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Chemical composition and antioxidant properties of mature and baby artichokes (Cynara scolymus L.), raw and cooked
Journal of Food Composition and Analysis 24 (2011) 49–54
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Original Article
Chemical composition and antioxidant properties of mature and baby artichokes (Cynara scolymus L.), raw and cooked M. Lutz a,b,*, C. Henrı´quez a,b, M. Escobar c a
Centro de Investigacio´n y Desarrollo de Alimentos Funcionales, CIDAF, Facultad de Farmacia, Universidad de Valparaı´so, Gran Bretan˜a 1093, Valparaı´so, Chile Centro Regional de Estudios en Alimentos Saludables CREAS, Gran Bretan˜a 1093, Valparaı´so, Chile c Departamento de Bioquı´mica, Facultad de Farmacia, Universidad de Valparaı´so, Gran Bretan˜a 1093, Valparaı´so, Chile b
A R T I C L E I N F O
A B S T R A C T
Article history: Received 10 March 2010 Received in revised form 7 June 2010 Accepted 12 June 2010 Available online 30 July 2010
Artichoke is a traditionally consumed vegetable in many countries. In the past decade, the immature (baby) variety has been successfully introduced in the international food markets. The aim of this study is to compare the chemical composition and antioxidant properties of mature and baby artichokes, in raw state and after cooking. For this purpose, the proximate chemical analysis was estimated, and aqueous and hydroalcoholic extracts were obtained to determine the contents of total polyphenols, caffeic acid, chlorogenic acid, and cynarin. Proximate analysis revealed that cooking increased proteins and lipids in baby artichokes (p < 0.05). The total phenolics content was similar in mature and baby artichokes and increased after cooking (p < 0.05). Cooked baby artichokes exhibited the highest total phenolics, caffeic acid, chlorogenic acid, and cynarin contents, as well as free radical scavenging capacity, measured as DPPH. Our results show that baby artichokes exhibit higher scavenging capacity than mature artichokes, and thus they constitute a particularly interesting source of putative antioxidant polyphenols, a quality that is improved by the application of thermal treatment. ß 2010 Elsevier Inc. All rights reserved.
Keywords: Artichoke Cynara scolymus L. Maturity Cooking Antioxidant capacity Polyphenols Chemical composition Food analysis Food composition
1. Introduction Artichoke (Cynara scolymus L.) is widely cultivated in the Mediterranean regions and adjoining parts of Europe, which accounts for 85% of the world’s production. The production and intake of this vegetable is increasing in South America, where it has been cultivated for over a century. The traditional form of intake is the cooked mature head, and in the last past few years the immature baby artichokes (BA) have been successfully introduced in the market. Globe artichoke is considered a healthy food due to its nutritional and phytochemical composition. It contains proteins, minerals, a low amount of lipids, dietary fiber and a high proportion of phenolics (Llorach et al., 2002; Fratianni et al., 2007). The phenolics include cynarin (1,3-di-O-caffeoylquinic acid), luteolin, cynaroside (luteolin-7-O-glucoside), scolymoside (luteolin-7-rutinoside); phenolic acids such as caffeic, coumaric, hydroxycinnamic, ferulic, caffeoylquinic acid derivatives; mono- and dicaffeoylquinic acids, including chlorogenic; acid alcohols; flavonoid glycosides, among others
* Corresponding author at: Centro de Investigacio´n y Desarrollo de Alimentos ˜a Funcionales, CIDAF, Facultad de Farmacia, Universidad de Valparaı´so, Gran Bretan 1093, Valparaı´so, Chile. Tel.: +56 322508418; fax: +56 322508111. E-mail addresses: [email protected], [email protected] (M. Lutz). 0889-1575/$ – see front matter ß 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.jfca.2010.06.001
(Sa´nchez Rabaneda et al., 2003; Fratianni et al., 2007). Artichokes exhibit a high antioxidant capacity expressed as ORAC (Wu et al., 2004), and Halvorsen et al. (2006) placed it as number 17 in the ranking of the 50 foods with the highest antioxidant content, reaching the fourth place when the antioxidant content is expressed in terms of the serving size. The content of phenolics varies among different cultivars, age, generation of the plant, growing conditions, harvest, post-harvest and storage conditions, and the technological procedures used (Toma´s-Barbera´n and Espı´n, 2001). Several studies have reported that boiling vegetables induces the loss of nutrients and bioactive compounds that are unstable to heat. In general, it is considered that cooked vegetables have a lower health-promoting effect than the corresponding raw ones. The rationale for this has traditionally been based on the measurement of selected barely stable antioxidants of nutritional interest (e.g. ascorbic acid) commonly assessed as indicators of the processing damage (Nicoli et al., 1999; Dewanto et al., 2002a,b). Since artichokes are usually cooked before eating, it is important to evaluate the effect of cooking on some nutrients and antioxidant phenolics. There is no report discussing the changes in the contents of various health-promoting phenolics in artichokes that additionally takes into consideration the effects of the stage of maturity of this vegetable. The aim of this study was to obtain data on commonly consumed artichokes, and to compare the chemical composition and
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antioxidant content and activity between mature and immature edible heads. In addition, the effect of cooking on the chemical composition of mature and BA is also described, especially because the data on changes of these compounds during this processing are still limited and sometimes contradictory. 2. Materials and methods 2.1. Materials Artichokes (cv. Green Globe) were grown under typical conditions of soil, irrigation, and illumination in Melipilla, 60 km Southwest from Santiago, Chile. Fifty artichokes, mature and in an early stage of maturity (BA), with an approximate diameter of 11 cm (mature) and 4.5 cm (baby) were manually and randomly picked across the field in December (Summer) of 2008. They were placed in polyethylene bags and transported at 4 8C to the laboratory. Samples were then selected to eliminate damaged and poor quality units and to obtain uniformity. The samples were stored in a refrigerated chamber at 4 8C until extraction and analysis. Sample preparation: Mature sample stems were cut 2 cm below the base of the bud, and BA stems were removed 1 cm below the base of the bud. Mature and BA heads were manually sorted and randomly separated according to their size into two groups, one to be cooked in boiling water (n = 6) and the other to be kept raw (n = 6). Artichoke heads were cooked in boiling water under pressure in a covered pressure 4 L capacity pot for 10 min. Samples were immediately cooled in cold water and drained. Both cooked and raw samples were dried in an oven at 50 8C for 5 days (Asami et al., 2003), ground, sealed in polypropylene bags, and stored at 4 8C until analysis. All measurements were performed by triplicate. 2.2. Chemicals All reagents and solvents were analytical grade chemicals from Merck (Darmstadt, Germany) or Sigma Chemical Co. (St. Louis, MO, USA). 2.3. Proximate analysis Protein content was determined by Kjeldahl (AOAC 920.54) using a factor of 6.25. Crude fat was assessed using the AOAC method 920.39, moisture was assessed using the AOAC method 945.15, and ash was determined using the AOAC method 942.05 (AOAC, 2006). Dietary fiber was measured as described by Lee et al. (1992) and total carbohydrates were estimated by difference (meaning 100 the sum of moisture, protein, fat and ash). 2.4. Preparation of extracts Aqueous (AE) and hydroalcoholic (HE) (ethanol:water 1:1) extracts of mature and BA (raw and boiled) were prepared. To obtain the AE, 5.5 g of each powdered plant material were macerated for 15 min in 30 mL water at room temperature, and 30 mL boiling water were added and kept under continuous stirring for 5 min at 50–70 8C. After cooling at room temperature, the extracts were filtered through glass wool and paper (5A and 131) and taken to a final volume of 100 mL with water. The HE was prepared weighing 5.5 g of each powdered sample, and 60 mL ethanol:water (1:1) was added. The mixture was heated under reflux at 100 8C for 5 min. After cooling at room temperature, the extracts were filtered through glass wool and paper (5A and 131) and taken to a final volume of 100 mL with ethanol:water (1:1). Both extracts were stored in amber vials at 4 8C until analysis.
