Phenolic acids and flavonoids in leaf and floral stem ...

Food Chemistry 126 (2011) 417–422

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Phenolic acids and flavonoids in leaf and floral stem of cultivated and wild Cynara cardunculus L. genotypes Gaetano Pandino a,b, Sara Lombardo a, Giovanni Mauromicale a, Gary Williamson b,⇑ a Dipartimento di Scienze Agronomiche, Agrochimiche e delle Produzioni Animali, Sezione Scienze Agronomiche, Università degli Studi di Catania, via Valdisavoia 5, 95123 Catania, Italy b School of Food Science and Nutrition, University of Leeds, Leeds LS2 9JT, UK

a r t i c l e

i n f o

Article history: Received 30 May 2010 Received in revised form 16 September 2010 Accepted 1 November 2010

Keywords: Cynara cardunculus Caffeoylquinic acids Flavonoids FRAP HPLC–DAD–MS/MS

a b s t r a c t Ten genotypes, cultivated and wild of Cynara cardunculus L. were evaluated for their content of phenolic acids, flavonoids and their antioxidant activity. The major compounds present in the leaf were luteolin derivatives in globe artichoke and apigenin derivatives in wild and cultivated cardoon. Apart from ‘Cimiciusa di Mazzarino’ (var. scolymus), caffeoylquinic acids represent the main phenolic compounds in the floral stem. In particular, ‘Sylvestris Creta’ (var. sylvestris) and ‘Violetto di Sicilia’ (var. scolymus) show the highest content of caffeoylquinic acid 95% of the total measured polyphenols. The antioxidant capacity, in both leaf and floral stem, was qualitatively and quantitatively dependent on the phenolic acid and flavonoid profile. The phenolic acids and flavonoids in normally uneaten parts of wild and cultivated artichoke could be exploited as sources of natural antioxidants. Ó 2010 Elsevier Ltd. All rights reserved.

1. Introduction Polyphenols play an important role in growth, reproduction and protection against abiotic and biotic stressors (Beckman, 2000) and exhibit a wide range of physiological effects when consumed by humans (Manach, Scalbert, Morand, Rémésh, & Jimènez, 2005). In foodstuffs, oxidation causes changes in flavour, texture, colour, and other sensory attributes as well as modifying the nutritional value of food products (Shahidi, 1997). Thus, in the food industry, synthetic antioxidants, such as butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT), have been widely used for extending shelf life (Choi, Song, Ukeda, & Sawamura, 2000). Currently, the perceived safety problems with synthetic antioxidants led to an increased interest for the recovery and exploitation of natural antioxidants (Peschel et al., 2006). In particular, several researchers have investigated the possibility of extracting natural antioxidants from agricultural and industrial residues, such as potato peel waste (Rodriguez de Sotillo, Hadley, & Holm, 1994), olive oil waste waters (Visioli et al., 1999), grape seeds (Yamaguchi, Yoshimura, Nakazawa, & Ariga, 1999), mango peels (Berardini, Knödler, Schieber, & Carle, 2005) and apple pomace (Carle et al., 2001). Cynara cardunculus L. belongs to the Asteraceae (ex Compositae) family, and includes three botanical varieties: globe artichoke [var. scolymus (L.) Fiori], cultivated cardoon (var. altilis DC.) and the ancestor wild cardoon or wild artichoke [var. sylvestris (Lamk) ⇑ Corresponding author. Tel.: +44 113 3438380; fax: +44 113 3432982. E-mail address: [email protected] (G. Williamson). 0308-8146/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodchem.2010.11.001

