Marta Francisco

Phenolic Compounds in Brassica Vegetables

Phenolic compounds are a large group of phytochemicals widespread in the plant kingdom. Depending on their structure they can be classified into simple phenols, phenolic acids, hydroxycinnamic acid derivatives and flavonoids. Phenolic compounds have received considerable attention for being potentially protective factors against cancer and heart diseases, in part because of their potent antioxidative properties and their ubiquity in a wide range of commonly consumed foods of plant origin. The Brassicaceae family includes a wide range of horticultural crops, some of them with economic significance and extensively used in the diet throughout the world. The phenolic composition of Brassica vegetables has been recently investigated and, nowadays, the profile of different Brassica species is well established. Here, we review the significance of phenolic compounds as a source of beneficial compounds for human health and the influence of environmental conditions and processing mechanisms on the phenolic composition of Brassica vegetables.

Simultaneous identification of glucosinolates and phenolic compounds in a representative collection of vegetable Brassica rapa.

Brassica raparapa group is widely distributed and consumed in northwestern Spain. The consumption of Brassica vegetables has been related to human health due to their phytochemicals, such as glucosinolates and phenolic compounds that induce a variety of physiological functions including antioxidant activity, enzymes regulation and apoptosis control and the cell cycle. For first time in Brassica crops, intact glucosinolates and phenolic compounds were simultaneously identified and characterized. Twelve intact glucosinolates, belonging to the three chemical classes, and more than 30 phenolic compounds were found in B. rapa leaves and young shoots (turnip greens and turnip tops) by LC-UV photodiode array detection (PAD)-electrospray ionization (ESI). The main naturally occurring phenolic compounds identified were flavonoids and derivatives of hydroxycinnamic acids. The majority of the flavonoids were kaempferol, quercetin and isorhamnetin glycosylated and acylated with different hydroxycinnamic acids. Quantification of the main compounds by HPLC-PAD showed significant differences for most of compounds between plant organs. Total glucosinolate content value was 26.84 micromol g(-1) dw for turnip greens and 29.11 micromol g(-1) dw for turnip tops; gluconapin being the predominant glucosinolate (23.2 micromol g(-1) dw). Phenolic compounds were higher in turnip greens 51.71 micromol g(-1) dw than in turnip tops 38.99 micromol g(-1) dw, in which flavonols were always the major compounds.

Phytochemical fingerprinting of vegetable Brassica oleracea and Brassica napus by simultaneous identification of glucosinolates and phenolics

INTRODUCTION Brassica vegetables have been related to the prevention of cancer and degenerative diseases, owing to their glucosinolate and phenolic content. OBJECTIVE Identification of glucosinolates, flavonoids and hydroxycinnamic acids in representative varieties of kale, cabbage and leaf rape. METHODOLOGY One local variety of each crop was evaluated in this study using a multi-purpose chromatographic method that simultaneously separates glucosinolates and phenolics. Chromatograms were recorded at 330 nm for flavonoid glycosides and acylated derivatives and 227 nm for glucosinolates. RESULTS Eight glucosinolates were identified in kale and cabbage, which exhibited the same glucosinolate profile, and 11 glucosinolates were identified in leaf rape. Furthermore, 20 flavonoids and 10 hydroxycinnamic acids were detected in kale and cabbage, while 17 flavonoids and eight hydroxycinnamic acids were found in leaf rape. CONCLUSIONS This study has provided a deeper and comprehensive identification of health-promoting compounds in kale, cabbage and leaf rape, thus showing that they are a good source of glucosinolates and phenolic antioxidants.

New insights into antioxidant activity of Brassica crops

Antioxidant activity of six Brassica crops-broccoli, cabbage, cauliflower, kale, nabicol and tronchuda cabbage-was measured at four plant stages with DPPH and FRAP assays. Samples taken three months after sowing showed the highest antioxidant activity. Kale crop possessed the highest antioxidant activity at this plant stage and also at the adult plant stage, while cauliflower showed the highest antioxidant activity in sprouts and in leaves taken two months after sowing. Brassica by-products could be used as sources of products with high content of antioxidants. Phenolic content and composition varied, depending on the crop under study and on the plant stage; sprout samples were much higher in hydroxycinnamic acids than the rest of samples. Differences in antioxidant activity of Brassica crops were related to differences in total phenolic content but also to differences in phenolic composition for most samples.

Antiproliferative Activity of the Dietary Isothiocyanate Erucin, a Bioactive Compound from Cruciferous Vegetables, on Human Prostate Cancer Cells

It is becoming increasingly clear that many dietary agents, such as isothiocyanates (ITCs) from cruciferous vegetables, can retard or prevent the process of prostate carcinogenesis. Erucin (ER) is a dietary ITC, which has been recently considered a promising cancer chemopreventive phytochemical. The potential protective activity of ER against prostate cancer was investigated using prostate adenocarcinoma cells (PC3), to analyze its effects on pathways involved in cell growth regulation, such as the cyclin-dependent kinase (CDKs) inhibitor p21WAF1/CIP1 (p21), phosphatidylinositol-3 kinase/AKT, and extracellular signal-regulated kinases (ERK)1/2 signaling pathways. We have shown for the first time that ER increases significantly p21 protein expression and ERK1/2 phosphorylation in a dose-dependent manner to inhibit PC3 cell proliferation (P ≤ 0.01). Compared to the structurally related sulforaphane, a well-studied broccoli-derived ITC, ER showed lower potency in inhibiting proliferation of PC3 cells, as well as in modulating p21 and pERK1/2 protein levels. Neither of the naturally occurring ITCs was able to affect significantly pAKT protein levels in prostate cells at all concentrations tested (0–25 μM). It is clearly important for the translation of laboratory findings to clinical approaches to investigate in animal and cell studies the molecular mechanisms by which ITCs may exert health promoting effects.