2.5. Total phenolics (TP) A quantity of 1 mL of each extract was taken to a final volume of 10 mL with water (AE) or ethanol:water (1:1) (HE) and measured by the non-specific colorimetric reaction with the Folin Ciocalteu reagent that measures the reducing capacity of the samples (Singleton and Rossi, 1965) in a spectrophotometer (Perkin Elmer Lambda EZ 201, Norwalk, CT, USA). The measurement was compared to a standard curve prepared with tannic acid in the range 2.5–15 mg tannic acid/100 mL. TP content was expressed as mg of tannic acid equivalents (TAE) per 100 g dry sample. 2.6. Antioxidant activity by free radical scavenging of DPPH Then 50 mL of each extract, previously filtered (0.22 mm), were added 2 mL DPPH (diphenylpicrylhydrazyl) 6 10 5 M in methanol (Molyneaux, 2004). Both AE and HE were measured spectrophotometrically (Perkin Elmer Lambda EZ 201, Norwalk, CT, USA). Absorbance was measured at 517 nm during 16 min using methanol as blank. The antioxidant capacity was expressed as a percentage of inhibition of DPPH radical (% inhibition of DPPH radical) calculated according to the following equation: % inhibition of DPPH radical = [(AC(0) AA(t))/AC(0)] 100, where AC(0): absorbance of the control at time = 0 min; and AA(t): absorbance of the antioxidant at time = 16 min. 2.7. Caffeic acid, chlorogenic acid, and cynarin The HE of raw and boiled artichokes (mature and BA) were centrifuged at 1800 g for 15 min at 20 8C and concentrated with methanol:water (1:1) in a rotary evaporator under reduced pressure at 65 8C. After concentration and filtration (0.22 mm) the polyphenols were measured using a Merck-Hitachi Lachrom HPLC (Merck–Hitachi, Frankfurt–Tokyo, Germany–Japan) equipped with a quaternary pump programmable for gradients, thermostatic controlled column chamber, rheodyne injection valve with a 100 mL sample loop, and UV–visible detector at 326 nm. The column employed was C-18 Lichrospher column (250 mm 4.0 mm, 5 mm), fitted with suitable guard column. The mobile phase was a mixture of (A): H2O adjusted to pH 2.4 with 99% CH3COOH, and (B): CH3CN. The following descendent gradient of solvents was applied: 92% A and 8% B to 30% A and 70% B in 50 min (flow: 0.4 mL/min at 30 8C). Calibration curves were prepared for chlorogenic acid (5–80 mg/L), caffeic acid (0.1– 1.8 mg/L) and cynarin (5–50 mg/L), using the corresponding standards purchased from Sigma Chemical Co. (St. Louis, MO). The analyses were run with six repetitions. 2.8. Statistical analysis The analyses were performed in triplicate; each replicate was quantified in duplicate, unless stated otherwise. All data given represent mean values standard error (SE). Data were processed by two-way analysis of variance (ANOVA) and statistical significance by Student’s t-test. All statistical analysis and correlations were made with SAS1. p < 0.05 was considered significant. We studied the effect of cooking by comparing raw and boiled artichokes and the effect of maturity by comparing the fully grown and BA. 3. Results and discussion 3.1. Effect of cooking on chemical composition The chemical composition of mature and BA (raw and cooked) is reported in Table 1. The moisture content ranged between 76.6 (raw, mature) and 86.2 (BA, cooked) g/100 g f.w., depending on the
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Table 1 Means and standard error of the chemical composition of mature and baby artichokes, raw or cooked (g/100 g) (n = 6). Mature raw Moisture (f.w.) Ash (d.w.) Crude fat (d.w.) Protein (d.w.) Total carbohydrates Dietary fiber (d.w.)
76.60 0.46 7.04 0.05* 1.15 0.15 15.96 0.18 75.85 0.17 65.82 0.30*
Mature cooked *
80.94 0.02 6.70 0.02 1.76 0.13 17.71 0.18 73.84 0.73 63.69 0.46
Baby raw
Baby cooked
81.24 0.08 7.17 0.41 2.36 0.08 12.29 0.10 78.18 0.43* 64.78 0.27*
86.22 0.35* 7.63 0.20 3.47 0.19* 14.45 0.16* 74.45 0.16 59.95 1.33
f.w.: fresh weight; d.w: dry weight. * Values in the same type of parameter and stage of maturity differ significantly (p < 0.05).
