Rocket salad (Diplotaxis and Eruca spp.) sensory analysis and relation with glucosinolate and phenolic content

Cyclic Isothiocyanate Goitrin Impairs Lotus japonicus Nodulation, Affects the Proteomes of Nodules and Free Mesorhizobium loti, and Induces the Formation of Caffeic Acid Derivatives in Bacterial Cultures

The continuous release of glucosinolates into the soil by Brassicaceae root exudation is a prerequisite to maintaining toxic levels of breakdown products such as isothiocyanates (ITCs). ITCs influence plant and microbial diversity in ecosystems, while fungi and Rhizobiaceae are particularly injured. Studies explaining the molecular mechanisms of the negative effects are presently limited. Therefore, we investigated the early effects of cyclic ITC goitrin on proteomes of the host and symbiotic Mesorhizobium loti in the nodules of Lotus japonicus and of free-living bacteria. In the nodules, many host proteins had a higher abundance, among them, peroxidases and pathogenesis-related PR-10 proteins functioning in the abscisic-acid-activated signaling pathway. In the microsymbiont, transporter proteins as a prominent group are enhanced; some proteins involved in N-fixation decreased. The proteomes give a report about the loss of immunity suppression resulting in the termination of symbiosis, which initiates nodule senescence. Free-living M. loti are severely damaged, indicated, i.a., by a decrease in transporter proteins, the assumed candidates for goitrin protein complex formation, and high proteolysis. The production of chicoric acid by the accompanying bacteria is inhibitory for M. loti but connected to goitrin elimination, as confirmed by mass spectrometric (MS) analysis. In summary, the nodulation process is severely affected by goitrin, causing nodule dysfunction and failed nodule development. N deficiency conditions leads to yellowish leaves and leaf abscission.

How do pretreatment and frozen storage impact the volatile profiles of Brussels sprouts and leek?

The volatile profiles of Brussels sprouts and leek, as affected by pretreatment combined with frozen storage were analyzed in the present work. The data revealed that, notwithstanding the effect upon pretreatment seemed to be major compared to the effect upon frozen storage, the latter was existent. Pretreatment yielded volatile compounds that could be associated with (bio)chemical reaction pathways in both vegetables. For frozen storage at -20 °C, the effect for leek appeared to be the largest for the blanched and raw samples, possibly due to a substantial amount of substrates present when frozen storage was initiated in this sample compared to the other samples. Those substrates were apparently more prone to be affected upon frozen storage. For Brussels sprouts, this observation was less outspoken. Remarkably, the abundance of markers in pretreated Brussels sprouts seemed to show a decreasing linear trend towards the end of the frozen storage period at -20 °C. As industrial relevant conditions were considered and compared, the insights gained in this study might be relevant to implement on industrial level.

Diplotaxis Genus: A Promising Source of Compounds with Nutritional and Biological Properties

Research on bioactive compounds is essential to improve human health; promote adequate nutrition; drive innovation in the food, agricultural and biotechnology industries; and contribute to the preservation of the environment. The genus Diplotaxis (Brassicaceae) currently comprises around forty species, some of which are edible, particularly Diplotaxis tenuifolia (wild rocket), Diplotaxis erucoides (wall rocket), Diplotaxis muralis (annual wall rocket), Diplotaxis viminea (perennial wall rocket), and Diplotaxis simplex. The leaves of these species are rich in fiber and essential minerals, such as calcium, iron, potassium, and magnesium. Thirteen species have been characterized for their phenolic compounds, predominantly kaempferol, quercetin, and isorhamnetin glycosides. Furthermore, glucosinolate compounds were identified in nineteen species of the genus Diplotaxis. Many of the phytochemicals identified in Diplotaxis spp. demonstrated interesting biological activities, such as antioxidant, anti-inflammatory, antibacterial, hypoglycemic and hypolipidemic effects, as well as cytotoxicity and antiproliferative properties. This article provides a review of the phytochemistry of the Diplotaxis genus, highlighting its importance in food, its biological properties, potential pharmacological applications, and the dearth of research on many of these plants.

Sensory Attributes Driving Preference for Wild Rocket (Diplotaxis tenuifolia) Leaves Tasted as a Single Ingredient and as a Part of a Recipe

Two cultivars of wild rocket (Diplotaxis tenuifolia), cv. Denver and Marte, were subjected to chemical determination of flavour-related constituents, sensory descriptive analysis, and measurement of liking by consumer test. Consumers evaluated rocket leaves both as a single ingredient and in a recipe formed by a roll of bresaola with also Grana Padano cheese. Sensory analyses showed that Marte was characterized by a more intense bitterness, hotness, and pungency, which corresponded to a higher total GSL content, mainly due to a higher level of dimeric 4-mercaptobutyl GSL. Five clusters of consumers were identified based on their liking scores. When tasting rocket leaves as a single ingredient, three clusters showed a higher liking for the milder cultivar, one cluster showed an opposite preference, while flavour attributes, such as bitterness and hotness, appeared as the main drivers of liking. Differences in liking were no longer found between the two cultivars when rocket leaves were evaluated in the recipe. Therefore, as rocket leaves are generally consumed as a part of a recipe with other ingredients instead of as a single ingredient, in the assessment of consumer preferences, it should not be neglected the influence of the way in which the product is consumed.

Metabolite Profiling for Typization of "Rucola della Piana del Sele" (PGI), Eruca sativa, through UHPLC-Q-Exactive-Orbitrap-MS/MS Analysis