Fiori]. Their immature inflorescences are consumed fresh, canned or frozen. The cultivation of cardoons is not very widespread, remaining of regional importance in Spain, Italy, Greece and the south of France, where they are consumed in traditional dishes, using the large central ribes and small part of the leaf blade. The wild cardoon is a thistle-like plant spread over the west central part of Mediterranean Basin (continental zone and isles), and the species is also naturalised in North and South America and in Australia. Flowers are used as a rennet substitute in the processing of some regional cheeses in Spain, Portugal and Italy. The globe artichoke is an attractive source of natural antioxidants, since it is rich in polyphenols, mainly phenolic acids and flavonoids (Schütz, Kammerer, Carle, & Schieber, 2004). Although the globe artichoke has the highest total polyphenol content (Brat et al., 2006) and produces a huge amount of agricultural and industrial waste (80–85% of the total plant and 60% of the whole head, respectively) (Llorach, Espin, Tomas-Barberan, & Ferreres, 2002), its use as a source of natural compounds has been little investigated (Lattanzio et al., 2002; Llorach et al., 2002; Peschel et al., 2006). The waste matter is mostly leaves and floral stems. The leaves, rich in flavones, have been widely studied (Wang et al., 2003), while available data on the floral stem, rich in caffeoylquinic acids, are scanty (Romani, Pinelli, Cantini, Cimato, & Heimler, 2006). Their leaves have a high polyphenol content (Pinelli et al., 2007), whereas floral stems have never been studied. The objectives, therefore, of the present study were to investigate the phenolic profile in leaf and floral stem of several genotypes of C. cardunculus; to assess in vitro antioxidant activity of

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these parts of the plant; and to explore the relationship between phenolic compounds and antioxidant capacity. 2. Materials and methods 2.1. Plant material, management pratices and sampling The following were analysed: Six genotypes of globe artichoke – ‘Blanc Hyèrois’, ‘Nobre’, ‘Tempo F1’, ‘Tondo di Paestum’, ‘Tema 2000’ and ‘Violetto di Sicilia’; two accessions of wild cardoon, ‘Sylvestris Creta’ and ‘Sylvestris Kamarina’, native of Crete (Greece) and of Sicily (Italy), respectively; one selection of cultivated cardoon, namely ‘Altilis’, selected by Catania University; and a globe artichoke Sicilian landrace, ‘Cimiciusa di Mazzarino’. All were field-grown in Sicily at the experimental station of Catania University, on the Catania Plain, a typical area for globe artichoke cultivation in Italy, and where the wild cardoon grows naturally. Each one was planted in the form of either semi-dormant offshoots (‘ovoli’) or seeds (achenes) in August 2007. The plant material was arranged in a randomized block experimental design with four replicates. Each field plot consisted of 10 plants, spaced 0.80 m apart with a row spacing of 1.25 m. Crop management (fertilisation, irrigation, weed and pest control) was performed according to the standard commercial practice. At least five leaves and floral stems per replicate were collected when the length of central flower buds of the capitula was about 1.5–2.0 mm (marketing stage to harvest the global artichoke) and washed with tap water. They were then cut and blended using a domestic food processor at 0 °C. Finally, each sample was freeze-dried and stored at 20 °C until analysis. 2.2. Reagents and solvents Reagents and solvents were purchased from VWR (Leighton Buzzard, UK) and were of analytical or HPLC grade. Apigenin7-O-glucoside, apigenin, luteolin-7-O-glucoside, luteolin, 5-Ocaffeoylquinic acid (chlorogenic acid) and hesperetin were obtained from Extrasynthese (Lyon, France), cynarin (1,3-di-O-caffeoylquinic acid) was from Roth (Karlsruhe, Germany). Ferrous sulphate, ferric chloride hexahydrate, sodium acetate trihydrate, butylated hydroxytoluene (BHT) and 2,4,6-Tris(2-pyridyl)-s-triazine (TPTZ) were purchased from Sigma Chemicals Co. (St. Louis, MO). Milli-Q system (Millipore Corp., Bedford, MA) ultrapure water was used throughout this research. 2.3. Extraction procedure The dried samples (100 mg) were extracted in 1 ml of 70% methanol, containing 1 mM butylated hydroxytoluene, to preserve compounds during extraction, and hesperetin, as internal standard, for 1 h at room temperature, with shaking. After centrifugation, the supernatant was transferred to a microfuge tube and the sample was centrifuged once more with 0.25 ml of 70% methanol. The supernatants were combined and kept at 20 °C until analysis (Schütz et al., 2004; Wang et al., 2003).