maturity and the processing (p < 0.05). As expected, these values increased after cooking, due to water absorption (Pellegrini et al., 2009; Pereira Lima et al., 2009). The ash content of artichokes ranged from 6.7 to 7.6 g/100 g d.w. Ash was higher in BA, but this difference was significant in the cooked samples only (p < 0.05). Mature artichokes exhibited 4.8% less ash content after cooking, while it increased in BA samples by 6.4%. Some minerals probably leached into the cooking water causing a reduction in the ash content. Total lipids varied between 1.15 and 3.47 g/100 g d.w. All samples increased their lipid content after cooking (53% and 47% in mature and BA, respectively), although this difference was significant in BA only (p < 0.05). These changes may be due to a higher extraction of released lipids (Pereira Lima et al., 2009). The total lipid content was significantly higher in the BA (p < 0.05). The crude protein content ranged from 12.3 (raw BA) to 17.7 g/ 100 g d.w. (cooked mature samples). Protein increased by 10.9% in mature and 17.5% in BA after cooking (p < 0.05 in BA only). This is in disagreement with Pereira Lima et al. (2009), who reported a decrease of the protein content in some cooked vegetables. These authors observed different effects of cooking on different vegetables (e.g. in Chinese cabbage cooking induced an increase of sample water content and lipids and a decrease in total protein). The conformation of the vegetable matrix is likely the determinant factor ruling their ability to retain/degrade components affecting the global proximate chemical composition. Carbohydrates ranged from 73.8 to 78.2 mg/100 g d.w. BA contained higher amounts of carbohydrates (p < 0.05), independently of the processing. Total carbohydrates decreased after cooking (by 4.8% in BA and 2.7% in mature artichokes). The loss in BA (p < 0.05) is attributed to the leak of these compounds into the water. The total dietary fiber ranged from 60.0 to 65.8 mg/100 g d.w. In both stages of maturity, cooking decreased the dietary fiber content (by 7.5% in BA and 3.2% in mature samples). The loss may be related with the thermal degradation of polysaccharides, as well as the solubilization of constituents that leak into the water (Svanberg et al., 1997). Cooking may alter the properties of fiber, and changes in total fiber content as well as in extractability have been reported, leading to redistribution between the relative amounts of soluble and insoluble fractions (Puupponen-Pimia¨ et al., 2003).
Table 2 shows that TP in the AE of raw artichokes (mature and BA) contained 5.4 and 4.6 mg TAE/100 g d.w., respectively, while in the HE the values were 5.8 and 5.9 mg TAE/100 g d.w. This indicates that TP in the AE were dependent on the maturity and the thermal processing (p < 0.05). TP in the AE of raw mature samples were 1.2 higher than those contained in BA, while they were similar in the HE, indicating that maturity does not affect these phenolics. Studies performed on different cooked vegetables have reported that TP vary depending on the treatment. They may decrease up to 50% due to antioxidant breakdown and leaking into the water (Gil et al., 1999), may increase due to a higher accessibility (Dewanto et al., 2002a; Puupponen-Pimia¨ et al., 2003; Choi et al., 2006), or may remain unchanged (Oboh, 2005; Sultana et al., 2008; Pellegrini et al., 2009). After cooking, TP content in the AE of mature and BA were 11.9 and 23.4 mg TAE/g d.w., while in the HE the values for mature and BA were 8.1 and 17.4 mg TAE/g d.w., respectively. TP were higher in the extracts obtained from the cooked samples (mature and BA), mainly in the aqueous form, probably due to the high amount of hydrosoluble phenolics, as flavonoids (Wang et al., 2003). The increase after cooking (over 50%) in the AE may also reflect the release of derivatives by hydrolysis. In addition, the increase was higher in BA (between 5.1- and 2.9-fold in the AE and HE, respectively), proving that the thermal processing enhances their potentially healthy value. Additionally, this result may also be at least partially explained by the lack of selectivity of the Folin Ciocalteu method used to measure TP, thus generating overestimated values (Prior et al., 2005; Huang et al., 2005). In agreement with our results, other authors have reported higher TP in artichokes and by-products after water blanching (Llorach et al., 2002; Schu¨tz et al., 2004). The increase may be partly due to a release of bound phenolic acids and the breakdown or softening of cellular constituents of plant cells, leading to augmented accessibility of the antioxidants. These complex compounds may be more easily released in relation to those found in the raw plants, improving their antioxidant capacity. In addition, cooking may cause the breakage of complex structures liberating individual phenolics and/or phenolic degradation products which could also react with the Folin-Ciocalteu reagent (Dewanto et al., 2002a,b; Turkmen et al., 2005; Choi et al., 2006; Sultana et al., 2008). As heating deactivates oxidative enzymes, it also prevents the enzymatic oxidation that causes the loss of
3.2. Effect of cooking on phenolics Cooking vegetables in boiling water is traditionally associated with a reduction of nutritional properties and loss of antioxidants due to oxidation, thermal degradation, leaching and other events that reduce these compounds (Amin and Lee, 2005; Gawlik-Dziki, 2008; Pellegrini et al., 2009). Since it is currently accepted that phenolics are the major contributors to the antioxidant activity of plant foods, it is important to evaluate not only the impact of the stage of maturity, but also the effect of the heat treatment on the TP in artichoke extracts.
Table 2 Means and standard error of the total phenolics concentration of extracts obtained from raw or cooked mature and baby artichokes (mg tannic acid equivalents/100 g sample) (n = 6). Extract
Mature raw
Mature cooked
Baby raw
Baby cooked
AE HE
5.40 0.13 5.76 0.09
11.93 0.30* 8.12 0.05*
4.55 0.14 5.93 0.15
23.38 0.57* 17.40 0.30*
AE: aqueous extract; HE: hydroalcoholic extract. * Values in the same type of extract and stage of maturity differ significantly (p < 0.05).
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Table 3 Means and standard error of the antioxidant capacity of extracts obtained from raw or cooked mature and baby artichokes (% inhibition of DPPH radical) (n = 6). Extract
Mature raw
Mature cooked
Baby raw
Baby cooked
AE HE
30.50 0.14 28.46 0.33
29.60 1.28 34.56 0.63*
5.02 0.17 22.97 0.39
61.26 0.09* 69.91 0.01*
AE: aqueous extract; HE: hydroalcoholic extract. * Values in the same type of extract and stage of maturity differ significantly (p < 0.05).