In August 2020, the Eruca sativa cultivar "Rucola della Piana del Sele" obtained from the European Union the prestigious PGI (protected geographical indication) label, which certifies the uniqueness of its characteristics and increases its prestige both nationally and, above all, internationally. This plant is recognized as a product of excellence, with a unique flavor and unmistakable aroma. Therefore, since there are no methods to characterize the PGI product, a metabolomic approach was applied to characterize E. sativa grown in the Piana del Sele and different geographical areas. As E. sativa has very wide cultivation, this study sought to compare the metabolite profiles of rocket grown in Piana del Sele, Bergamo, and Brescia, as well as in Switzerland, making a comparison also with the metabolite profile of E. sativa grown spontaneously. To determine the best procedure to distinguish "Rucola della Piana del Sele" from the others, different extraction procedures were carried out using different solvents and fresh or freeze-dried plant matrices. The different extracts were analyzed by liquid chromatography coupled with high-resolution mass spectrometry experiments, using chemometric analyses to identify biomarker metabolites that characterize the PGI product. The LC-ESI-Q-Exactive-MS/MS profiles of methanol and hydroalcoholic extracts of different cultivars of E. sativa were found to be rich in bioactive compounds such as glucosinolates, glycosylated flavonoids, fatty acids, and lipids. The LCMS data were analyzed by principal component analysis (PCA); the score scatter plot shows significant separation among Eruca samples grown in different geographical areas. In detail, loading the scatter plot revealed Eruca grown in Piana del Sele to be richer than other cultivars in glycosylated quercetin 3,3',4'-O-triglucoside (7), quercetin-3,4'-O-diglucoside-3'-O-(6-sinapoyl-glucoside) (10), and quercetin diglucoside (30). Finally, considering the biological interest in erucin, the myrosinase product of glucoerucin, the latter was quantified in the extracts by LC-ESI/QTrap/MS/MS using the multiple reaction monitoring (MRM) method; E. sativa from Piana del Sele showed the highest content of glucoerucin.

Salt-Affected Rocket Plants as a Possible Source of Glucosinolates

Soil salinity can have various negative consequences on agricultural products, from their quality and production to their aesthetic traits. In this work, the possibility to use salt-affected vegetables, that otherwise would be discarded, as a source of nutraceuticals was explored. To this aim, rocket plants, a vegetable featuring bioactive compounds such as glucosinolates, were exposed to increasing NaCl concentrations in hydroponics and analysed for their content in bioactive compounds. Salt levels higher than 68 mM produced rocket plants that did not comply with European Union regulations and would therefore be considered a waste product. Anyway, our findings, obtained by Liquid Chromatography-High Resolution Mass Spectrometry, demonstrated a significant increase in glucosinolates levels in such salt-affected plants. opening the opportunity for a second life of these market discarded products to be recycled as glucosinolates source. Furthermore, an optimal situation was found at NaCl 34 mM in which not only were the aesthetic traits of rocket plants not affected, but also the plants revealed a significant enrichment in glucosinolates. This can be considered an advantageous situation in which the resulting vegetables still appealed to the market and showed improved nutraceutical aspects.

LED omics in Rocket Salad (Diplotaxis tenuifolia): Comparative Analysis in Different Light-Emitting Diode (LED) Spectrum and Energy Consumption

By applying three different LED light treatments, designated as blue (B), red (R)/blue (B), red (R) and white (W) light, as well as the control, the effect on Diplotaxis tenuifolia phenotype (yield and quality), and physiological, biochemical, and molecular status, as well as growing system resource use efficiency, was examined. We observed that basic leaf characteristics, such as leaf area, leaf number, relative chlorophyll content, as well as root characteristics, such as total root length and root architecture, remained unaffected by different LEDs. Yield expressed in fresh weight was slightly lower in LED lights than in the control (1113 g m^-2), with R light producing the least (679 g m^-2). However, total soluble solids were significantly affected (highest, 5.5° Brix, in R light) and FRAP was improved in all LED lights (highest, 191.8 μg/g FW, in B) in comparison to the control, while the nitrate content was less (lowest, 949.2 μg/g FW, in R). Differential gene expression showed that B LED light affected more genes in comparison to R and R/B lights. Although total phenolic content was improved under all LED lights (highest, 1.05 mg/g FW, in R/B), we did not detect a significant amount of DEGs in the phenylpropanoid pathway. R light positively impacts the expression of the genes encoding for photosynthesis components. On the other hand, the positive impact of R light on SSC was possibly due to the expression of key genes being induced, such as SUS1. In summary, this research is an integrative and innovative study, where the exploration of the effect of different LED lights on rocket growing under protected cultivation, in a closed chamber cultivation system, was performed at multiple levels.

Effects of Arugula Vermicompost on the Root-Knot Nematode (Meloidogyne javanica) and the Promotion of Resistance Genes in Tomato Plants

Root-knot nematodes are the most important plantparasitic nematodes worldwide. Many efforts have been made to find non-chemical, risk-free, and environmentally friendly methods for nematode control. In this study, the effects of compost and vermicompost of arugula (Eruca sativa) on Meloidogyne javanica were investigated in three glasshouse experiments. In addition, the expression of the defense-related genes nonexpressor of pathogenesis-related 1 (NPR1) and lipoxygenase 1 (LOX1) was detected in tomato plants treated with vermicompost of arugula at 0, 2, 7, and 14 days after nematode inoculation. The result showed that the vermicompost of arugula significantly reduced the reproduction factor of the nematode by 54.4% to 70.5% in the three experiments and increased the dry weight of shoots of infected tomato plants. Gene expression analysis showed that LOX1 expression increased on the second and seventh day after nematode inoculation, while NPR1 expression decreased. The vermicompost of arugula showed stronger nematode inhibitory potential than the vermicompost of animal manure. The vermicompost of arugula is superior to arugula compost in suppressing the activity of M. javaniva and reducing its impact. It manipulates the expression of resistance genes and could induce systemic resistance against rootknot nematodes.

Flavour Generation during Lactic Acid Fermentation of Brassica Vegetables—Literature Review

Fermentation is a method of food preservation that has been used for centuries. Lactic acid fermentation, apart from extending the shelf-life of vegetables, affects significantly the flavour of food products. In this review, the formation of flavour, including both taste and aroma, in fermented Brassica vegetables is summarized. The flavour-active compounds are generated in various metabolic pathways from many precursors present in raw materials used for fermentation. In Brassica vegetables, a unique group of chemicals, namely glucosinolates, is present, which significantly influence the flavour of fermented products. In this summary, we took a closer look at the flavour of two of the most commonly eaten worldwide fermented Brassica products, which are sauerkraut and kimchi. Finally, the needs and directions for future studies were addressed.