The method was adapted from Määttä, Kamal-Eldin, and Törrönen (2003): the mobile phase was 1% formic acid in water (solvent A) and in acetonitrile (solvent B) at a flow rate of 0.5 ml/ min. The gradient started with 5% B to reach 10% B at 5 min, 40% B at 20 min, 90% B at 25 min, 90% B at 29 min. Chromatograms were recorded at 280, 310 and 350 nm from diode array data collected between 200 and 600 nm. Identification of single compounds was by their retention times and both UV and MS spectra. Quantification was performed using a calibration curve of the available standards. In particular, mono and dicaffeoylquinic acids were calculated using chlorogenic acid and cynarin as references, respectively. Monosuccinyl-dicaffeoylquinic acids were calculated using cynarin as reference. Apigenin and luteolin conjugates were quantified as apigenin-7-O-glucoside and luteolin-7-O-glucoside, respectively. All data presented are mean values ± standard deviation of three independent experiments and expressed as g kg 1 of dry matter (DM). 2.5. HPLC–MS/MS analysis Analyses were performed using the HPLC system described above, coupled in-line with an Agilent 6410 Triple Quadrupole Mass Spectrometer equipped with Mass Hunter software (version: B.01.04) (Agilent Technologies, Palo Alto, USA). HPLC effluent was diverted to waste for the first 2 min of each chromatographic run, after which negative electrospray (ESI( )) was used to ionise compounds eluting from the column. Nitrogen was used both as drying gas at a flow rate of 6 l/min and as nebulising gas at a pressure of 55 psi. The drying gas temperature was 300 °C, and a potential of 4000 V was applied across the capillary. The fragmentor voltage was 120 V, and the collision voltage was 20 V. Quadrupole 1 filtered the calculated m/z of each compound of interest, whilst quadrupole 2 scanned for ions produced by nitrogen collision of these ionised compounds in the range 100–1000 m/z at a scan time of 500 ms/cycle. 2.6. Determination of antioxidant capacity Antioxidant capacity of sample extracts was determined by FRAP (ferric reducing-antioxidant power) assay, proposed by Benzie and Strain (1996) and then modified by Firuzi, Lacanna, Petrucci, Marrosu, and Saso (2005). The method is based on the reduction of the Fe3+–TPTZ complex to ferrous form at low pH in the presence of antioxidants. Briefly, an aliquot of sample extracts (10 ll) was added to 30 ll of water and 300 ll freshly prepared of FRAP reagent. After 4 and 60 min, this reduction was measured at 595 nm using a microplate reader (Labsystems Multiskan Ascent). Known concentrations of ferrous sulphate, in the range 100– 1750 lmol/l, were used for calibration. These were dissolved in the same solvent used for the extraction, to avoid the effect different solvents might have on the analysis. Results are expressed as mmol Fe2+ kg 1 of dry matter (DM). 3. Results and discussion

2.4. HPLC analysis

3.1. HPLC and HPLC–MS/MS analysis

Each extract (20 ll) was analysed using a series 1200 HPLC (Agilent Technologies, Palo Alto, USA) equipped with ChemStation software (version: B.03.01), a model G1379B degasser, a model G1312B binary gradient pump, a model G1367C thermoautosampler, a model G1316B column oven, and a model G1315C diode array detection system. Separations were achieved on a Zorbax Eclipse XDB-C18 (4.6 50 mm; 1.8 lm particle size), operated at 30C, with a 0.2 lm stainless steel in-line filter.