antioxidants in raw materials. Artichokes are a good source of polyphenol oxidases (PPO) that catalyze the oxidation of phenolics to quinones that subsequently induce the formation of secondary products (Espı´n et al., 1997). PPO may reduce TP in raw artichokes, and since heating inactivates PPO, it enables their preservation. Similar results have been reported in other vegetables (Talcott et al., 2000; Dewanto et al., 2002a,b; Oboh, 2005; Turkmen et al., 2005; Choi et al., 2006; Sultana et al., 2008; Pereira Lima et al., 2009). However, other researchers have reported that cooking reduces TP (Gil et al., 1999; Puupponen-Pimia¨ et al., 2003; Zhang and Hamauzu, 2004; Turkmen et al., 2005; Gliszczyn´ska-S´wiglo et al., 2006; Sultana et al., 2008; Volden et al., 2009). Clearly, the TP content may vary widely due to agricultural factors and processing (Oboh, 2005). The results are also affected by the analytical methodologies and the variety of the phenolics, ranging from simple to very complex molecules. 3.3. Effect of cooking on antioxidant capacity Table 3 shows the capacity of the aqueous and hydroalcoholic extracts to inhibit the DPPH radical at 16 min. The antioxidant capacities of the AE in raw mature and BA were 30.5 and 5.0% inhibition of DPPH radical, respectively, while in the HE the values were 28.5 and 23.0% inhibition of DPPH radical. Thus, the property was dependent both on the maturity and the processing (p < 0.05). Cooking affected the antioxidant capacity of the AE obtained from mature artichokes to a lesser extent, since no differences were observed between raw and cooked samples. The extracts obtained from BA exhibited higher values after thermal treatment (p < 0.05). Cooking increased the antioxidant capacities of the extracts, by 12.2-fold in AE and 3.0-fold in HE, respectively, probably due to a less efficient extractive process in the more rigid mature specimens. On the contrary, in BA there was a more exhaustive extraction of antioxidants, due to the matrix softening and disruption that allowed their release (Pellegrini et al., 2009). The higher antioxidant activity observed in the HE may be partly attributed to the thermal process in alcohol as well, since it improves the efficacy of the extractive process (Mulinacci et al., 2004). This is in agreement with several reports on artichokes and by-products (Llorach et al., 2002; Mulinacci et al., 2004; Jime´nezMonreal et al., 2009; Pellegrini et al., 2009) and other vegetables (Dewanto et al., 2002a,b; Turkmen et al., 2005; Choi et al., 2006; Miglio et al., 2008; Sultana et al., 2008). Many reports indicate that the antioxidant capacity of raw vegetables is higher (Puupponen-Pimia¨ et al., 2003; Wang et al., 2003; Zhang and Hamauzu, 2004; Mulinacci et al., 2004; Gawlik-
Dziki, 2008; Sultana et al., 2008; Volden et al., 2009; Faller and Fialho, 2009), while the antioxidant activity of some vegetables such as squash, peas and leek after cooking remained unchanged (Turkmen et al., 2005). These differences may be explained by the variety of vegetable species and processing methods used. We observed that cooking artichokes in boiling water increased their antioxidant content and activity. In agreement with our data, Ferracane et al. (2008) observed an increase of the total antioxidant capacity values in cooked samples with respect to raw artichokes, independently of the assay used, stating that the spatial arrangement of the phenolic groups can deeply affect the antioxidant activity of the molecules. Different mechanisms have been described to explain similar findings (Volden et al., 2009; Jime´nez-Monreal et al., 2009). In spite of the shortcomings of the Folin Ciocalteu method and the interpretation of the results as TP (Prior et al., 2005; Huang et al., 2005), our study clearly demonstrates that, mainly in immature samples, home cooking can ameliorate the TP content, suggesting that the real intake of these phytochemicals can be underestimated when using data from raw artichokes (Faller and Fialho, 2009). Literature reports on the relationship between TP and the antioxidant capacity are contradictory, and only few high correlations have been observed (Llorach et al., 2002; Wang et al., 2003). The correlation coefficients between TP content and antioxidant capacity of artichokes (BA and mature) demonstrate a strong, positive correlation between these two parameters (p < 0.05). In addition, other non-phenolic compounds, such as antioxidant nutrients, may contribute to the antioxidant capacity of the samples. 3.4. Effect of cooking on polyphenols profile Table 4 shows the caffeic acid, chlorogenic acid and cynarin contents in the extracts obtained from mature and BA (raw or cooked). The phenolics analyzed were dependent on the degree of maturity and processing of the samples. Chlorogenic acid was the predominant phenolic species, followed by cynarin and caffeic acid. Cooking increased the content of caffeic acid 3.6- and 1.8-fold in BA and mature artichokes, respectively (p < 0.05). In addition, cooked BA exhibited the highest caffeic acid content (p < 0.05). Caffeic acid may be considered as a common representative of simple phenolics in vegetables. Caffeic acid content would be the result of monocaffeoylquinic and dicaffeoylquinic acids during processing, so although it may not be detected in fresh samples it may reach measurable amounts in by-products such as juice or pomace (Schu¨tz et al., 2004). Cynarin was at the range of 116.7– 238.2 mg/100 g d.w. It is noteworthy that in raw state mature artichokes contained more cynarin than BA. However, cooking duplicated the amount of cynarin in BA while it decreased by 1.1fold in mature samples. These results may be attributed to the isomerization of dicaffeoylquinic acid during the thermal treatment (Adzet and Puigmacia, 1985) and the esterification of caffeic acid, increasing the cynarin content. These molecular changes and the formation of new compounds are responsible for the increase of the antioxidant capacity observed in cooked artichokes (Kweon et al., 2001). The chlorogenic acid content was at the range of 112.7–456.3 mg/100 g d.w., revealing that it depends both on
Table 4 Means and standard error of the caffeic acid, chlorogenic acid and cynarin content in hydroalcoholic extracts obtained from raw or cooked mature and baby artichokes (mg/ 100 g) (n = 6). Phenol
Mature raw
Mature cooked
Baby raw
Baby cooked
Caffeic acid Cynarin Chlorogenic acid
0.82 0.04 183.46 3.09 184.93 3.77
1.45 0.07* 160.69 3.45* 210.68 2.82*
0.71 0.03 116.72 2.82 112.73 3.23
2.60 0.10* 238.21 6.39* 456.30 14.03*
*
Values in the same type of phenolic compound and stage of maturity differ significantly (p < 0.05).
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maturity and thermal processing (p < 0.05). Cooking increased chlorogenic acid by 1.1- and 4.0-fold in mature and BA, respectively. Mulinacci et al. (2004) attributed similar findings to isomerization and hydrolysis events, leading to a substantial redistribution of phenolic acids due to transesterification. In addition, Azzini et al. (2007) observed that chlorogenic acid, monocaffeoylquinic acids, cynarin and dicaffeoylquinic acids increased in mature heads after cooking. Ferracane et al. (2008) observed a significant increase of total caffeoylquinic acids, due to both isomerization and hydrolysis, highlighting the effect of transesterification. This is in agreement with our study, since we observed a steep increase of chlorogenic acid in cooked BA, confirming the increased extractability of these compounds in immature tissues in addition to the chemical changes previously described. We believe that immature tissues are softer, enabling the extractive processes to be more exhaustive. Therefore, the phenolics in BA extracts contributed to the significantly higher TP values, as shown in Table 2. This is also associated to a superior antioxidant capacity (Table 3). Furthermore, this is reinforced by the finding of increased comparative amounts of the three phenolics measured before and after thermal processing. It is difficult to attribute these results to one reason above others, but it is likely to be a combination of facts, among which chemical changes such as isomerization and hydrolysis are determinant.