Effect of genotype and environmental conditions on health-promoting compounds in Brassica rapa.

It is well-known that a variety of factors (genetic and environmental) affect the ultimate metabolite levels in brassica vegetables, although there is still little information about the role that genetics and environment play on glucosinolates and phenolic levels. Total glucosinolates were more abundant in turnip tops (26.02 μmol g(-1) dw) than in turnip greens (17.78 μmol g(-1) dw). On the other hand, total phenolic content was found in higher quantities in turnip greens (43.81 μmol g(-1) dw) than in turnip tops (37.53 μmol g(-1) dw). Aliphatic glucosinolates were clearly regulated by genotype; in contrast, the effects of environment and genotype×environment interaction on the indolic glucosinolate and phenolic compounds content appeared to be the main effects of variation. Identification of genotypes with enhanced and stable levels of these compounds would provide a value-added opportunity for marketing this crop with superior health promotion to consumers.

Resistance of Cabbage (Brassica oleracea capitata Group) Crops to Mamestra brassicae

ABSTRACT Twenty-one cabbage (Brassica oleracea capitata group) varieties, including 16 local varieties and five commercial hybrids, were screened for resistance to the moth Mamestra brassicae L. under natural and artificial conditions in northwestern Spain. Resistance was assessed as the proportion of damaged plants and damaged leaves, leaf feeding injury, and number of larvae present. Correlation coefficients among damage traits showed that a visual scale (general appearance rating) should be a useful indicator of resistance. Most local varieties were highly susceptible to M. brassicae, whereas the commercial hybrids tested were resistant in terms of head foliage consumption and number of larvae per plant. Performance of varieties was similar under natural and artificial infestation although some of them performed differently at each year. Three local varieties (MBG-BRS0057, MBG-BRS0074, and MBG-BRS0452) were highly susceptible at both natural and artificial infestation conditions being MBG-BRS0074 the most damaged variety. Two local varieties (MBG-BRS0402 and MBG-BRS0535) and commercial hybrids were identified as resistant or moderately resistant to M. brassicae. Among them, ‘Corazon de Buey’ and ‘Cabeza negra’ were the most resistant and produced compact heads. These varieties could be useful sources of resistance to obtain resistant varieties to M. brassicae or as donors of resistance to other Brassica crops. The possible role of leaf traits, head compactness, and leaf glucosinolate content in relation to M. brassicae resistance is discussed.

In Vivo and in Vitro Effects of Secondary Metabolites against Xanthomonas campestris pv. campestris

Brassica rapa is a crucifer that is grown worldwide, mainly as a vegetable. The quality of B. rapa crops is highly affected by the disease caused by the bacteria Xanthomonas campestris pv. campestris (Xcc). Glucosinolates and phenolic compounds can confer resistance to Brassica crops against pests and diseases, but few works have been done to evaluate their role in Xcc resistance. The objectives of this work were: (1) to evaluate the in vivo and in vitro antibacterial effect of gluconapin, its isothiocyanate and the methanolic extracts of B. rapa against the type 4 of Xcc, and (2) to test if there is induced resistance mediated by glucosinolates or phenolic compounds in two varieties of B. rapa. Gluconapin and its ITC varieties had an antibacterial effect on the development of Xanthomonas and this effect was strongly dependent on the concentration applied. Methanolic extracts from B. rapa, containing glucosinolates and phenolic compounds, inhibited the growth of these bacteria. Concentration of gluconapin is higher in resistant plants than in the susceptible ones and there is an induction of gluconapin, some flavonoids and sinapic acid 48 to 72 h after inoculation. Gluconapin plays a role in the constitutive resistance to Xcc, while gluconapin, some flavonoids and hydroxycinnamic acids are induced by a Xcc infection but it is not clear if this induction confers resistance to this disease.

Environmental and Genetic Effects on Yield and Secondary Metabolite Production in Brassica rapa Crops

Twelve Brassica rapa varieties grown, such as turnip green and turnip top, were evaluated in seven environments to determine the environmental and genotypic variables that have an influence on crop production and on the content of glucosinolates and phenolic compounds. Factorial regression analysis showed that, in general, crop production was favored by high temperatures all along the crop cycle. However, the lack of a period of intense cold could be a limiting factor. The metabolite content seems to be regulated by extreme temperatures (daily maximum and minimum temperatures) rather than by average daily temperatures. With regard to genotypic covariables, turnip top production was significantly affected by traits related to the vegetative development and time to flowering. Meanwhile, turnip green production was largely affected by a sinapoyl derivative compound, which is a precursor of cell wall components. Cross-talk between glucosinolate biosynthesis and phenylpropanoid signaling pathways is suggested.

Genetic structure and diversity of a collection of Brassica rapa subsp. rapa L. revealed by simple sequence repeat markers

This research was supported by project RF-2006-00028-00-00 and the Excma. Diputacion Provincial de Pontevedra, Spain.