Nitrate and nitrite content in organically cultivated vegetables

The nitrate and nitrite content of leaf vegetables (Swiss chard, sea beet, spinach and cabbage), “inflorescence” vegetables (cauliflower) and fruit vegetables (eggplant and vegetable marrow) grown with organic fertilizers have been determined by a modified cadmium–Griess method. Samples were purchased from organic food stores as well as collected directly from an organic farm in Madrid (Spain). Nitrate levels were much higher in the leaf vegetables (especially Swiss chard species; average over the different samples and species of 2778.6 ± 1474.7 mg kg^{? 1}) than in inflorescence or fruit products (mean values between 50.2 ± 52.6 and 183.9 ± 233.6 mg kg^{? 1}). Following Swiss chard species, spinach (1349.8 ± 1045.5 mg kg^{? 1}) showed the highest nitrate content, and nitrite was found above the limit of detection in some samples only (spinach, 4.6 ± 1.0 mg kg^{? 1}; sea beet, 4.2 ± 0.7 mg kg^{? 1} and Swiss chard, 1.2 ± 0.4 mg kg^{? 1}). Some vegetables (spinach, cabbage and eggplant) had lower nitrate content in the samples harvested in summer, showing the influence of climatic conditions on the nitrate levels in a plant. The samples taken directly from the organic farm, with the exception of eggplant, had higher or slightly higher average nitrate values than samples purchased in the organic food stores, ranging from 117 to 1077%.     

Application of lactic acid bacteria starter cultures for decreasing the biogenic amine levels in sauerkraut

Sauerkrauts from shredded white cabbage of six varieties were prepared in six laboratory experiments by initial fermentation at 22 °C for 14 days, then stored at 5-6 °C and analysed after 6 months. Seven biogenic amines were extracted with perchloric acid and determined as N-benzamides by micellar electrokinetic capillary chromatography. Eight common sauerkraut quality parameters were also determined. In three experiments, a commercial strain of Lactobacillus plantarum and a mixed preparation of Microsil containing L. plantarum, Lactobacillus casei, Enterococcus faecium and Pediococcus pentosaceus, were applied at doses of 5᎒⁴, 1᎒⁵ and 5᎒⁵ CFU/g of cabbage. In three further experiments, L. plantarum, Microsil and a commercial strain of Lactobacillus buchneri were applied at doses of 5᎒⁵ and 5᎒⁶ CFU/g. Spontaneously fermented sauerkrauts were prepared as the control variants in all experiments. L. plantarum at doses of at least 5᎒⁵ CFU/g significantly (P<0.05) suppressed formation of putrescine, tyramine and cadaverine, amines occurring at the highest levels. Spermidine contents varied between 10 and 30 mg/kg and were not affected by the starter cultures. Levels of tryptamine, spermine and histamine were very low, often below the detection limits. For practical application, a dose of at least 5᎒⁶ CFU/g of the tested L. plantarum strain seems to be likely. The tested strains of L. buchneri and E. faecium showed tyrosine decarboxylase activity in an in vitro test.     

Nitrate and nitrite levels in commonly consumed vegetables in Hong Kong

Levels of nitrate and nitrite in 73 different vegetables, a total of 708 individual samples grouped into leafy, legumes, root and tuber, and fruiting vegetables, which are traded mainly in Hong Kong, were measured. Where available, five samples of each vegetable type were purchased from different commercial outlets during the winter of 2008 and summer of 2009. Levels of nitrate and nitrite were determined by ion chromatography and flow injection analysis, respectively. Nitrate and nitrite levels of all samples ranged <4–6300 and <0.8–9.0 mg?kg^?1, respectively. Nitrate concentrations for the different groups, in descending order, were leafy?>?root and tuber?>?fruiting and legume vegetables. More than 80% of vegetables had mean nitrate concentrations less than 2000?mg?kg^?1, but mean nitrate concentrations of three types of leafy vegetables, namely Chinese spinach, Shanghai cabbage and Chinese white cabbage, were >3500?mg?kg^?1. On the other hand, nitrite concentrations were generally low –?<1?mg?kg^?1 on average. Nitrate in vegetables (i.e. Chinese flowering cabbage, Chinese spinach and celery) can be reduced significantly (12–31%) after blanching for 1–3?min, but not after soaking.     