The main chemical structures of the identified compounds are shown in Fig. 1. The qualitative and quantitative profile of identified compounds, flavones and caffeoylquinic acids, varied between the leaf and the floral stem of all genotypes of C. cardunculus analysed. In the leaf, flavones were the major compounds, whereas in the floral stem, caffeoylquinic acids were the most abundant (Tables 1 and 2). These results show that specific phenolic compounds accumulate in specific parts of the plant and are in agreement with

419


phenylalanine PAL

cinnamic acid

lignans OH

C4H

p-coumaric acid

caffeoylquinic acids: caffeoylquinic acids

O O C HOOC OH OH OH

OH

CHS dicaffeoylquinic acids

p-coumaryl-CoA

OH

OH OH

CHI HOOC

naringenin chalcone

C O O

HO

OH

O C O

4CL HO

naringenin

R

flavones

OH HO

O

Apigenin R= H Luteolin R= OH

H H

OH O

Fig. 1. The general phenylpropanoid pathway and the structures of the major classes of phenolic compounds in C. cardunculus. Abbreviations: PAL, phenylalanine ammonia lyase; C4H, cinnamate 4-hydroxylase; 4CL, 4-coumaroyl-CoA ligase; CHS, chalcone synthase; CHI, chalcone isomerase.

Table 1 Phenolic content (g kg

1

of DM) of C. cardunculus leaves in relation to genotype.

Compound

1-Caffeoylquinic acid 3-Caffeoylquinic acid 5-Caffeoylquinic acid 3,5-Dicaffeoylquinic acid 1,5-Dicaffeoylquinic acid Monosuccinyldicaffeoylquinic acid Monosuccinyldicaffeoylquinic acid Total caffeoylquinic acid Luteolin rutinoside Luteolin glucoside Luteolin glucuronide Luteolin malonylglucoside Luteolin Total luteolin Apigenin rutinoside Apigenin glucoside Apigenin glucuronide Apigenin malonylglucoside Apigenin Total apigenin Total measured polyphenols

Genotype Altilis

Blanc Hyèrois

Nobre

Sylvestris Creta

Sylvestris Kamaryna

Tempo F1

Tondo di Paestum

Tema 2000

Violetto di Sicilia

nd Trace 0.3 nd nd Trace

nd nd 0.9 nd 0.08 nd

nd nd 0.8 nd 0.09 nd

nd nd 0.2 nd nd nd

nd nd nd nd Trace nd

nd nd nd nd nd nd

Trace nd 0.7 nd nd nd

Trace Trace 1.4 ± 0.2 nd 0.1 Trace

nd Trace 2.3 ± 0.2 nd 0.1 nd

nd

Trace

nd

nd

nd

nd

Trace

Trace

Trace

0.3 nd 0.1 2.4 ± 0.3 nd 0.9 ± 0.1 3.4 0.5 0.1 3.3 ± 0.3 0.4 1.3 ± 0.2 5.6 9.3

1.0 3.1 2.4 nd 1.6 0.2 7.3 nd nd nd Trace nd – 8.3

0.9 2.5 ± 0.1 nd 1.9 ± 0.1 0.6 0.2 5.2 0.7 nd nd Trace Trace 0.7 6.8

0.2 0.1 1.2 ± 0.1 nd nd 0.1 1.4 0.3 0.1 1.6 0.3 1.5 3.8 5.4

– 0.2 0.8 1.9 ± 0.1 nd 0.3 3.2 0.2 Trace 3.3 ± 0.1 Trace 1.3 4.8 8.0

– 1.0 ± 0.1 3.6 ± 0.2 nd 2.2 ± 0.1 0.3 7.1 nd nd nd Trace nd – 7.1

0.7 1.8 ± 0.1 1.3 ± 0.1 nd 0.6 0.3 4.0 0.3 0.08 nd Trace 0.2 0.6 5.3

1.5 6.5 ± 0.1 2.4 nd 2.2 0.2 11.3 nd nd nd Trace nd – 12.8

2.4 4.3 ± 0.4 4.2 ± 0.4 nd 1.9 ± 0.1 0.3 10.7 nd Trace nd Trace nd – 13.1

nd = not detected.