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Journal of Food Composition and Analysis journal homepage: www.elsevier.com/locate/jfca
Original Article
Chemical composition and antioxidant properties of mature and baby artichokes (Cynara scolymus L.), raw and cooked M. Lutz a,b,*, C. Henrı´quez a,b, M. Escobar c a
Centro de Investigacio´n y Desarrollo de Alimentos Funcionales, CIDAF, Facultad de Farmacia, Universidad de Valparaı´so, Gran Bretan˜a 1093, Valparaı´so, Chile Centro Regional de Estudios en Alimentos Saludables CREAS, Gran Bretan˜a 1093, Valparaı´so, Chile c Departamento de Bioquı´mica, Facultad de Farmacia, Universidad de Valparaı´so, Gran Bretan˜a 1093, Valparaı´so, Chile b
A R T I C L E I N F O
A B S T R A C T
Article history: Received 10 March 2010 Received in revised form 7 June 2010 Accepted 12 June 2010 Available online 30 July 2010
Artichoke is a traditionally consumed vegetable in many countries. In the past decade, the immature (baby) variety has been successfully introduced in the international food markets. The aim of this study is to compare the chemical composition and antioxidant properties of mature and baby artichokes, in raw state and after cooking. For this purpose, the proximate chemical analysis was estimated, and aqueous and hydroalcoholic extracts were obtained to determine the contents of total polyphenols, caffeic acid, chlorogenic acid, and cynarin. Proximate analysis revealed that cooking increased proteins and lipids in baby artichokes (p < 0.05). The total phenolics content was similar in mature and baby artichokes and increased after cooking (p < 0.05). Cooked baby artichokes exhibited the highest total phenolics, caffeic acid, chlorogenic acid, and cynarin contents, as well as free radical scavenging capacity, measured as DPPH. Our results show that baby artichokes exhibit higher scavenging capacity than mature artichokes, and thus they constitute a particularly interesting source of putative antioxidant polyphenols, a quality that is improved by the application of thermal treatment. ß 2010 Elsevier Inc. All rights reserved.
Keywords: Artichoke Cynara scolymus L. Maturity Cooking Antioxidant capacity Polyphenols Chemical composition Food analysis Food composition
1. Introduction Artichoke (Cynara scolymus L.) is widely cultivated in the Mediterranean regions and adjoining parts of Europe, which accounts for 85% of the world’s production. The production and intake of this vegetable is increasing in South America, where it has been cultivated for over a century. The traditional form of intake is the cooked mature head, and in the last past few years the immature baby artichokes (BA) have been successfully introduced in the market. Globe artichoke is considered a healthy food due to its nutritional and phytochemical composition. It contains proteins, minerals, a low amount of lipids, dietary fiber and a high proportion of phenolics (Llorach et al., 2002; Fratianni et al., 2007). The phenolics include cynarin (1,3-di-O-caffeoylquinic acid), luteolin, cynaroside (luteolin-7-O-glucoside), scolymoside (luteolin-7-rutinoside); phenolic acids such as caffeic, coumaric, hydroxycinnamic, ferulic, caffeoylquinic acid derivatives; mono- and dicaffeoylquinic acids, including chlorogenic; acid alcohols; flavonoid glycosides, among others
* Corresponding author at: Centro de Investigacio´n y Desarrollo de Alimentos ˜a Funcionales, CIDAF, Facultad de Farmacia, Universidad de Valparaı´so, Gran Bretan 1093, Valparaı´so, Chile. Tel.: +56 322508418; fax: +56 322508111. E-mail addresses: [email protected], [email protected] (M. Lutz). 0889-1575/$ – see front matter ß 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.jfca.2010.06.001
(Sa´nchez Rabaneda et al., 2003; Fratianni et al., 2007). Artichokes exhibit a high antioxidant capacity expressed as ORAC (Wu et al., 2004), and Halvorsen et al. (2006) placed it as number 17 in the ranking of the 50 foods with the highest antioxidant content, reaching the fourth place when the antioxidant content is expressed in terms of the serving size. The content of phenolics varies among different cultivars, age, generation of the plant, growing conditions, harvest, post-harvest and storage conditions, and the technological procedures used (Toma´s-Barbera´n and Espı´n, 2001). Several studies have reported that boiling vegetables induces the loss of nutrients and bioactive compounds that are unstable to heat. In general, it is considered that cooked vegetables have a lower health-promoting effect than the corresponding raw ones. The rationale for this has traditionally been based on the measurement of selected barely stable antioxidants of nutritional interest (e.g. ascorbic acid) commonly assessed as indicators of the processing damage (Nicoli et al., 1999; Dewanto et al., 2002a,b). Since artichokes are usually cooked before eating, it is important to evaluate the effect of cooking on some nutrients and antioxidant phenolics. There is no report discussing the changes in the contents of various health-promoting phenolics in artichokes that additionally takes into consideration the effects of the stage of maturity of this vegetable. The aim of this study was to obtain data on commonly consumed artichokes, and to compare the chemical composition and
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antioxidant content and activity between mature and immature edible heads. In addition, the effect of cooking on the chemical composition of mature and BA is also described, especially because the data on changes of these compounds during this processing are still limited and sometimes contradictory. 2. Materials and methods 2.1. Materials Artichokes (cv. Green Globe) were grown under typical conditions of soil, irrigation, and illumination in Melipilla, 60 km Southwest from Santiago, Chile. Fifty artichokes, mature and in an early stage of maturity (BA), with an approximate diameter of 11 cm (mature) and 4.5 cm (baby) were manually and randomly picked across the field in December (Summer) of 2008. They were placed in polyethylene bags and transported at 4 8C to the laboratory. Samples were then selected to eliminate damaged and poor quality units and to obtain uniformity. The samples were stored in a refrigerated chamber at 4 8C until extraction and analysis. Sample preparation: Mature sample stems were cut 2 cm below the base of the bud, and BA stems were removed 1 cm below the base of the bud. Mature and BA heads were manually sorted and randomly separated according to their size into two groups, one to be cooked in boiling water (n = 6) and the other to be kept raw (n = 6). Artichoke heads were cooked in boiling water under pressure in a covered pressure 4 L capacity pot for 10 min. Samples were immediately cooled in cold water and drained. Both cooked and raw samples were dried in an oven at 50 8C for 5 days (Asami et al., 2003), ground, sealed in polypropylene bags, and stored at 4 8C until analysis. All measurements were performed by triplicate. 2.2. Chemicals All reagents and solvents were analytical grade chemicals from Merck (Darmstadt, Germany) or Sigma Chemical Co. (St. Louis, MO, USA). 2.3. Proximate analysis Protein content was determined by Kjeldahl (AOAC 920.54) using a factor of 6.25. Crude fat was assessed using the AOAC method 920.39, moisture was assessed using the AOAC method 945.15, and ash was determined using the AOAC method 942.05 (AOAC, 2006). Dietary fiber was measured as described by Lee et al. (1992) and total carbohydrates were estimated by difference (meaning 100 the sum of moisture, protein, fat and ash). 2.4. Preparation of extracts Aqueous (AE) and hydroalcoholic (HE) (ethanol:water 1:1) extracts of mature and BA (raw and boiled) were prepared. To obtain the AE, 5.5 g of each powdered plant material were macerated for 15 min in 30 mL water at room temperature, and 30 mL boiling water were added and kept under continuous stirring for 5 min at 50–70 8C. After cooling at room temperature, the extracts were filtered through glass wool and paper (5A and 131) and taken to a final volume of 100 mL with water. The HE was prepared weighing 5.5 g of each powdered sample, and 60 mL ethanol:water (1:1) was added. The mixture was heated under reflux at 100 8C for 5 min. After cooling at room temperature, the extracts were filtered through glass wool and paper (5A and 131) and taken to a final volume of 100 mL with ethanol:water (1:1). Both extracts were stored in amber vials at 4 8C until analysis.