Surveying soil-borne disease development on wild rocket salad crop by proximal sensing based on high-resolution hyperspectral features

Wild rocket (Diplotaxis tenuifolia, Brassicaceae) is a baby-leaf vegetable crop of high economic interest, used in ready-to-eat minimally processed salads, with an appreciated taste and nutraceutical features. Disease management is key to achieving the sustainability of the entire production chain in intensive systems, where synthetic fungicides are limited or not permitted. In this context, soil-borne pathologies, much feared by growers, are becoming a real emergency. Digital screening of green beds can be implemented in order to optimize the use of sustainable means. The current study used a high-resolution hyperspectral array (spectroscopy at 350-2500 nm) to attempt to follow the progression of symptoms of Rhizoctonia, Sclerotinia, and Sclerotium disease across four different severity levels. A Random Forest machine learning model reduced dimensions of the training big dataset allowing to compute de novo vegetation indices specifically informative about canopy decay caused by all basal pathogenic attacks. Their transferability was also tested on the canopy dataset, which was useful for assessing the health status of wild rocket plants. Indeed, the progression of symptoms associated with soil-borne pathogens is closely related to the reduction of leaf absorbance of the canopy in certain ranges of visible and shortwave infrared spectral regions sensitive to reduction of chlorophyll and other pigments as well as to modifications of water content and turgor.

Identification of sensory properties driving consumers' liking of commercially available kale and arugula

BACKGROUND

Kale and arugula are leafy green vegetables whose sensory properties have not been extensively explored. The objective was to assess the sensory properties and consumer acceptability of commercially available kale and arugula while also discovering drivers of consumer liking and barriers to consumer acceptance. Descriptive analysis and consumer testing were completed. The trained panellists (n = 11) were trained for 15 h to evaluate 11 sensory properties relating to the aroma, taste and texture of the kale and arugula. The consumer testing (n = 108) evaluated the leafy greens for overall liking and their liking of taste, aroma, texture and appearance.

RESULTS

Results were analyzed using ANOVA, Tukey's HSD and external preference mapping. Approximately half of the attributes for the kale samples were found to be significantly different. Similarly, significant differences in sensory properties were found in most of the arugula samples. Consumers liked the kale and arugula varieties that were sweet and nutty. Also, they preferred arugula that was described as spicy.

CONCLUSION

The majority of consumers preferred sweet and nutty leafy greens. Organic growing methods did not affect consumer liking; however, organic labels do positively affect hedonic ratings of a consumer's overall liking of the product. This study also identified that 'Baby' leafy greens are well liked by consumers, and this area of produce should be expanded. © 2021 Society of Chemical Industry.

High Glucosinolate Content in Rocket Leaves (Diplotaxis tenuifolia and Eruca sativa) after Multiple Harvests Is Associated with Increased Bitterness, Pungency, and Reduced Consumer Liking

Rocket (Diplotaxis tenuifolia and Eruca sativa) leaves delivered to the UK market are variable in appearance, taste, and flavour over the growing season. This study presents sensory and consumer analyses of rocket produce delivered to the UK over the course of one year, and evaluated the contribution of environmental and cultivation factors upon quality traits and phytochemicals called glucosinolates (GSLs). GSL abundance was positively correlated with higher average growth temperatures during the crop cycle, and perceptions of pepperiness, bitterness, and hotness. This in turn was associated with reduced liking, and corresponded to low consumer acceptance. Conversely, leaves with greater sugar content were perceived as more sweet, and had a higher correlation with consumer acceptance of the test panel. First cut leaves of rocket were favoured more by consumers, with multiple leaf cuts associated with low acceptance and higher glucosinolate concentrations. Our data suggest that the practice of harvesting rocket crops multiple times reduces consumer acceptability due to increases in GSLs, and the associated bitter, hot, and peppery perceptions some of their hydrolysis products produce. This may have significant implications for cultivation practices during seasonal transitions, where leaves typically receive multiple harvests and longer growth cycles.

The Relationship between Glucosinolates and the Sensory Characteristics of Steamed-Pureed Turnip (Brassica Rapa subsp. Rapa L.)

Glucosinolates (GSLs) are phytochemical compounds that can be found in Brassica vegetables. Seven separate batches of steamed-pureed turnip were assessed for GSL content using liquid chromatography mass spectrometry (LC-MS) and for sensory attributes by sensory profiling (carried out by a trained sensory panel). Twelve individual GSLs, which included 7 aliphatic, 4 indole and 1 arylaliphatic GSL, were identified across all batches. There were significant differences in individual GSL content between batches, with gluconasturtiin as the most abundant GSL. The total GSL content ranged from 16.07 to 44.74 μmol g^-1 dry weight (DW). Sensory profiling concluded there were positive correlations between GSLs and bitter taste and negative correlations between GSLs (except glucobrassicanapin) and sweet taste. The batches, which had been purchased across different seasons, all led to cooked turnip that contained substantial levels of GSLs which were subsequently all rated as bitter.

Red Light Is Effective in Reducing Nitrate Concentration in Rocket by Increasing Nitrate Reductase Activity, and Contributes to Increased Total Glucosinolates Content

Rocket cultivation is increasing to supply the expanding ready-to-eat market because of its unique taste, but crops are often over fertilized to avoid nitrogen deficiencies. This leads to nitrate accumulation in leaves, and the products of their degradation (nitrites and nitrosamines) have been related to several health problems. Nitrate concentrations in rocket and other leafy vegetables are subject to limits by the EU legislation, yet rocket holds a great nutritional value. Degradation products of glucosinolates (isothiocyanates) have been consistently linked with benefits to human health. We investigated the influence of nitrogen application (1 and 8 mM), species [Eruca sativa (L.) Cav. and Diplotaxis tenuifolia (L.) DC.] and light spectrum (full spectrum, red, blue and red + blue) on the nitrate concentration, nitrate reductase activity and glucosinolate content of rocket grown in a soil-less system. Red light decreased the nitrate concentration with respect to the blue spectrum (4,270 vs. 7,100 mg⋅kg-1 of fresh weight, respectively), but such reduction was influenced by the species and the nitrogen level (significantly higher in D. tenuifolia and with the higher concentration of N). The nitrate reductase activity increased under red light in D. tenuifolia, with the lower N concentration. Rocket is known to contain several health-promoting compounds mainly antioxidants and glucosinolates, as secondary metabolites that act as part of plant defense mechanisms. The total content of glucosinolates was mainly affected by the species (D. tenuifolia showed the highest concentrations). Our results will help growers to tailor light spectra with the aim of reducing nitrate concentration and to remain within EU legislative limits, without any detrimental influence on other qualitative parameters in rocket.