previous work (Fratianni, Tucci, De Palma, Pepe, & Nazzaro, 2007; Lombardo et al., 2010), presumably related to their different roles. In particular, the flavonoids can protect leaf cells from photooxidative damage from excess ultraviolet (UV) light, especially its B component (280–320 nm), amongst other functions (Jaakola, Määttä-Riihinen, Kärenlampi, & Hohtola, 2004; Smith & Markham, 1996). Since the leaf is the most sun-exposed organ, the plant stimulates two flavonoid biosynthetic enzymes, chalcone synthase

(CHS) and chalcone isomerise (CHI), rather than those involved in the caffeoylquinic acid biosynthesis (Fig. 1) (Broschè & Strid, 2003). In contrast, the biosynthesis of caffeoylquinic acids might be up-regulated on the floral stem, due to its role of mechanical support of immature inflorescences of C. cardunculus. In fact, these compounds have been implicated in providing structural support for the plant cell-wall by bridging certain polymeric cell-wall compounds, such as polysaccharides (Faulds & Willimason, 1999). This

420


Table 2 Phenolic content (g kg

1

of DM) of C. cardunculus floral stem in relation to genotype.

Compound

Genotype

1-Caffeoylquinic acid 3-Caffeoylquinic acid 5-Caffeoylquinic acid 3,5-Dicaffeoylquinic acid 1,5-Dicaffeoylquinic acid Monosuccinyldicaffeoylquinic acid Monosuccinyldicaffeoylquinic acid Total caffeoylquinic acid Luteolin rutinoside Luteolin glucoside Luteolin glucuronide Luteolin malonylglucoside Luteolin Total luteolin Apigenin rutinoside Apigenin glucoside Apigenin glucuronide Apigenin malonylglucoside Apigenin Total apigenin Total measured polyphenols

Altilis

Cimiciusa

Blanc Hyèrois

Nobre

Sylvestris Creta

Sylvestris Kamaryna

Tempo F1

Tondo di Paestum

Tema 2000

Violetto di Sicilia

nd 0.3 8.7 ± 0.2 nd 6.2 ± 0.2 1.4 ± 0.1

nd nd 0.9 ± 0.1 0.09 4.6 ± 0.5 nd

nd nd 2.5 ± 0.2 0.04 1.2 ± 0.1 nd

Trace Trace 5.1 ± 0.2 nd 7.9 ± 0.4 0.04

nd nd 4.3 ± 0.1 nd 13.3 ± 0.4 0.08

nd nd 2.4 ± 0.1 nd 3.4 ± 0.3 nd

nd nd 2.0 ± 0.2 nd 0.9 ± 0.1 nd

nd Trace 2.1 ± 0.2 Trace 1.2 ± 0.1 nd

Trace Trace 2.1 ± 0.2 0.07 2.4 ± 0.2 nd

nd nd 13.3 ± 0.2 0.08 6.3 ± 0.2 nd

0.4

0.4

Trace

Trace

Trace

Trace

nd

nd

nd

nd

17.0 nd 0.3 0.5 nd 0.08 0.9 nd nd nd 0.4 0.2 0.6 18.5

6.0 0.1 0.6 ± 0.1 nd nd 0.8 ± 0.1 1.5 nd nd 2.8 ± 0.2 0.8 ± 0.1 1.1 ± 0.1 4.7 12.2

3.7 0.2 0.2 nd 0.1 Trace 0.5 nd nd nd nd nd – 4.2

13.0 0.2 0.2 nd 0.2 Trace 0.6 nd nd nd 0.3 Trace 0.3 13.9

17.7 nd 0.4 nd nd 0.1 0.5 nd nd 0.4 nd nd 0.4 18.6

5.8 0.3 1.4 ± 0.1 nd 1.2 0.1 3.0 nd nd nd Trace Trace – 8.8

2.9 0.5 0.4 nd 0.3 0.04 1.2 nd nd nd nd nd – 4.1

3.3 0.2 0.1 nd nd 0.03 0.3 nd nd 0.1 nd Trace 0.1 3.7

4.5 0.2 0.08 nd nd 0.02 0.3 nd nd 0.2 Trace Trace 0.2 5.0

19.6 0.3 0.3 nd 0.3 0.06 1.0 nd nd nd nd nd – 20.6

nd = not detected.