Phenols and metals in sugar-cane spirits. Quantitative analysis and effect on radical formation and radical scavenging

A fluorescence-based analytical method for quantification of phenolic compounds in sugar cane spirits (and other distilled alcoholic beverages) was developed. Sample preparation involved reverse-phase solid phase extraction and separation by gradient reversed-phase HPLC with fluorescence detection. Twenty-one Brazilian sugar cane spirits (aged and non-aged cachaça) were analyzed and phenol, guaiacol, o-cresol, p-/m-cresol, 3, 5-xylenol, 4-ethylphenol, 4-ethylguaiacol, 2-ethylphenol, eugenol, (+)-catechin, (-)-epicatechin, and scopoletin quantified. The detection limit was between 0.01 mg l^-1 (eugenol and scopoletin) and 0.1 mg l^-1 [(+)-catechin and (-)-epicatechin]. Kaempferol and quercetin were quantified in the same spirits, together with copper and iron, using HPLC (spectrophotometric detection) and atomic absorption spectroscopy, respectively. Large variations between various spirits were noted: total phenols were between 1.5 and 70 mg l^-1, flavonoids were from below detection to 3.5 mg l^-1, Cu was between 0.04 and 7.0 mg l^-1; and Fe between 0.01 and 0.78 mg l^-1. The tendency of radical formation in the spirits was determined by electron spin resonance spectroscopy using N-t-butyl-!-phenylnitrone spin trapping, and radical scavenging capacity was determined spectrophometrically using the stable 2,2-diphenyl-1-picrylhydrazyl radical as probe. Radical formation depends mainly on the Cu content, while the radical scavenging and antioxidative capacity mainly depends on the flavonoid content. (+)-Catechin and (-)-epicatechin are most important for the antioxidative capacity as confirmed in a model experiment, where oxidation was induced by iron catalysis.     

Linalool disaccharides as flavour precursors from green coffee beans (<Emphasis Type="Italic">Coffea arabica</Emphasis>)

Two linalool disaccharides, isolated from green coffee beans (Coffea arabica), were identified as 3(S)-linalool-3-O-#-D-glucopyranosyl-#-D-apiofuranoside and 3(S)-linalool-3-O-#-D-glucopyranosyl-!-L-arabinopyranoside. The structures were established by one- and two-dimensional ¹H and ¹³C NMR spectra as well as by ESI MS/MS spectra.     

The \delta{}^{18}{\rm O} -value of the p-OH group of L-tyrosine permits the assignment of its origin to plant or animal sources

The biosynthesis of L-tyrosine in plants by the shikimate pathway via arogenate implies that the oxygen atom in the p-position originates from D-erythrose with a d¹⁸O \delta{}^{18}{\rm O} -value near +30‰ above leaf water, while its synthesis in animals by hydroxylation of external L-phenylalanine with O₂ as oxygen source and a kinetic isotope effect k₁₆/k₁₈ɏ.018 demands a d¹⁸O \delta{}^{18}{\rm O} -value near +6‰. These expectations are fully confirmed by experimental data from the ¹⁸O-pattern analysis of natural aromatic compounds. The result is considered as a basis for the assignment of L-tyrosine and L-tyrosine-derived material of plant or animal origin, respectively, and for the determination of the relative amounts of plant and animal material in food and animal feed.     