Growth temperature influences postharvest glucosinolate concentrations and hydrolysis product formation in first and second cuts of rocket salad

Rocket salad species (Diplotaxis tenuifolia and Eruca sativa; also known as E. vesicaria) are known for their high concentrations of health-related isothiocyanates, which are derived from secondary metabolites called glucosinolates. Increases in temperature due to climate change and extreme weather event frequencies over the coming decades are likely to influence not only the growth of leafy vegetables, but also their nutritional density. It is therefore essential to determine the impacts of these in order to mitigate crop losses and nutritional decline in future. Our data show there is a strong influence of pre-harvest growth temperatures on glucosinolate biosynthesis and formation of glucosinolate hydrolysis products postharvest, and that this is genotype dependent. High growth temperature (40 °C) severely retarded germination, growth, regrowth, and survival of rocket plants. Highest glucosinolate concentrations were observed in first and second cuts at 40 °C, but did not correspond to highest isothiocyanate concentrations (observed at 30 °C, second cut). Hydrolysis product formation is proportionately not as great as glucosinolate increases at 40 °C, possibly due to inhibition of enzyme function(s) at higher temperatures. These data indicate that high growth temperatures increase glucosinolate accumulation, but growth and productivity is significantly reduced. Much greater emphasis is needed for breeding cultivars tolerant to high growth temperatures in order to maximise nutritional benefits imparted by temperature stress.

Consumers acceptance and volatile profile of wall rocket (Diplotaxis erucoides)

Wall rocket (Diplotaxis erucoides) is a wild edible herb traditionally consumed in the Mediterranean regions with a characteristic, pungent flavour. However, little is known about its acceptance as a potential new crop. In the present study, an hedonic test with 98 volunteers was performed in order to evaluate the potential of wall rocket as a new crop. Three products were tested corresponding to microgreens, seedlings and baby-leaves. The volatile constituents were also studied due to their probable influence on acceptance, and compared to Dijon's mustard and wasabi. The degree of acceptance was mainly related to taste and pungency. Microgreens were well accepted, whereas seedlings and baby-leaves were mainly appreciated by individuals that enjoy pungent tastes. The purchase intent was also highly related to the acceptance of taste and pungency. The volatiles profile revealed that wall rocket was rich in allyl isothiocyanate, like mustard and wasabi. This compound may be greatly responsible of the relationship between the acceptance of mustard, wasabi and wall rocket. Microgreens displayed the highest levels of isothiocyanates, although the quantity of product tested by panellists did not probably allow the appreciation of such compounds. In baby-leaves, a significant decrease in isothiocyanates GC area and relative abundances was observed. These results suggest that wall rocket microgreens would be accepted by a significant proportion of the general public since pungency is lowly perceived in the product, despite its high levels of isothiocyanates. By contrast, baby-leaves may become a crop for a cohort of consumers that enjoy pungent flavours.

Glucosinolate structural diversity, identification, chemical synthesis and metabolism in plants

The glucosinolates (GSLs) is a well-defined group of plant metabolites characterized by having an S-β-d-glucopyrano unit anomerically connected to an O-sulfated (Z)-thiohydroximate function. After enzymatic hydrolysis, the sulfated aglucone can undergo rearrangement to an isothiocyanate, or form a nitrile or other products. The number of GSLs known from plants, satisfactorily characterized by modern spectroscopic methods (NMR and MS) by mid-2018, is 88. In addition, a group of partially characterized structures with highly variable evidence counts for approximately a further 49. This means that the total number of characterized GSLs from plants is somewhere between 88 and 137. The diversity of GSLs in plants is critically reviewed here, resulting in significant discrepancies with previous reviews. In general, the well-characterized GSLs show resemblance to C-skeletons of the amino acids Ala, Val, Leu, Trp, Ile, Phe/Tyr and Met, or to homologs of Ile, Phe/Tyr or Met. Insufficiently characterized, still hypothetic GSLs include straight-chain alkyl GSLs and chain-elongated GSLs derived from Leu. Additional reports (since 2011) of insufficiently characterized GSLs are reviewed. Usually the crucial missing information is correctly interpreted NMR, which is the most effective tool for GSL identification. Hence, modern use of NMR for GSL identification is also reviewed and exemplified. Apart from isolation, GSLs may be obtained by organic synthesis, allowing isotopically labeled GSLs and any kind of side chain. Enzymatic turnover of GSLs in plants depends on a considerable number of enzymes and other protein factors and furthermore depends on GSL structure. Identification of GSLs must be presented transparently and live up to standard requirements in natural product chemistry. Unfortunately, many recent reports fail in these respects, including reports based on chromatography hyphenated to MS. In particular, the possibility of isomers and isobaric structures is frequently ignored. Recent reports are re-evaluated and interpreted as evidence of the existence of "isoGSLs", i.e. non-GSL isomers of GSLs in plants. For GSL analysis, also with MS-detection, we stress the importance of using authentic standards.

Glucosinolate Content and Sensory Evaluation of Baby Leaf Rapeseed from Annual and Biennial White- and Yellow-Flowering Cultivars with Repeated Harvesting in Two Seasons

The chemical and sensory quality of field-grown vegetables may be influenced by cultivar choice and agronomic factors but knowledge is lacking on the new rapeseed vegetables. White- and yellow-flowering rapeseed cultivars were tested in two seasonally different field studies in Denmark at three different growing stages by early sowing the first year and late sowing the second year. Content of glucosinolates (GLSs) was analyzed, and the sensory quality of baby leaf samples was evaluated. The GLS content differed among cultivars across years in all growing stages, with biennial cultivars having the highest GLS content. In the second year, a higher content of all identified GLSs was found at two growing stages except for neoglucobrassicin and gluconasturtiin, compared to the first year. On the contrary, higher contents of all identified GLSs were found at a third stage in the first year except for progoitrin and 4-methoxy glucobrassicin. Sensory evaluation of bitterness revealed differences among cultivars, higher intensities of bitterness in biennial cultivars, and a relationship between bitterness and content of bitter-tasting and total GLSs. The effect of repeated harvesting on GLS content differed between the years and no general pattern was seen, except that the composition of individual GLSs was comparable for the biennial cultivars. We conclude that growing season and life cycle had a stronger influence on GLS content than stage at harvest. The link between bitter-tasting GLSs and bitterness revealed that life cycle and seasonal effects affected the sensory profile of baby leaf rapeseed thereby making a healthier product due to high content of health-beneficial GLSs.