Table 3 Ferric reducing-antioxidant power (FRAP) of C. cardunculus extracts at 4 and 60 min. Genotype

Floral stem a

Altilis Cimiciusa Blanc Hyèrois Nobre Sylvestris Creta Sylvestris Kamaryna Tempo F1 Tondo di Paestum Tema 2000 Violetto di Sicilia a

Rank

Leaf

Rank

FRAP value 4 min

20.0 ± 2.0 3.7 ± 0.3 5.9 ± 0.6 15.3 ± 1.4 16.5 ± 0.5 7.3 ± 0.5 4.7 ± 0.4 4.1 ± 0.4 6.5 ± 0.6 18.9 ± 1.9

Values are expressed as mmol Fe2+ kg

1 10 7 4 3 5 8 9 6 2 1

Floral stem

Rank

Leaf

Rank

1 10 7 4 3 5 8 9 6 2

5.3 ± 0.6 – 12.3 ± 1.1 10.8 ± 1.1 5.9 ± 0.2 5.0 ± 0.5 11.2 ± 1.2 5.6 ± 0.5 19.1 ± 1.9 16.8 ± 1.3

8 – 3 5 6 9 4 7 1 2

FRAP value 60 min 4.2 ± 0.4 – 9.5 ± 0.6 6.1 ± 0.5 3.9 ± 0.1 4.2 ± 0.4 7.5 ± 0.8 4.8 ± 0.4 12.4 ± 1.1 10.7 ± 1.0

8 – 3 5 6 9 4 7 1 2

31.0 ± 3 5.2 ± 0.5 8.6 ± 0.8 22.7 ± 2.1 24.8 ± 0.9 17.7 ± 1.8 7.5 ± 0.6 7.0 ± 0.7 10.2 ± 1.0 28.4 ± 2.3

of DM.

cross-linking leads to a strong plant cell-wall and affects certain cell-wall parameters, such as extensibility (Faulds & Willimason, 1999). Moreover, they are precursors of lignin, involved in enhancing mechanical defence of the plant cell-wall (Fig. 1). The genetic background of the genotypes of C. cardunculus analysed affected the phenolic profile. ‘Violetto di Sicilia’ showed the highest total measured polyphenol content in the floral stem and leaf (21 and 13 g kg 1 of DM, respectively) (Tables 1 and 2). This genotype, as well as the others of globe artichoke studied, showed luteolin derivatives as the main compounds in leaves, whereas in ‘Altilis’ (cultivated cardoon), ‘Sylvestris Kamaryna’ and ‘Sylvestris Creta’ (wild cardoons), apigenin derivatives were the most abundant (56, 48 and 38 g kg 1 of DM, respectively) (Table 1). This suggests that the leaf of cardoon forms may be less sensitive to UV light than leaf of globe artichoke, since apigenin derivatives (monohydroxyflavones) are less effective free radical scavengers and at dissipating absorbed UV energy than luteolin derivatives (dihydroxyflavones) (Fig. 1) (Smith & Markham, 1996). In the floral stem, ‘Altilis’ contained two monosuccinyldicaffeoylquinic acids (m/z 615), already reported in leaf of C. cardunculus (Pinelli et al., 2007) but not in the floral stem, whereas