Identification and quantitation of flavonols in rowanberry (Sorbus aucuparia L.) juice

Eight flavonols were detected in rowanberry juice, six quercetin and two kaempferol glycosides which were identified as quercetin 3-O-galactoside, quercetin 3-O-glucoside, two quercetin 3-O-dihexosides, quercetin pentose-hexoside and quercetin hexose-pentoside and two kaempferol dihexosides. The total content of identified flavonols in the rowanberry juice was 291 mg L^-1. Quercetin dihexosides contributed 78% to the flavonol content. However, chlorogenic and neochlorogenic acid were the most abundant phenolic compounds in the rowanberry juice (544 and 273 mg L^-1, respectively). From a nutritional point of view, rowanberry juice provides 70 mg of flavonols and 196 mg of chlorogenic acids per serving. HPLC-MSⁿ and HPLC-DAD in combination with solid phase extraction were used to obtain these results.     

Differentiation of natural and synthetic phenylacetic acids by 2H NMR of the derived benzoic acids

The origin of 11 samples of phenylacetic acid 4, including those microbially produced from L-phenylalanine 1 and obtained by hydrolysis of penicillin G, has been studied by natural abundance deuterium NMR spectroscopy. The analysis performed on 4 failed since the (D/H) values relative to the aromatic ring nuclei and to the methylene moieties of the analysed phenylacetic acid samples resulted as similar. The permanganate oxidation of 4 into benzoic acid 5 allowed a differentiation in the ²H NMR spectrum of the signals of the ortho, meta and para nuclei of the aromatic ring, which instead for phenylacetic acid collapse in a single signal. Considering the deuterium content of the different positions in the aromatic ring, the differentiation between the natural rather than synthetic origin of the skeleton of the examined products was possible. The deuterium content of the aromatic ring for the synthetic materials is near to the statistical distribution, whereas for the products of natural derivation it follows a para>ortho>meta enrichment.     

Characterisation of novel 1H,4H-quinolizinium-7-olate chromophores by application of colour dilution analysis and high-speed countercurrent chromatography on thermally browned pentose/L-alanine solutions

Thermal treatment of aqueous solutions of xylose and L-alanine at pH 5.0 resulted in the formation of various coloured compounds, which were ranked according to their colour impactsby application of the recently developed colour dilution analysis. High-speed countercurrent chromatography was then successfully used for the first time to isolate colour-intense reaction products from complex Maillard mixtures, amongst which the structures of 2-[(2-furyl)methylidene]-4-hydroxy-5-methyl-2H-furan-3-one (1), and of the novel compounds 3-(2-furyl)-8-[(2-furyl)methyl]-4-hydroxymethyl-1-oxo-1H,4H-quinolizinium-7-olate (2) and 3-(2-furyl)-8-[(2-furyl)methyl]-4,5-bis(hydroxymethyl)-1-oxo-1H,4H-quinolizinium-7-olate (3) were determined by LC/MS, 1D and 2D NMR as well as UV/Vis spectroscopy. To measure the contribution of these colorants to the overall colour of the browned Maillard mixture, colour activity values were calculated as the ratio of the concentration to the visual detection threshold of each colorant. By application of this colour activity concept, 2.2% of the total colour of the thermally browned xylose/L-alanine solution was shown to be covered by the novel 1H,4H-quinolizinium-7-olate chromophores 2 and 3.     

Nitrate in leafy vegetables,culinary herbs,and cucumber grown under cover in Estonia: content and intake

The content of nitrate in leafy vegetables, culinary herbs, and cucumber was determined during the years 2006–2008. All samples of Estonian origin, except white cabbage, were grown under cover. Seasonal differences in nitrate concentrations were observed in lettuce and spinach. Nitrate concentrations in lettuce were 22% and those in spinach were 24% higher in winter crops compared with samples collected in summer. The mean nitrate level was 3023 mg kg^–1 for fresh lettuce and 2337 mg kg^–1 for spinach. On average, 11.6% of fresh lettuce and spinach samples nitrate concentration exceeded the maximum level specified in European Commission Regulation No. 1881/2006. The mean levels were 999 mg kg^–1 for imported iceberg lettuce and 1287 mg kg^–1 for frozen spinach, which are below the maximum European Commission limits. Parsley, dill, basil, thyme, and rucola contained high concentrations of nitrate from mean levels of 2134 mg kg^–1 for parsley up to 8150 mg kg^–1 for rucola. Mean nitrate concentrations ranged from 382 to 1115 mg kg^–1 for white cabbage and Chinese cabbage, respectively. The per capita mean daily intake of nitrates related to the consumption of leafy vegetables, culinary herbs, and cucumber for the whole Estonian population was 31.3 mg day^–1, which comprised 14.2% of the acceptable daily intake (ADI).     