2.5. Total phenolics (TP) A quantity of 1 mL of each extract was taken to a final volume of 10 mL with water (AE) or ethanol:water (1:1) (HE) and measured by the non-specific colorimetric reaction with the Folin Ciocalteu reagent that measures the reducing capacity of the samples (Singleton and Rossi, 1965) in a spectrophotometer (Perkin Elmer Lambda EZ 201, Norwalk, CT, USA). The measurement was compared to a standard curve prepared with tannic acid in the range 2.5–15 mg tannic acid/100 mL. TP content was expressed as mg of tannic acid equivalents (TAE) per 100 g dry sample. 2.6. Antioxidant activity by free radical scavenging of DPPH Then 50 mL of each extract, previously filtered (0.22 mm), were added 2 mL DPPH (diphenylpicrylhydrazyl) 6 10 5 M in methanol (Molyneaux, 2004). Both AE and HE were measured spectrophotometrically (Perkin Elmer Lambda EZ 201, Norwalk, CT, USA). Absorbance was measured at 517 nm during 16 min using methanol as blank. The antioxidant capacity was expressed as a percentage of inhibition of DPPH radical (% inhibition of DPPH radical) calculated according to the following equation: % inhibition of DPPH radical = [(AC(0) AA(t))/AC(0)] 100, where AC(0): absorbance of the control at time = 0 min; and AA(t): absorbance of the antioxidant at time = 16 min. 2.7. Caffeic acid, chlorogenic acid, and cynarin The HE of raw and boiled artichokes (mature and BA) were centrifuged at 1800 g for 15 min at 20 8C and concentrated with methanol:water (1:1) in a rotary evaporator under reduced pressure at 65 8C. After concentration and filtration (0.22 mm) the polyphenols were measured using a Merck-Hitachi Lachrom HPLC (Merck–Hitachi, Frankfurt–Tokyo, Germany–Japan) equipped with a quaternary pump programmable for gradients, thermostatic controlled column chamber, rheodyne injection valve with a 100 mL sample loop, and UV–visible detector at 326 nm. The column employed was C-18 Lichrospher column (250 mm 4.0 mm, 5 mm), fitted with suitable guard column. The mobile phase was a mixture of (A): H2O adjusted to pH 2.4 with 99% CH3COOH, and (B): CH3CN. The following descendent gradient of solvents was applied: 92% A and 8% B to 30% A and 70% B in 50 min (flow: 0.4 mL/min at 30 8C). Calibration curves were prepared for chlorogenic acid (5–80 mg/L), caffeic acid (0.1– 1.8 mg/L) and cynarin (5–50 mg/L), using the corresponding standards purchased from Sigma Chemical Co. (St. Louis, MO). The analyses were run with six repetitions. 2.8. Statistical analysis The analyses were performed in triplicate; each replicate was quantified in duplicate, unless stated otherwise. All data given represent mean values standard error (SE). Data were processed by two-way analysis of variance (ANOVA) and statistical significance by Student’s t-test. All statistical analysis and correlations were made with SAS1. p < 0.05 was considered significant. We studied the effect of cooking by comparing raw and boiled artichokes and the effect of maturity by comparing the fully grown and BA. 3. Results and discussion 3.1. Effect of cooking on chemical composition The chemical composition of mature and BA (raw and cooked) is reported in Table 1. The moisture content ranged between 76.6 (raw, mature) and 86.2 (BA, cooked) g/100 g f.w., depending on the
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Table 1 Means and standard error of the chemical composition of mature and baby artichokes, raw or cooked (g/100 g) (n = 6). Mature raw Moisture (f.w.) Ash (d.w.) Crude fat (d.w.) Protein (d.w.) Total carbohydrates Dietary fiber (d.w.)
76.60 0.46 7.04 0.05* 1.15 0.15 15.96 0.18 75.85 0.17 65.82 0.30*
Mature cooked *
80.94 0.02 6.70 0.02 1.76 0.13 17.71 0.18 73.84 0.73 63.69 0.46
Baby raw
Baby cooked
81.24 0.08 7.17 0.41 2.36 0.08 12.29 0.10 78.18 0.43* 64.78 0.27*
86.22 0.35* 7.63 0.20 3.47 0.19* 14.45 0.16* 74.45 0.16 59.95 1.33
f.w.: fresh weight; d.w: dry weight. * Values in the same type of parameter and stage of maturity differ significantly (p < 0.05).