‘Sylvestris Creta’ and ‘Violetto di Sicilia’ had the highest 1,5-dicaffeoylquinic acid (13 g kg 1 of DM) and chlorogenic acid (13 g kg 1 of DM) content, respectively, amongst all genotypes studied (Table 2). In contrast, the highest total apigenin content is in the floral stem of ‘Cimiciusa di Mazzarino’ (47 g kg 1 of DM) (Table 2). In the leaf and floral stem, a new compound was identified as apigenin-malonylglucoside on the basis of its UV spectrum and mass spectrometric fragmentation, in the leaf and the floral stem; this compound has been previously reported in capitula of C. cardunculus (Pandino, Courts, Lombardo, Mauromicale, & Williamson, 2010). The highest amounts were found in the leaf of ‘Altilis’ (0.4 g kg 1 of DM) and in the floral stem of ‘Cimiciusa di Mazzarino’ (0.8 g kg 1 of DM) (Tables 1 and 2). 3.2. Evaluation of the antioxidant capacity using FRAP assay The FRAP assay is commonly used for measuring the total antioxidant capacity of extracts of foods and plants. This method is based on the ability of antioxidants to reduce Fe3+–Fe2+ and measures directly the reducing capacity of the substance (Benzie & Strain, 1996). In contrast, other antioxidant assays measure the

FRAP value (mmol Fe 2+ kg-1 of Dm)


FRAP value4min 18 16 14 12 10 8 6

quinic acids and luteolin derivatives. In relation to the fraction of the plant, the antioxidant capacity of the floral stem was higher than the leaf (Fig. 2). It was found that the antioxidant capacity of the leaf was significantly and positively correlated (r = 0.97, P 6 0.001) with luteolin content, whereas, in the floral stem, it was strongly and positively correlated (r = 0.95, P 6 0.001) with the content of caffeoylquinic acids, which were the main compounds in the leaf and floral stem, respectively (Fig. 3).

FRAP value60min

A

B

421

a

b

4 2

4. Conclusion

0 Lea f

Stem

Fig. 2. Antioxidant capacity of C. cardunculus in relation to the fraction of the plant. Values are the mean of measurements on genotypes. Different letters indicate significance at P 6 0.05.

inhibition of reactive species (free radicals) generated in the reaction mixture and, thus, results also depend on the type of reactive species used (Halvorsen et al., 2002). The FRAP values at 4 and 60 min of extracts of leaf and floral stem are summarised in Table 3. Amongst the genotypes tested, the floral stem of ‘Altilis’ (cultivated cardoon) had the highest FRAP value4min (20.0 mmol Fe2+ kg 1 of DM), followed by ‘Violetto di Sicilia’ (18.9 mmol Fe2+ kg 1 of DM). In contrast, the leaf of ‘Altilis’, as well as ‘Sylvestris Kamaryna’ and ‘Sylvestris Creta’ (both wild cardoons) showed the lowest content (4.2, 4.2 and 3.9 mmol Fe2+ kg 1 of DM, respectively). Probably these results were affected by the presence of apigenin derivatives in the leaf of cardoon forms. In fact, these compounds are poorly active in the FRAP assay (Firuzi et al., 2005) compared to caffeoyl-

The leaf and floral stem, usually considered as waste, could have an added economic benefit through extraction of natural antioxidants. In particular, the leaf is rich in luteolin derivatives, whereas the floral stem is a good source of caffeoylquinic acids. In addition, the leaves of cardoon forms have a high content of apigenin derivatives. Although the interpretation of data from the FRAP assay is complicated, the antioxidant capacity of extracts was strongly dependent on the qualitative and quantitative phenolic profile. However, it cannot be ruled out that other non-phenolic compounds might be involved in the antioxidant activity (Plumb et al., 1996). For exploitation of natural antioxidants, the use of leaf of ‘Tema 2000’ and ‘Violetto di Sicilia’ is suggested, as well as the floral stem of ‘Violetto di Sicilia’, ‘Nobre’, ‘Cimiciusa di Mazzarino’, ‘Sylvestris Kamaryna’ and ‘Altilis’, for their high total measured polyphenols content. However, the mixture of leaf and floral stem could be used to guarantee a wide range of phenolic compounds. In this study, we report, for the first time, the phenolic composition of the floral stem of wild and cultivated cardoon.