Influences of Psychological Traits and PROP Taster Status on Familiarity with and Choice of Phenol-Rich Foods and Beverages

Plant phenolics are powerful antioxidants and free radical scavengers that can contribute to the healthy functional properties of plant-based food and beverages. Thus, dietary behaviours rich in plant-based food and beverages are encouraged. However, it is well-known that the bitter taste and other low-appealing sensory properties that characterize vegetables and some other plant-based foods act as an innate barrier for their acceptance. The aim of this study was to investigate the influence of psychological traits and PROP status (the responsiveness to bitter taste of 6-n- propylthiouracil) on the choice of and familiarity with phenol-rich vegetables and beverages varying in recalled level of bitterness and astringency. Study 1 aimed at assessing the variations of the sensory properties of vegetable and coffee/tea items with two check-all-that-apply (CATA) questionnaires (n = 201 and n = 188 individuals, respectively). Study 2 aimed at investigating how sensitivity to punishment, to reward, and to disgust, food neophobia, private body consciousness, alexithymia, and PROP responsiveness affect choice and familiarity with phenol-rich foods (n = 1200 individuals). A Choice Index was calculated for vegetables (CV) and coffee/tea (CC) as a mean of the choices of the more bitter/astringent option of the pairs and four Familiarity Indices were computed for vegetables (FV) and coffee/tea (FC), higher (+) or lower (-) in bitterness and astringency. Subjects higher in food neophobia, sensitivity to punishment or sensitivity to disgust reported significantly lower choice indices than individuals lower in these traits, meaning that they systematically opted for the least bitter/astringent option within the pairs. Familiarity with vegetables was lower in individuals high in sensitivity to punishment, in food neophobia and in alexithymia, irrespective of their sensory properties. The Familiarity Index with coffee/tea characterized by higher bitterness and astringency was lower in individuals high in food neophobia, sensitivity to disgust, and alexithymia. No significant effect of PROP was found on any indices. The proposed approach based on product grouping according to differences in bitterness and astringency allowed the investigation of the role of individual differences in chemosensory perception and of psychological traits as modulators of phenol-rich foods preference and consumption.

Rocket science: A review of phytochemical & health-related research in Eruca & Diplotaxis species

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Recent phytochemical research in rocket species is critically reviewed.

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Glucosinolates and hydrolysis products change over growth and shelf life.

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Experiments should better consider and account for commercial practices.

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Research should be focused on providing benefits to the end consumer.

Rocket species (Eruca spp. and Diplotaxis spp.) are becoming increasingly important leafy salad crops across the world. Numerous scientific research papers have been published in recent years surrounding the potential health benefits associated with phytochemicals contained in leaves, such as flavonoids and isothiocyanates. Other research of note has also been conducted into the unique taste and flavour properties of leaves, which can be hot, peppery, bitter, and sweet depending upon the genotype and phytochemical composition. While research into these aspects is increasing, some studies lack cohesion and in-depth knowledge of commercial breeding and cultivation practices that makes interpretation and application of results difficult. This review draws together all significant research findings in these crops over the last five years, and highlights areas that require further exploration and/or resolution. We also advise on experimental considerations for these species to allow for more meaningful utilisation of findings in the commercial sector.

Supercritical CO₂ Extraction of Eruca sativa Using Cosolvents: Phytochemical Composition by LC-MS Analysis

Background: Eruca sativa Mill. is a good source of glucosinolates (GLS), phenolic compounds and unsaturated fatty acids, being a valuable material for the production of functional-foods or nutraceutical ingredients. Extraction by supercritical CO₂ (SCO₂) can be used and the limitations due to the apolar nature of CO₂ can be overcome using co-solvents. In this paper different cosolvents and conditions were used for SCO₂ extraction and the composition of the obtained extracts was studied by LC-MS. Results: Water resulted the ideal co-solvent, allowing the extraction of glucosinolates in comparable amounts to the classical procedure with boiling water, as it can be carried out at mild temperatures (45 °C vs. >100 °C). Increasing the pressure improved the GLS extraction. On the other hand polyphenol extraction under the studied conditions was not influenced by pressure and temperature variations. The in vitro antioxidant effect of the obtained extracts was also measured, showing significant activity in the DPPH and FC tests. Conclusions: The GLS, flavonoids and lipids composition of the obtained extracts was studied, showing the presence of numerous antioxidant constituents useful for nutraceutical applications. The extraction method using SCO₂ and water as co-solvent presents advantages in terms of safety because these solvents are generally recognised as safe. Water as cosolvent at 8% resulted useful for the extraction of both glucosinolates and phenolics in good amount and is environmentally acceptable as well as safe for food production.

Effect of heat root stress and high salinity on glucosinolates metabolism in wild rocket

Wild rocket (Diplotaxis tenuifolia L.) is a leafy vegetable appreciated for its characteristic sensory properties which are mainly due to the presence of glucosinolates (GSLs). Short-term exposure to abiotic stresses can induce physiological responses and transcriptional changes which involve GSLs. For this reason, the aim of this work was to study the mechanisms of regulation of GSLs metabolism in rocket subjected to heat stress (40 °C) and high salinity (200 mM NaCl) imposed for up to 48 h. GSLs levels and the expression of methylthioalkylmalate synthase1 (DtMAM1), cytochromeP79F1 (DtCYP79F1), cytochromeP45083A1 (DtCYP83A1), cytosolic-sulfotransferase5b (DtST5b), cytosolic-sulfotransferase5c (DtST5c), flavinmono-oxygenase (DtFMO), myrosinase (DtMyro) and thio-methyl transferase (DtTMT) were analyzed under stress conditions. In addition, the effect on chlorophyll and glucose levels, as well as on chlorophyll a fluorescence were evaluated. Chlorophyll and chlorophyll fluorescence were not affected by the short-term application of stresses. Glucose levels in roots were doubled in response to high salinity, while, in the same organ, GSLs were three fold lower in response to both stresses. The relative content of several aliphatic GSLs was significantly reduced in leaves as a response to both stresses. A key role in GSLs metabolism and in the response to salinity is hypothesized for the gene DtTMT, as it showed an increment in transcripts accumulation (three-fold) consistent with the decrement in the GSLs levels found in salt-exposed leaves and roots. The results obtained in this study can be used in breeding programmes aiming to enhance rocket sensory quality and to improve the resistance to abiotic stresses.