Changes to polyphenols in the process of production of must and wines from blackcurrants and cherries. Part I. Total polyphenols and phenolic acids

The effect of pulp treatment on the qualitative and quantitative changes to polyphenol compounds exhibiting antioxidant properties, in musts and wines from blackcurrants and cherries was investigated. The following variants of pulp treatment were used: hot maceration, hot maceration and pulp pectinolysis with Rohapect MA Plus and Pektopol PM preparations, and also pulp pectinolysis with Rohapect and Pektopol preparations. Blackcurrant musts contained from 4800 to 6600 mg l^-1 of total polyphenols and cherry musts from 3060 to 3920 mg l^-1. The fermentation process caused a decrease in polyphenols content of approximately 25%. In production of fruit wines, the pulp treatment method had a considerable effect on the total content of polyphenols. In blackcurrant wines the highest extraction of polyphenols was obtained after pectinolysis with a Rohapect preparation. In the case of cherry wines the highest content of these compounds was extracted during pectinolysis with a Pektopol preparation. In musts and wines the presence of the following compounds, derivatives of hydroxycinnamic acid, was determined: neochlorogenic, chlorogenic, caffeic, p-coumaric and ferulic acids. The content of neochlorogenic acid was the highest both in musts and wines from blackcurrants and cherries and amounted to 41.7-126.3 mg l^-1, and 24.7-35.3 mg l^-1 respectively for blackcurrants and 74.3-87.7 mg l^-1and 44.5-71.4 mg l^-1 respectively for cherries. The enzymatic preparation Pektopol PM contained an enzyme acting as depsidase. It broke down chlorogenic acid and other compounds to simple phenolic acids (caffeic acid, p-coumaric acid).     

Total phenol,flavonoid, proanthocyanidin and vitamin C levels and antioxidant activities of Mauritian vegetables

Ten Mauritian vegetables, broccoli, cauliflower, white cabbage, lettuce, Chinese cabbage, mugwort, carrot, onion, tomato and chilli pepper, were analysed for their total phenol, flavonoid, proanthocyanidin and vitamin C contents and antioxidant capacity. Antioxidant activities of the vegetables ranged from 0.43 to 3.68 µmol g^?1 fresh weight Trolox equivalent antioxidant capacity (TEAC) and from 0.60 to 8.47 µmol g^?1 fresh weight ferric reducing antioxidant power (FRAP). Levels of total phenols in the vegetables varied between 132 and 1189 µg g^?1 fresh weight and those of total flavonoids between 45 and 944 µg g^?1 fresh weight, while proanthocyanidins were detected at very low levels in only a few vegetables. Vitamin C contents varied between 25 and 748 µg g^?1 fresh weight. Quercetin was the dominant flavonoid aglycone in the hydrolysed vegetable extracts, with values in the range of 15–390 µg g^?1 fresh weight. There were strong correlations between antioxidant capacity and total phenols (TEAC, r = 0.91; FRAP, r = 0.83) and total flavonoids (TEAC, r = 0.89; FRAP, r = 0.82). Vitamin C contents showed poor correlation with TEAC values (r = 0.33), while no correlation was observed with FRAP values. Highest antioxidant capacities were observed in Chinese cabbage (Brassica chinensis L), onion (Allium cepa L), mugwort (Artemisia vulgaris Cantley) and broccoli (Brassica oleracea L var botrytis L subvar cymosa). Mauritian vegetables therefore represent a significant source of phenolic antioxidants, with quercetin derivatives being most abundant, and this may contribute to their potential health benefits. Copyright © 2004 Society of Chemical Industry     