maturity and the processing (p < 0.05). As expected, these values increased after cooking, due to water absorption (Pellegrini et al., 2009; Pereira Lima et al., 2009). The ash content of artichokes ranged from 6.7 to 7.6 g/100 g d.w. Ash was higher in BA, but this difference was significant in the cooked samples only (p < 0.05). Mature artichokes exhibited 4.8% less ash content after cooking, while it increased in BA samples by 6.4%. Some minerals probably leached into the cooking water causing a reduction in the ash content. Total lipids varied between 1.15 and 3.47 g/100 g d.w. All samples increased their lipid content after cooking (53% and 47% in mature and BA, respectively), although this difference was significant in BA only (p < 0.05). These changes may be due to a higher extraction of released lipids (Pereira Lima et al., 2009). The total lipid content was significantly higher in the BA (p < 0.05). The crude protein content ranged from 12.3 (raw BA) to 17.7 g/ 100 g d.w. (cooked mature samples). Protein increased by 10.9% in mature and 17.5% in BA after cooking (p < 0.05 in BA only). This is in disagreement with Pereira Lima et al. (2009), who reported a decrease of the protein content in some cooked vegetables. These authors observed different effects of cooking on different vegetables (e.g. in Chinese cabbage cooking induced an increase of sample water content and lipids and a decrease in total protein). The conformation of the vegetable matrix is likely the determinant factor ruling their ability to retain/degrade components affecting the global proximate chemical composition. Carbohydrates ranged from 73.8 to 78.2 mg/100 g d.w. BA contained higher amounts of carbohydrates (p < 0.05), independently of the processing. Total carbohydrates decreased after cooking (by 4.8% in BA and 2.7% in mature artichokes). The loss in BA (p < 0.05) is attributed to the leak of these compounds into the water. The total dietary fiber ranged from 60.0 to 65.8 mg/100 g d.w. In both stages of maturity, cooking decreased the dietary fiber content (by 7.5% in BA and 3.2% in mature samples). The loss may be related with the thermal degradation of polysaccharides, as well as the solubilization of constituents that leak into the water (Svanberg et al., 1997). Cooking may alter the properties of fiber, and changes in total fiber content as well as in extractability have been reported, leading to redistribution between the relative amounts of soluble and insoluble fractions (Puupponen-Pimia¨ et al., 2003).
Table 2 shows that TP in the AE of raw artichokes (mature and BA) contained 5.4 and 4.6 mg TAE/100 g d.w., respectively, while in the HE the values were 5.8 and 5.9 mg TAE/100 g d.w. This indicates that TP in the AE were dependent on the maturity and the thermal processing (p < 0.05). TP in the AE of raw mature samples were 1.2 higher than those contained in BA, while they were similar in the HE, indicating that maturity does not affect these phenolics. Studies performed on different cooked vegetables have reported that TP vary depending on the treatment. They may decrease up to 50% due to antioxidant breakdown and leaking into the water (Gil et al., 1999), may increase due to a higher accessibility (Dewanto et al., 2002a; Puupponen-Pimia¨ et al., 2003; Choi et al., 2006), or may remain unchanged (Oboh, 2005; Sultana et al., 2008; Pellegrini et al., 2009). After cooking, TP content in the AE of mature and BA were 11.9 and 23.4 mg TAE/g d.w., while in the HE the values for mature and BA were 8.1 and 17.4 mg TAE/g d.w., respectively. TP were higher in the extracts obtained from the cooked samples (mature and BA), mainly in the aqueous form, probably due to the high amount of hydrosoluble phenolics, as flavonoids (Wang et al., 2003). The increase after cooking (over 50%) in the AE may also reflect the release of derivatives by hydrolysis. In addition, the increase was higher in BA (between 5.1- and 2.9-fold in the AE and HE, respectively), proving that the thermal processing enhances their potentially healthy value. Additionally, this result may also be at least partially explained by the lack of selectivity of the Folin Ciocalteu method used to measure TP, thus generating overestimated values (Prior et al., 2005; Huang et al., 2005). In agreement with our results, other authors have reported higher TP in artichokes and by-products after water blanching (Llorach et al., 2002; Schu¨tz et al., 2004). The increase may be partly due to a release of bound phenolic acids and the breakdown or softening of cellular constituents of plant cells, leading to augmented accessibility of the antioxidants. These complex compounds may be more easily released in relation to those found in the raw plants, improving their antioxidant capacity. In addition, cooking may cause the breakage of complex structures liberating individual phenolics and/or phenolic degradation products which could also react with the Folin-Ciocalteu reagent (Dewanto et al., 2002a,b; Turkmen et al., 2005; Choi et al., 2006; Sultana et al., 2008). As heating deactivates oxidative enzymes, it also prevents the enzymatic oxidation that causes the loss of
3.2. Effect of cooking on phenolics Cooking vegetables in boiling water is traditionally associated with a reduction of nutritional properties and loss of antioxidants due to oxidation, thermal degradation, leaching and other events that reduce these compounds (Amin and Lee, 2005; Gawlik-Dziki, 2008; Pellegrini et al., 2009). Since it is currently accepted that phenolics are the major contributors to the antioxidant activity of plant foods, it is important to evaluate not only the impact of the stage of maturity, but also the effect of the heat treatment on the TP in artichoke extracts.
Table 2 Means and standard error of the total phenolics concentration of extracts obtained from raw or cooked mature and baby artichokes (mg tannic acid equivalents/100 g sample) (n = 6). Extract
Mature raw
Mature cooked
Baby raw
Baby cooked
AE HE
5.40 0.13 5.76 0.09
11.93 0.30* 8.12 0.05*
4.55 0.14 5.93 0.15
23.38 0.57* 17.40 0.30*
AE: aqueous extract; HE: hydroalcoholic extract. * Values in the same type of extract and stage of maturity differ significantly (p < 0.05).
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Table 3 Means and standard error of the antioxidant capacity of extracts obtained from raw or cooked mature and baby artichokes (% inhibition of DPPH radical) (n = 6). Extract
Mature raw
Mature cooked
Baby raw
Baby cooked
AE HE
30.50 0.14 28.46 0.33
29.60 1.28 34.56 0.63*
5.02 0.17 22.97 0.39
61.26 0.09* 69.91 0.01*
AE: aqueous extract; HE: hydroalcoholic extract. * Values in the same type of extract and stage of maturity differ significantly (p < 0.05).