Taste and Flavor Perceptions of Glucosinolates, Isothiocyanates, and Related Compounds

Brassicaceae plants are renowned for their taste, aroma and trigeminal characteristics; predominantly bitter taste, sulfurous aroma, and pungency. Compounds responsible for these sensations include the glucosinolates (GSLs) and their hydrolysis products, particularly isothiocyanates (ITCs), but also sulfur-containing volatile compounds. This article reviews the relative importance of taste and flavor perceptions resulting from such compounds; collating evidence from papers where findings are based on sensory analytical correlations, and those that have extracted specific compounds prior to sensory evaluation. Where specific GSLs impart bitterness and many ITCs impart pungency, this is clearly not true for all GSLs and ITCs. Designing crop improvement strategies for sensory traits based on total GSL content would be flawed, as it does not consider the relative differences in sensory characteristics of different GSLs and ITCs, nor the contribution from other GSL hydrolysis products. In addition, some Brassicaceae plants are consumed raw, whilst others are cooked; this affects not only the hydrolysis of GSLs, but also the generation and release of sulfides. Therefore, in breeding new plant varieties, it is prudent to consider the individual GSLs, the typical cooking conditions the plant is subjected to, enzyme stability, and resultant composition of both GSL hydrolysis products (including ITCs) and sulfides.

Quantitative and Qualitative Analysis of Eruca sativa and Brassica juncea Seeds by UPLC-DAD and UPLC-ESI-QTOF

Eruca sativa and Brassica juncea belong to the Brassicaceae family and have been used traditionally for the treatment of cancer and various cardiovascular ailments. A rapid and simple ultra performance liquid chromatography (UPLC) method has been developed for the simultaneous quantification of erucin, allyl isothiocyanate and benzyl isothiocyanate in E. sativa and B. juncea oil. Eruca sativa oil contains erucin (28.93%), allyl isothiocyanate (0.06%) and benzyl isothiocyanate (0.70%). Identification of other secondary metabolites in E. sativa and B. juncea oil and aqueous methanolic extracts were also carried out using ultra performance liquid chromatography-electro spray ionization-quadrupole time of flight (UPLC-ESI-QTOF). The UPLC-ESI-QTOF based study leads to the identification of ten compounds in B. juncea oil and three compounds in E. sativa oil. The UPLC-ESI-QTOF analysis of aqueous methanolic extracts of E. sativa and B. juncea leads to the identification of eight and nine compounds, respectively.

Effect of modified atmosphere packaging and temperature abuse on flavor related volatile compounds of rocket leaves (Diplotaxis tenuifolia L.)

The effect of storage conditions on flavor-related volatile composition of wild rocket (Diplotaxis tenuifolia) was investigated on Modified Atmosphere packed (MAP) leaves stored under isothermal and non-isothermal conditions. In a first experiment the effect of MAP was compared to the storage in air at 5 °C; a second experiment aimed to study the effect of non isothermal conditions, with two temperature abuses (at 13 °C for 24 h) during a 5 °C. Twenty-four volatiles were detected, including C6, C5, isothiocyanate, lipid-derived and sulfur compounds. In the first experiment, MAP-stored rocket showed a slower loss of typical flavour volatiles (thiocyanates and isothiocyanates) and a slower production of off-flavors until 6 days of storage, compared to leaves stored in air. After this time, dimethyl sulfide and acetaldehyde dramatically increased in MAP-stored rocket samples. In the second experiment, samples stored under non-isothermal conditions showed lower O₂ and higher CO₂ concentrations than samples stored under isothermal conditions. Rocket leaves stored under non-isothermal conditions showed an increased production of volatiles responsible of off-flavors (acetaldehyde and dimethyl sulfide) following temperature abuse comparing to storage in isothermal condition. Thus, dimethyl sulfide and acetaldehyde could be effective markers for tracking the effect of temperature fluctuations on rocket during storage.

Nutritional, Biophysical and Physiological Characteristics of Wild Rocket Genotypes As Affected by Soilless Cultivation System, Salinity Level of Nutrient Solution and Growing Period

With the aim of defining the best management of nutrient solution (NS) in a soilless system for obtaining high quality baby-leaf rocket, the present study focuses on two wild rocket genotypes ("Nature" and "Naturelle"), grown in a greenhouse under two Southern Italy growing conditions-autumn-winter (AW) and winter-spring (WS)-using two soilless cultivation systems (SCS)-at two electrical conductivity values (EC) of NS. The SCSs used were the Floating System (FS) and Ebb and Flow System (EFS) and the EC values were 2.5 and 3.5 dS m-1 (EC2.5; EC3.5) for the AW cycle and 3.5 and 4.5 dS m-1 (EC3.5; EC4.5) for the WS cycle. The yield, bio-physical, physiological and nutritional characteristics were evaluated. Higher fresh (FY) (2.25 vs. 1.50 kg m-2) and dry (DY) (230.6 vs. 106.1 g m-2) weight yield, leaf firmness (dry matter, 104.3 vs. 83.2 g kg-1 FW; specific leaf area, 34.8 vs. 24.2 g cm-2) and antioxidant compounds (vitamin C, 239.0 vs. 152.7 mg kg-1 FW; total phenols, 997 vs. 450 mg GAE mg kg-1 FW; total glucosinulates-GLSs, 1,078.8 vs. 405.7 mg kg-1 DW; total antioxidant capacity-TAC, 11,534 vs. 8,637 μmol eq trolox kg-1 FW) and lower nitrates (1,470 vs. 3,460 mg kg-1 FW) were obtained under WS conditions. The seasonal differences were evident on the GLS profile: some aliphatic GLSs (gluconapoleiferin, glucobrassicanapin) and indolic 4-OH-glucobrassicin were only expressed in WS conditions, while indolic glucobrassicin was only detected in the AW period. Compared with EFS, FS improved leaf firmness, visual quality, antioxidant content (TAC, +11.6%) and reduced nitrate leaf accumulation (-37%). "Naturelle" performed better than "Nature" in terms of yield, visual quality and nutritional profile, with differences more evident under less favorable climatic conditions and when the cultivars were grown in FS. Compared to EC2.5, the EC3.5 treatment did not affect DY while enhancing firmness, visual quality, and antioxidant compounds (TAC, +8%), and reducing the nitrate content (-47%). The EC4.5 treatment reduced FY and DY and the antioxidant content. Despite seasonal climatic condition variability, FS and the moderate salinity level of NS (3.5 dS m-1) can be suggested as optimum.