-1

Phenolic compounds (g kg of DM)

Acknowledgement

TOT CQA

25

-1

This research was partially supported by the CAR-VARVI project (MiPAF).

***

r = 0.95 20

References

15

Beckman, C. H. (2000). Phenolic-storing cells: Keys to programmed cell death and periderm formation in wilt disease resistance and in general defence responses in plants? Physiological and Molecular Plant Pathology, 57, 101–110. Benzie, I. F., & Strain, J. J. (1996). The ferric reducing ability of plasma (FRAP) as a measure of ‘‘antioxidant power’’: The FRAP assay. Analytical Biochemistry, 239, 70–76. Berardini, N., Knödler, M., Schieber, A., & Carle, R. (2005). Utilization of mango peels as a source of pectin and polyphenolics. Innovative Food Science and Emerging Technologies, 6, 442–452. Brat, P., Georgè, S., Bellamy, A., Du Chaffaut, L., Scalbert, A., Mennen, L., et al. (2006). Daily polyphenol intake in France from fruit and vegetables. The Journal of Nutrition, 136, 2368–2373. Broschè, M., & Strid, A. (2003). Molecular events following perception of ultravioletB radiation by plants. Plant Physiology, 117, 1–10. Carle, R., Keller, P., Schieber, A., Rentschler, C., Katzschner, T., Rauch, et al. (2001). Method for obtaining useful materials from the by-products of fruit and vegetable processing. Patent Application WO 01/78859 A1. Choi, H. S., Song, L. S., Ukeda, L., & Sawamura, M. (2000). Radical-scavenging activities of citrus essential oils and their components: Detection using 1, 1diphenyl-2-picrylhydrazyl. Journal of Agricultural and Food Chemistry, 48, 4156–4161. Faulds, C. B., & Willimason, G. (1999). The role of hydroxycinnamates in the plant cell wall. Journal of the Science of Food and Agriculture, 79, 393–395. Firuzi, O., Lacanna, A., Petrucci, R., Marrosu, G., & Saso, L. (2005). Evaluation of the antioxidant activity of flavonoids by ‘‘ferric reducing antioxidant power’’ assay and cyclic voltammetry. Biochimica et Biophysica Acta, 1721, 174–184. Fratianni, F., Tucci, M., De Palma, M., Pepe, R., & Nazzaro, F. (2007). Polyphenolic composition in different parts of some cultivars of globe artichoke (Cynara cardunculus L. var. scolymus (L.) Fiori). Food Chemistry, 104, 1282–1286. Halvorsen, B. L., Holte, K., Myhrstad, M. C. W., Barikmo, I., Hvattum, E., Remberg, S. F., et al. (2002). A systematic screening of total antioxidants in dietary plants. The Journal of Nutrition, 132, 461–471. Jaakola, L., Määttä-Riihinen, K., Kärenlampi, S., & Hohtola, A. (2004). Activation of flavonoid biosynthesis by solar radiation in bilberry (Vaccinium myrtillus L.) leaves. Planta, 218, 721–728. Lattanzio, V., Cicco, N., Terzano, R., Raccuia, S., Mauromicale, G., Di Venere, D., et al. (2002). Potenziale utilizzo di sottoprodotti derivanti dalla lavorazione

10 5

r = -0.13

ns

0 0

5

10

15

FRAP value (mmol Fe

Phenolic compounds (g kg of DM)

FLORAL STEM

TOT LUT

TOT CQA

2+

20

25

-1

kg of DM)

TOT LUT

***

12

r = 0.97

10 LEAF

8 6 4

*

r= 0.78

2 0 0

5 FRAP value (mmol Fe

10 2+

15

-1

kg of DM)

Fig. 3. Correlation coefficient (r) between phenolic compounds (g kg 1 of DM), total caffeoylquinic acids (TOT CQA) and luteolin derivatives (TOT LUT), and antioxidant capacity (mmol Fe2+ kg 1 of DM). ns, and indicate not significant and significant at P 6 0.05 and 0.001, respectively.

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