Nitrate-N determination in leafy vegetables: Study of the effects of cooking and freezing

Nitrate upon reduction to nitrite can cause methaemoglobinaemia or act as precursor in the endogenous formation of carcinogenic nitrosamines. The leafy vegetables are the major vehicle for the entry of nitrate into the human system. The present study was conducted to establish a flow injection analysis (FIA) technique to investigate the nitrate-N contents of four commonly consumed fresh leafy vegetables (Chinese cabbage, celery, lettuce and English cabbage) from market in Fiji. Two extraction techniques (activated carbon and alkaline extraction) were assessed to extract nitrate-N and the activated carbon extraction was preferred over alkaline extraction and applied. The recoveries of spiked nitrate-N in vegetable matrices ranged from 90.40% to 112.80% in activated carbon extraction with an average of 100.62%. The effects of cooking (boiling, baking and frying) and deep-freezing on the nitrate-N contents were also studied. Nitrate contents in selected leafy vegetables were determined by FIA coupled with Greiss protocol involving sulfanilamide and N-(1-naphthyl)ethylenediamine dihydrochloride as color reagents. Nitrate was determined in the linear range from 1.0 to 20.0 mg L⁻¹ with the method detection limit of 0.042 mg L⁻¹ (0.34 mg kg⁻¹). The results of the study show that nitrate contents in fresh leafy vegetables ranged from 1297 to 5658 mg kg⁻¹. Boiling reduces nitrate content by 47–56% whereas frying in Soya bean oil elevates nitrate content by as much as 159–307%. No significant change was observed in nitrate content after baking. The deep-freezing of the selected leafy vegetables shows that nitrate-N content fluctuates slightly from the original nitrate-N values over the seven day period. The FIA throughput was 38 samples h⁻¹.     

α-Amylases in raw and fermented African oil bean seeds (Pentaclethra macrophylla benth)

The !-amylases of raw and fermented seeds of African oil bean (Pentaclethra macrophylla Benth) were isolated, partially purified (tenfold) and subjected to different thermal and pH conditions. The specific activities of the purified enzyme from raw and fermented seeds were 0.037 ml^-1 min^-1 and 0.88 ml^-1 min^-1 respectively. The !-amylase from fermented seeds was more thermostable with optimum activity at 70 °C, compared to the optimum temperature of 60 °C obtained for the raw seed enzyme. The assayed !-amylases were stable over a wide range of pH (3.0-7.0), with optimum activity found at pH 6.0 and pH 5.0 for raw and fermented seeds respectively. The results show that the !-amylase of Pentaclethra macrophylla complements the microbial amylases in the mainly bacterial fermentation of African oil bean seeds to 'ugba', a highly nutritious food condiment. While the !-amylase in the raw seeds was basically the plant enzyme, that isolated from the fermented seeds was a combination of plant and microbial !-amylases.     

The effect of cooking on the glucosinolates content in white cabbage

The effect of different cooking times on the GLS content in white cabbage (Brassica oleracea L. var. capitata f. alba) was determined. Cooking of cabbage for 5-30 min caused a gradual decrease in the GLS content. The most efficient reduction of the GLS content (by about 35%) occurred during the first minutes of cooking. As the cooking time was extended by another 5 min, each time the GLS content decreased by 10-15%. Higher losses in indole GLS, as compared to those of aliphatic ones, resulted from more efficient diffusion of those compounds to cooking water. The GLS content in cooking water, irrespective of the cooking time of white cabbage, remained rather stable, whereas the content of indole GLS was between 3.5- and 4-fold higher in comparison to that of aliphatic GLS. Taking into consideration the rate of changes in the content of particular GLS in cabbage and the GLS content in cooking water, it can be stated that glucoiberin was more thermolabile than other GLS.     