The influence of phytochemical composition and resulting sensory attributes on preference for salad rocket (Eruca sativa) accessions by consumers of varying TAS2R38 diplotype

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TAS2R38 bitterness perception does not wholly determine liking of rocket.

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Hotness is the main attribute on which consumers base their liking not bitterness.

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Some consumers prefer mild sweet accessions low in glucosinolates and pungent VOCs.

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Glucoraphanin imparts no significant influence on liking or sensory perceptions.

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Sugar-glucosinolate/isothiocyanate ratios are important for hotness perceptions.

Seven accessions of Eruca sativa (“salad rocket”) were subjected to a randomised consumer assessment. Liking of appearance and taste attributes were analysed, as well as perceptions of bitterness, hotness, pepperiness and sweetness. Consumers were genotyped for TAS2R38 status to determine if liking is influenced by perception of bitter compounds such as glucosinolates (GSLs) and isothiocyanates (ITCs). Responses were combined with previously published data relating to phytochemical content and sensory data in Principal Component Analysis to determine compounds influencing liking/perceptions. Hotness, not bitterness, is the main attribute on which consumers base their liking of rocket. Some consumers rejected rocket based on GSL/ITC concentrations, whereas some preferred hotness. Bitter perception did not significantly influence liking of accessions, despite PAV/PAV ‘supertasters’ scoring higher for this attribute. High sugar-GSL/ITC ratios significantly reduce perceptions of hotness and bitterness for some consumers. Importantly the GSL glucoraphanin does not impart significant influence on liking or perception traits.

Chemical composition and biological activities of Eruca vesicaria subsp. longirostris essential oils

Context To date, there are no reports to validate the Tunisian traditional and folklore claims of Eruca vesicaria (L) Cav. subsp. longirostris (Brassicaceae) for the treatment of disease. Objective Investigation of the chemical composition antimicrobial and antioxidant activity of essential oils from Eruca longirostris leaves, stems, roots and fruits. Materials and methods The essential oils of E. longirostris from leaves, stems, roots and fruits were obtained after 4 h of hydrodistillation. Chemical compositions were determined using a combination of GC/FID and GC/MS. The in vitro antimicrobial activity of the volatile constituents of E. longirostris was performed in sterile 96-well microplates against three Gram-positive, four Gram-negative bacteria and one strain as yeast. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration values were reported. Furthermore, the antioxidant activity was evaluated by DPPH and ABTS assays. Results The main compound for fruits, stems and roots was the erucin (96.6%, 85.3% and 83.7%, respectively), while β-elemene (35.7%), hexahydrofarnesylacetone (23.9%), (E)-β-damascone (15.4%), erucin (10.6%) and α-longipinene (9.6%) constituted the major compounds in the essential oil of the leaves. The experimental results showed that in all tests, essential oil of fruits showed the better antioxidant activity than the others. On the other hand, the oils of stems, fruits and roots showed significant antimicrobial activity with MIC values ranging from 0.125 to 0.31 mg/mL against Candida species, Gram-positive and Gram-negative bacteria, mainly Salmonella enterica. Conclusions The present results indicate that essential oils of E. longirostris can be used as a source of erucin.

Analysis of seven salad rocket (Eruca sativa) accessions: The relationships between sensory attributes and volatile and non-volatile compounds

Sensory and chemical analyses were performed on accessions of rocket (Eruca sativa) to determine phytochemical influences on sensory attributes. A trained panel was used to evaluate leaves, and chemical data were obtained for polyatomic ions, amino acids, sugars and organic acids. These chemical data (and data of glucosinolates, flavonols and headspace volatiles previously reported) were used in Principal Component Analysis (PCA) to determine variables statistically important to sensory traits. Significant differences were observed between samples for polyatomic ion and amino acid concentrations. PCA revealed strong, positive correlations between glucosinolates, isothiocyanates and sulfur compounds with bitterness, mustard, peppery, warming and initial heat mouthfeel traits. The ratio between glucosinolates and sugars inferred reduced perception of bitter aftereffects. We highlight the diversity of E. sativa accessions from a sensory and phytochemical standpoint, and the potential for breeders to create varieties that are nutritionally and sensorially superior to existing ones.

Leaf Metabolic, Genetic, and Morphophysiological Profiles of Cultivated and Wild Rocket Salad (Eruca and Diplotaxis Spp.)

Rocket salad (Diplotaxis spp., Eruca spp.) is a leafy vegetable rich in health-promoting compounds and widely consumed. In the present study, metabolic profiles of 40 rocket accessions mainly retrieved from gene banks were assessed. Seven glucosinolates (GLSs) and 15 flavonol compounds were detected across genotypes. Dimeric 4-mercaptobutyl-GLS and 4-(β-d-glucopyranosyldisulfanyl)butyl-GLS were the major components of the total glucosinolate content. Flavonols were different between genera, with the exception of isorhamnetin 3,4'-diglucoside. Morphoagronomic traits and color coordinates were also scored. Results showed a negative correlation between color and GLSs, indicating these last as responsible for the increase of the intensity of green and yellow pigments as well as for the darkness of the leaf, whereas agronomic traits showed positive correlation with GLSs. Genetic diversity was assessed using inter simple sequence repeat (ISSR) markers, allowing separation of the accessions on the basis of the species and elucidating the observations made by means of phenotypic data.

Food Processing and the Mediterranean Diet

The benefits of the Mediterranean diet (MD) for protecting against chronic disorders such as cardiovascular disease are usually attributed to high consumption of certain food groups such as vegetables, and low consumption of other food groups such as meat. The influence of food processing techniques such as food preparation and cooking on the nutrient composition and nutritional value of these foods is not generally taken into consideration. In this narrative review, we consider the mechanistic and epidemiological evidence that food processing influences phytochemicals in selected food groups in the MD (olives, olive oil, vegetables and nuts), and that this influences the protective effects of these foods against chronic diseases associated with inflammation. We also examine how the pro-inflammatory properties of meat consumption can be modified by Mediterranean cuisine. We conclude by discussing whether food processing should be given greater consideration, both when recommending a MD to the consumer and when evaluating its health properties.

