are attributed to dose-dependent production of volatile AITC and could be used for managing rice sheath blight caused by R. solani AG 1-IA.

Derivatization of isothiocyanates and their reactive adducts for chromatographic analysis

Isothiocyanates form adducts with a multitude of biomolecules, and these adducts need analytical methods. Likewise, analytical methods for hydrophilic isothiocyanates are needed. We considered reaction with ammonia to form thiourea derivatives. The hydrophilic, glycosylated isothiocyanate moringin, 4-(α-L-rhamnopyranosyloxy)benzyl isothiocyanate, was efficiently derivatized to the thiourea derivative by incubation with ammonia. The hydrophobic benzyl isothiocyanate was also efficiently derivatized to the thiourea derivative. The thiourea group provided a UV absorbing chromophore, and the derivatives showed expectable sodium and hydrogen adducts in ion trap mass spectrometry and were suitable for liquid chromatography analysis. Reactive dithiocarbamate adducts constitute the major type of reactive ITC adduct expected in biological matrices. Incubation of a model dithiocarbamate with ammonia likewise resulted in conversion to the corresponding thiourea derivative, suggesting that a variety of matrix-bound reactive isothiocyanate adducts can be determined using this strategy. As an example of the application of the method, recovery of moringin and benzyl isothiocyanate applied to cabbage leaf discs was studied in simulated insect feeding assays. The majority of moringin was recovered as native isothiocyanate, but a major part of benzyl isothiocyanate was converted to reactive adducts.

Inspired by Nature: The use of Plant-derived Substrate/Enzyme Combinations to Generate Antimicrobial Activity in situ

The last decade has witnessed a renewed interest in antimicrobial agents. Plants have received particular attention and frequently rely on the spontaneous enzymatic conversion of an inactive precursor to an active agent. Such two-component substrate/enzyme defence systems can be reconstituted ex vivo. Here, the alliin/alliinase system from garlic seems to be rather effective against Saccharomyces cerevisiae, whilst the glucosinolate/myrosinase system from mustard appears to be more active against certain bacteria. Studies with myrosinase also confirm that enzyme and substrate can be added sequentially. Ultimately, such binary systems hold considerable promise and may be employed in a medical or agricultural context.

Taste detection of the non-volatile isothiocyanate moringin results in deterrence to glucosinolate-adapted insect larvae

Isothiocyanates (ITCs), released from Brassicales plants after hydrolysis of glucosinolates, are known for their negative effects on herbivores but mechanisms have been elusive. The ITCs are initially present in dissolved form at the site of herbivore feeding, but volatile ITCs may subsequently enter the gas phase and all ITCs may react with matrix components. Deterrence to herbivores resulting from topically applied volatile ITCs in artificial feeding assays may hence lead to ambiguous conclusions. In the present study, the non-volatile ITC moringin (4-(α-L-rhamnopyranosyloxy)benzyl ITC) and its glucosinolate precursor glucomoringin were examined for effects on behaviour and taste physiology of specialist insect herbivores of Brassicales. In feeding bioassays, glucomoringin was not deterrent to larvae of Pieris napi (Lepidoptera: Pieridae) and Athalia rosae (Hymenoptera: Tenthredinidae), which are adapted to glucosinolates. Glucomoringin stimulated feeding of larvae of the related Pieris brassicae (Lepidoptera: Pieridae) and also elicited electrophysiological activity from a glucosinolate-sensitive gustatory neuron in the lateral maxillary taste sensilla. In contrast, the ITC moringin was deterrent to P. napi and P. brassicae at high levels and to A. rosae at both high and low levels when topically applied to cabbage leaf discs (either 12, 120 or 1200 nmol moringin per leaf disc of 1cm diameter). Survival of A. rosae was also significantly reduced when larvae were kept on leaves treated with moringin for several days. Furthermore, moringin elicited electrophysiological activity in a deterrent-sensitive neuron in the medial maxillary taste sensillum of P. brassicae, providing a sensory mechanism for the deterrence and the first known ITC taste response of an insect. In simulated feeding assays, recovery of moringin was high, in accordance with its non-volatile nature. Our results demonstrate taste-mediated deterrence of a non-volatile, natural ITC to glucosinolate-adapted insects.

Degradation of Biofumigant Isothiocyanates and Allyl Glucosinolate in Soil and Their Effects on the Microbial Community Composition

Brassicales species rich in glucosinolates are used for biofumigation, a process based on releasing enzymatically toxic isothiocyanates into the soil. These hydrolysis products are volatile and often reactive compounds. Moreover, glucosinolates can be degraded also without the presence of the hydrolytic enzyme myrosinase which might contribute to bioactive effects. Thus, in the present study the stability of Brassicaceae plant-derived and pure glucosinolates hydrolysis products was studied using three different soils (model biofumigation). In addition, the degradation of pure 2-propenyl glucosinolate was investigated with special regard to the formation of volatile breakdown products. Finally, the influence of pure glucosinolate degradation on the bacterial community composition was evaluated using denaturing gradient gel electrophoresis of 16S rRNA gene amplified from total community DNA. The model biofumigation study revealed that the structure of the hydrolysis products had a significant impact on their stability in the soil but not the soil type. Following the degradation of pure 2-propenyl glucosinolate in the soils, the nitrile as well as the isothiocyanate can be the main degradation products, depending on the soil type. Furthermore, the degradation was shown to be both chemically as well as biologically mediated as autoclaving reduced degradation. The nitrile was the major product of the chemical degradation and its formation increased with iron content of the soil. Additionally, the bacterial community composition was significantly affected by adding pure 2-propenyl glucosinolate, the effect being more pronounced than in treatments with myrosinase added to the glucosinolate. Therefore, glucosinolates can have a greater effect on soil bacterial community composition than their hydrolysis products.