antioxidants in raw materials. Artichokes are a good source of polyphenol oxidases (PPO) that catalyze the oxidation of phenolics to quinones that subsequently induce the formation of secondary products (Espı´n et al., 1997). PPO may reduce TP in raw artichokes, and since heating inactivates PPO, it enables their preservation. Similar results have been reported in other vegetables (Talcott et al., 2000; Dewanto et al., 2002a,b; Oboh, 2005; Turkmen et al., 2005; Choi et al., 2006; Sultana et al., 2008; Pereira Lima et al., 2009). However, other researchers have reported that cooking reduces TP (Gil et al., 1999; Puupponen-Pimia¨ et al., 2003; Zhang and Hamauzu, 2004; Turkmen et al., 2005; Gliszczyn´ska-S´wiglo et al., 2006; Sultana et al., 2008; Volden et al., 2009). Clearly, the TP content may vary widely due to agricultural factors and processing (Oboh, 2005). The results are also affected by the analytical methodologies and the variety of the phenolics, ranging from simple to very complex molecules. 3.3. Effect of cooking on antioxidant capacity Table 3 shows the capacity of the aqueous and hydroalcoholic extracts to inhibit the DPPH radical at 16 min. The antioxidant capacities of the AE in raw mature and BA were 30.5 and 5.0% inhibition of DPPH radical, respectively, while in the HE the values were 28.5 and 23.0% inhibition of DPPH radical. Thus, the property was dependent both on the maturity and the processing (p < 0.05). Cooking affected the antioxidant capacity of the AE obtained from mature artichokes to a lesser extent, since no differences were observed between raw and cooked samples. The extracts obtained from BA exhibited higher values after thermal treatment (p < 0.05). Cooking increased the antioxidant capacities of the extracts, by 12.2-fold in AE and 3.0-fold in HE, respectively, probably due to a less efficient extractive process in the more rigid mature specimens. On the contrary, in BA there was a more exhaustive extraction of antioxidants, due to the matrix softening and disruption that allowed their release (Pellegrini et al., 2009). The higher antioxidant activity observed in the HE may be partly attributed to the thermal process in alcohol as well, since it improves the efficacy of the extractive process (Mulinacci et al., 2004). This is in agreement with several reports on artichokes and by-products (Llorach et al., 2002; Mulinacci et al., 2004; Jime´nezMonreal et al., 2009; Pellegrini et al., 2009) and other vegetables (Dewanto et al., 2002a,b; Turkmen et al., 2005; Choi et al., 2006; Miglio et al., 2008; Sultana et al., 2008). Many reports indicate that the antioxidant capacity of raw vegetables is higher (Puupponen-Pimia¨ et al., 2003; Wang et al., 2003; Zhang and Hamauzu, 2004; Mulinacci et al., 2004; Gawlik-
Dziki, 2008; Sultana et al., 2008; Volden et al., 2009; Faller and Fialho, 2009), while the antioxidant activity of some vegetables such as squash, peas and leek after cooking remained unchanged (Turkmen et al., 2005). These differences may be explained by the variety of vegetable species and processing methods used. We observed that cooking artichokes in boiling water increased their antioxidant content and activity. In agreement with our data, Ferracane et al. (2008) observed an increase of the total antioxidant capacity values in cooked samples with respect to raw artichokes, independently of the assay used, stating that the spatial arrangement of the phenolic groups can deeply affect the antioxidant activity of the molecules. Different mechanisms have been described to explain similar findings (Volden et al., 2009; Jime´nez-Monreal et al., 2009). In spite of the shortcomings of the Folin Ciocalteu method and the interpretation of the results as TP (Prior et al., 2005; Huang et al., 2005), our study clearly demonstrates that, mainly in immature samples, home cooking can ameliorate the TP content, suggesting that the real intake of these phytochemicals can be underestimated when using data from raw artichokes (Faller and Fialho, 2009). Literature reports on the relationship between TP and the antioxidant capacity are contradictory, and only few high correlations have been observed (Llorach et al., 2002; Wang et al., 2003). The correlation coefficients between TP content and antioxidant capacity of artichokes (BA and mature) demonstrate a strong, positive correlation between these two parameters (p < 0.05). In addition, other non-phenolic compounds, such as antioxidant nutrients, may contribute to the antioxidant capacity of the samples. 3.4. Effect of cooking on polyphenols profile Table 4 shows the caffeic acid, chlorogenic acid and cynarin contents in the extracts obtained from mature and BA (raw or cooked). The phenolics analyzed were dependent on the degree of maturity and processing of the samples. Chlorogenic acid was the predominant phenolic species, followed by cynarin and caffeic acid. Cooking increased the content of caffeic acid 3.6- and 1.8-fold in BA and mature artichokes, respectively (p < 0.05). In addition, cooked BA exhibited the highest caffeic acid content (p < 0.05). Caffeic acid may be considered as a common representative of simple phenolics in vegetables. Caffeic acid content would be the result of monocaffeoylquinic and dicaffeoylquinic acids during processing, so although it may not be detected in fresh samples it may reach measurable amounts in by-products such as juice or pomace (Schu¨tz et al., 2004). Cynarin was at the range of 116.7– 238.2 mg/100 g d.w. It is noteworthy that in raw state mature artichokes contained more cynarin than BA. However, cooking duplicated the amount of cynarin in BA while it decreased by 1.1fold in mature samples. These results may be attributed to the isomerization of dicaffeoylquinic acid during the thermal treatment (Adzet and Puigmacia, 1985) and the esterification of caffeic acid, increasing the cynarin content. These molecular changes and the formation of new compounds are responsible for the increase of the antioxidant capacity observed in cooked artichokes (Kweon et al., 2001). The chlorogenic acid content was at the range of 112.7–456.3 mg/100 g d.w., revealing that it depends both on
Table 4 Means and standard error of the caffeic acid, chlorogenic acid and cynarin content in hydroalcoholic extracts obtained from raw or cooked mature and baby artichokes (mg/ 100 g) (n = 6). Phenol
Mature raw
Mature cooked
Baby raw
Baby cooked
Caffeic acid Cynarin Chlorogenic acid
0.82 0.04 183.46 3.09 184.93 3.77
1.45 0.07* 160.69 3.45* 210.68 2.82*
0.71 0.03 116.72 2.82 112.73 3.23
2.60 0.10* 238.21 6.39* 456.30 14.03*
*
Values in the same type of phenolic compound and stage of maturity differ significantly (p < 0.05).
M. Lutz et al. / Journal of Food Composition and Analysis 24 (2011) 49–54
maturity and thermal processing (p < 0.05). Cooking increased chlorogenic acid by 1.1- and 4.0-fold in mature and BA, respectively. Mulinacci et al. (2004) attributed similar findings to isomerization and hydrolysis events, leading to a substantial redistribution of phenolic acids due to transesterification. In addition, Azzini et al. (2007) observed that chlorogenic acid, monocaffeoylquinic acids, cynarin and dicaffeoylquinic acids increased in mature heads after cooking. Ferracane et al. (2008) observed a significant increase of total caffeoylquinic acids, due to both isomerization and hydrolysis, highlighting the effect of transesterification. This is in agreement with our study, since we observed a steep increase of chlorogenic acid in cooked BA, confirming the increased extractability of these compounds in immature tissues in addition to the chemical changes previously described. We believe that immature tissues are softer, enabling the extractive processes to be more exhaustive. Therefore, the phenolics in BA extracts contributed to the significantly higher TP values, as shown in Table 2. This is also associated to a superior antioxidant capacity (Table 3). Furthermore, this is reinforced by the finding of increased comparative amounts of the three phenolics measured before and after thermal processing. It is difficult to attribute these results to one reason above others, but it is likely to be a combination of facts, among which chemical changes such as isomerization and hydrolysis are determinant.
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