A novel role of Eruca sativa Mill. (rocket) extract: antiplatelet (NF-κB inhibition) and antithrombotic activities

Background: Epidemiological studies have shown the prevention of cardiovascular diseases through the regular consumption of vegetables. Eruca sativa Mill., commonly known as rocket, is a leafy vegetable that has anti-inflammatory activity. However, its antiplatelet and antithrombotic activities have not been described. Methods: Eruca sativa Mill. aqueous extract (0.1 to 1 mg/mL), was evaluated on human platelets: (i) P-selectin expression by flow cytometry; (ii) platelet aggregation induced by ADP, collagen and arachidonic acid; (iii) IL-1β, TGF-β1, CCL5 and thromboxane B2 release; and (iv) activation of NF-κB and PKA by western blot. Furthermore, (v) antithrombotic activity (200 mg/kg) and (vi) bleeding time in murine models were evaluated. Results: Eruca sativa Mill. aqueous extract (0.1 to 1 mg/mL) inhibited P-selectin expression and platelet aggregation induced by ADP. The release of platelet inflammatory mediators (IL-1β, TGF-β1, CCL5 and thromboxane B2) induced by ADP was inhibited by Eruca sativa Mill. aqueous extract. Furthermore, Eruca sativa Mill. aqueous extract inhibited NF-κB activation. Finally, in murine models, Eruca sativa Mill. aqueous extract showed significant antithrombotic activity and a slight effect on bleeding time. Conclusion: Eruca sativa Mill. presents antiplatelet and antithrombotic activity.

Identification and quantification of glucosinolate and flavonol compounds in rocket salad (Eruca sativa, Eruca vesicaria and Diplotaxis tenuifolia) by LC-MS: highlighting the potential for improving nutritional value of rocket crops

Liquid chromatography mass spectrometry (LC-MS) was used to obtain glucosinolate and flavonol content for 35 rocket accessions and commercial varieties. 13 glucosinolates and 11 flavonol compounds were identified. Semi-quantitative methods were used to estimate concentrations of both groups of compounds. Minor glucosinolate composition was found to be different between accessions; concentrations varied significantly. Flavonols showed differentiation between genera, with Diplotaxis accumulating quercetin glucosides and Eruca accumulating kaempferol glucosides. Several compounds were detected in each genus that have only previously been reported in the other. We highlight how knowledge of phytochemical content and concentration can be used to breed new, nutritionally superior varieties. We also demonstrate the effects of controlled environment conditions on the accumulations of glucosinolates and flavonols and explore the reasons for differences with previous studies. We stress the importance of consistent experimental design between research groups to effectively compare and contrast results.

Elicitation: a tool for enriching the bioactive composition of foods

Elicitation is a good strategy to induce physiological changes and stimulate defense or stress-induced responses in plants. The elicitor treatments trigger the synthesis of phytochemical compounds in fruits, vegetables and herbs. These metabolites have been widely investigated as bioactive compounds responsible of plant cell adaptation to the environment, specific organoleptic properties of foods, and protective effects in human cells against oxidative processes in the development of neurodegenerative and cardiovascular diseases and certain types of cancer. Biotic (biological origin), abiotic (chemical or physical origin) elicitors and phytohormones have been applied alone or in combinations, in hydroponic solutions or sprays, and in different selected time points of the plant growth or during post-harvest. Understanding how plant tissues and their specific secondary metabolic pathways respond to specific treatments with elicitors would be the basis for designing protocols to enhance the production of secondary metabolites, in order to produce quality and healthy fresh foods.

Glucosinolates, myrosinase hydrolysis products, and flavonols found in rocket (Eruca sativa and Diplotaxis tenuifolia)

Rocket species have been shown to have very high concentrations of glucosinolates and flavonols, which have numerous positive health benefits with regular consumption. This review highlights how breeders and processors of rocket species can utilize genomic and phytochemical research to improve varieties and enhance the nutritive benefits to consumers. Plant breeders are increasingly looking to new technologies such as HPLC, UPLC, LC-MS, and GC-MS to screen populations for their phytochemical content to inform plant selections. This paper collates the research that has been conducted to date in rocket and summarizes all glucosinolate and flavonol compounds identified in the species. The paper emphasizes the importance of the broad screening of populations for phytochemicals and myrosinase degradation products, as well as unique traits that may be found in underutilized gene bank resources. This review also stresses that collaboration with industrial partners is becoming essential for long-term plant breeding goals through research.

Nitrates and glucosinolates as strong determinants of the nutritional quality in rocket leafy salads

Rocket is an important leafy vegetable crop and a good source of antioxidants and anticancer molecules such as glucosinolates and other sulfur compounds. Rocket is also a hyper-accumulator of nitrates which have been considered for long time the main factors that cause gastro-intestinal cancer. In this review, the content of these compounds in rocket tissues and their levels at harvest and during storage are discussed. Moreover, the effect of these compounds in preventing or inducing human diseases is also highlighted. This review provides an update to all the most recent studies carried out on rocket encouraging the consumption of this leafy vegetable to reduce the risk of contracting cancer and other cardiovascular diseases.

Masking Vegetable Bitterness to Improve Palatability Depends on Vegetable Type and Taste Phenotype

Consumption of dark green vegetables falls short of recommendations, in part, because of unpleasant bitterness. A laboratory-based study of 37 adults was used to determine bitter and hedonic responses to vegetables (asparagus, Brussels sprouts, kale) with bitter masking agents (1.33 M sodium acetate, 10 and 32 mM sodium chloride, and 3.2 mM aspartame) and then characterized by taste phenotype and vegetable liking. In repeated-measures ANOVA, aspartame was most effective at suppressing bitterness and improving hedonic responses for all sampled vegetables. Among the sodium salts, 32 mM sodium chloride decreased bitterness for kale and sodium acetate reduced bitterness across all vegetables with a tendency to increase liking for Brussels sprouts, as release from mixture suppression increased perceived sweetness. Participants were nearly equally divided into three 6-n-propylthiouracil (PROP) phenotype groups. Those tasting the least PROP bitterness (non-tasters) reported least vegetable bitterness, and the additives produced little change in vegetable liking. Aspartame persisted as the most effective bitter blocker for the PROP tasters (medium, supertasters), improving vegetable liking for the medium tasters but too much sweetness for supertasters. The sodium salts showed some bitter blocking for PROP tasters, particularly sodium acetate, without significant gains in vegetable liking. Via a survey, adults characterized as low vegetable likers reported greater increase in vegetable liking with the maskers than did vegetable likers. These results suggest that bitter masking agents (mainly sweeteners) can suppress bitterness to increase acceptance if they are matched to perceived vegetable bitterness or to self-reported vegetable disliking.