Controlling (bio)chemical conversions of health-related plant-based compounds by processing: The case of Brussels sprouts and leek

Brussels sprouts and leek are suppliers of multiple health-related compounds, yet understudied on how processing impacts their concentration. In this study, the plant tissue structure was altered by processing to direct endogenous enzyme-substrate interactions. For this, both conventional and novel processing techniques were employed. Heating intact vegetables prior to high shear mixing resulted in relatively good preservation of health-related compounds, attributed to a prompt inactivation of endogenous enzymes. Oppositely, high shear mixing prior to heating facilitated over 82% conversion for both vitamin C, S-alk(en)yl-L-cysteine sulfoxides (ACSOs) and glucosinolates. Pulsed electric field (PEF) treatment prior to heating, resulted in ±25% ACSOs conversion, yet no glucosinolates conversion. PEF treatment effectiveness is attributed to substrate-enzyme localization in the matrix and cell size. Vitamin K1 remained relatively stable during all treatments. It was postulated that higher concentrations of vitamin C protect carotenoids against oxidation pointing to interaction effects among health-related compounds.Industrial relevance textThis research paper gives more insight into how (the sequence of) commonly used pretreatments (e.g. heating, mixing) and more innovative pretreatments (e.g. pulsed electric field) can have an impact on the health potential of vegetables. The considered vegetables (Brussels sprouts and leek) are highly industrial relevant and insights may be extrapolated to other vegetables of these large plant families. By understanding which (bio)chemical reactions can occur during certain pretreatments (e.g. degradation or potential formation of health-related compounds), industry can perform pretreatments more thoughtfully and consequently steer the health potential of vegetable products. Pulsed electric fields are currently not commonly used in vegetable processing. However, this processing technique can enable certain enzymatic conversions, of which some could result in formation of health beneficial compounds, without losing the vegetable structure. Therefore, applying pulsed electric fields in the vegetable processing industry could have large potential. The aim of this research is to open the door to more research on pulsed electric fields applied on vegetables, so the vegetable industry becomes acquainted with using this technique.     

A comparative study on the polyphenolic content,antibacterial activity and antioxidant capacity of different solvent extracts of Brassica oleracea vegetables

Brassica vegetables are rich in polyphenols, flavonoids and glucosinolates. Investigation was undertaken to optimise the best solvents among 60% ethanol, acetone and methanol for the extraction of polyphenols from Brassica vegetables. Furthermore, different properties such as antibacterial activity and antioxidant capacity were also investigated. Results showed that a 60% methanolic extract showed the highest total phenolic content which was 23.6, 20.4 and 18.7 mg gallic acid equivalents (GAE) g^?1 extract for broccoli, Brussels sprouts and white cabbage, respectively. The hydroxybenzoic acid content of various solvent extracts ranged from 5.86 to 8.91 GAE g^?1 extract for broccoli, 2.70 to 5.44 GAE g^?1 extract for Brussels sprouts and 3.69 to 4.86 GAE g^?1 extract for white cabbage, while the hydroxycinnamic acid content ranged from 0.78 to 1.26 chlorogenic acid equivalents (CAE) g^?1 extract for broccoli, 1.41 to 3.45 CAE g^?1 extract for Brussels sprouts and 0.49 to 1.14 CAE g^?1 extract for white cabbage. A concentration‐dependent antioxidative capacity was confirmed for different reactive oxygen species, and moderate antibacterial activity was observed against a number of Gram‐negative and Gram‐positive food spoilage and food pathogenic bacteria. Solvents significantly affected polyphenolic content and its different properties, and the methanol was found to be the best solvent for the extraction of polyphenols from studied Brassica vegetables.     

In vivo or in vitro application of vitamin E and the colour stability of low-oxygen packaged,sliced, pasteurised,differently cured pork shoulder model products

The effect of dietary supplementation with vitamin E vs the in vitro addition of vitamin E on the colour stability of pasteurised comminuted pork shoulder model products was studied. Products were either manufactured with normal amounts of nitrite and ascorbate or with reduced levels of the additives. Half of the samples of sliced products from control meat (CON), from control meat supplemented in vitro with 5 and 50 mg kg^-1 vitamin E and from meat derived from pigs receiving vitamin E supplements (SUP) were packaged under vacuum (VAC) and half in low-oxygen modified atmosphere packs (FOG). Duplicate packages were stored in the dark and under constant illumination for 21 days at 7 °C. For the illuminated VAC-packaged products, significant temporary decreases in the redness values were observed for CON and the in vitro addition of 5 mg kg^-1 vitamin E to CON. Both dietary supplementation with approximately 5 mg kg^-1 extra vitamin E and the in vitro addition of 50 mg kg^-1 vitamin E to CON were effective in preventing the temporary decrease in redness values. At the end of the experiment, the redness values of the VAC products approximated initially measured levels. The colour of the illuminated FOG-packaged products was stable throughout storage and the redness values of the SUP products were significantly better than those of the CON products. The in vitro addition of vitamin E had no effect on redness values here. The colour stability of VAC-packaged products containing the combination of reduced levels of nitrite and ascorbate was diminished in the initial period of illuminated storage. Similar effects were not observed for FOG-packaged products.     

Glucosinolate content of Brassica vegetables-Chinese cabbages Pe-tsai (Brassica pekinensis) and Pak-choi (Brassica chinensis)

The glucosinolate content of 19 cultivars of pe-tsai and three cultivars of pak-choi Chinese cabbage (Brassica pekinensis Lour) Rupr and (Brassica chinensis L, respectively) has been determined using high performance liquid chromatography. The levels of total glucosinolates were 0.097-0.337 g kg^?1 fresh weight (mean 0.198) in pe-tsai and 0.39-0.704 g kg^?1 (mean 0.534) in pak-choi. The main components present were (2-hydroxybut-3-enyl-progoitrin), but-3-enyl- (gluconapin), 5-methylsulphinylpentyl- (glucoalyssin) and pent-4-enyl (glucobrassicanapin) glucosinolates, respectively. In comparison with other UK brassicas and American cultivars of Chinese cabbage, both the UK-grown pak-choi and pe-tsai are low in glucosinolates.     

Soil and vegetable compositional relationships of eight potentially toxic metals in urban garden fields from northern Nigeria

BACKGROUND: Human exposure to heavy metals is attributed to consumption of vegetables raised in polluted soil environment. We examined the concentrations of As, Cd, Co, Cr, Cu, Ni, Pb and Zn in soils and lettuce (Latuca sativa) and amaranthus (Amaranthus caudatus) in 15 garden fields under long‐term wastewater irrigation. RESULTS: The concentrations of As (0.3–2.1 mg kg^?1), Cd (0.07–0.3 mg kg^?1), Co (4.6–9.1 mg kg^?1) and Cr (21.6–36.2 mg kg^?1) in the gardens were consistent with background concentrations in soils, but Ni (12.6–25.7 mg kg^?1), Cu (12.5–24.6 mg kg^?1), Pb (25.7–71.6 mg kg^?1) and Zn (52.3–158 mg kg^?1) concentrations were double the concentrations normally encountered in arable fields in the region. The concentrations of Cd and As in the vegetables were within safe limits, but Co (0.14–0.67 mg kg^?1 fresh weight (fw)) and Ni (1.0–2.7 mg kg^?1 fw) concentrations in lettuce were relatively high for leaf vegetables. The concentration of Pb (0.65–4.80 mg kg^?1 fw) was above safe limit of 0.3 mg kg^?1 fw, while the concentrations of Cu (1.3–2.7 mg kg^?1 fw and Zn (10.2–23.6 mg kg^?1 fw) were close to the unsafe limits for leaf vegetables. There were no strong linear correlations between soil metal concentrations and bio‐concentrations in the vegetable crops. CONCLUSION: We surmise that leaf vegetables can accumulate metals in their tissues to unsafe levels even when total metal concentrations in these soils are below the allowable concentrations in agricultural soils. Copyright © 2008 Society of Chemical Industry