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Antioxidant activities of some dried fruits consumed in Algeria
LWT - Food Science and Technology 49 (2012) 329e332
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Antioxidant activities of some dried fruits consumed in Algeria Salim Ouchemoukh a, *, Said Hachoud a, Hamou Boudraham a, Abderrahmane Mokrani b, Hayette Louaileche b, * a
Laboratoire de Biochimie appliquée, Département de Biologie Physico-Chimique, Faculté des Sciences de la Nature et de la Vie, Université Abderrahmane Mira de Béjaia, Béjaia, Algeria b Laboratoire de Biochimie appliquée, Département des Sciences Alimentaires, Faculté des Sciences de la Nature et de la Vie, Université Abderrahmane Mira de Béjaia, Béjaia, Algeria
a r t i c l e i n f o
a b s t r a c t
Article history: Received 12 June 2011 Received in revised form 12 July 2012 Accepted 15 July 2012
Dried fruits such as prune, apricots, raisins and figs are an important source of different antioxidants which can inhibit the harmful effects of the free radicals. They receive increasing attention for their potential role in prevention of human diseases. The aims of our study were the quantification of some antioxidants (carotenoïds, total phenolic compounds, anthocyanins, flavonoïds and proanthocyanidins) using colorimetric assays and the determination of antioxidant activities by three methods. Three aqueous solvents (distilled water, ethanol and methanol) were used for the extraction of some antioxidants. Apricots and figs had the highest concentration of carotenoïds (10.7 and 10.8 mg bCE/100 g, respectively). Raisins were the richest fruits in total phenolic concentration (1.18 g GAE/100 g) and proanthocyanidins (17.53 mg CE/100 g). Also, figs had the highest concentration of flavonoïds (105.6 mg QE/100 g) and anthocyanins (5.9 mg/100 g). Apricots and raisins possessed a good reducing power, while Agen prune showed significant antioxidant activity to the phosphomolybdate. There were significant correlations between total phenolic concentration and antiradical activity (r ¼ 0.89; p < 0.001) of ethanolic extract and reducing power (r ¼ 0.80; p < 0.01) of aqueous extract. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Vegetables Bioactive compounds Free radicals & chronic diseases
1. Introduction In recent times, natural antioxidants have attracted considerable interest among nutritionists, food manufacturers and consumers because of their presumed safety and potential therapeutic value (Vijaya Kumar Reddy, Sreeramulu, & Raghunath, 2010). Fruits and vegetables are important dietary sources of antioxidant polyphenols for humans. Fruits and vegetables consumption have been shown by multiple epidemiology studies to reduce the risk of chronic diseases such as cancer and heart disease (Vinson, Zubik, Bose, Samman, & Proch, 2005). Fruits are particularly interesting because they are rich in antioxidants and can be consumed on various occasions and as fresh, dried, juice and other processed fruits (Patthamakanokporn, Puwastien, Nitithamyong, Prapaisri, & Sirichakwal, 2008). Antioxidant activity and in particular polyphenol contents of dried fruits are expected to be high due to their low moisture content with increased shelf life (Mariod, Ibrahim, Ismail, & Ismail, 2010). Dried
* Corresponding authors. Tel./fax: þ213 34 21 47 62. E-mail addresses: [email protected] [email protected] (H. Louaileche).
(S.
Ouchemoukh),
0023-6438/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.lwt.2012.07.022
fruits have been studied by many researchers (Breska et al., 2010; Coimbra, Nunes, Cunha, & Guiné, 2011; Ferreira et al., 2002; Marelli et al., 2012; Rivero-Cruz, Zhu, Kinghorn, & Wu, 2008). The drying of fruits is a very ancient practice for food preservation still in use nowadays. The fig is a delicious, nutritive fruit and has medicinal properties that may reduce the risk of cancer and heart disease. Fresh and dried figs are especially rich in antioxidant polyphenols, fiber, trace minerals, proteins, sugars and organic acids. Eight phenols (chlorogenic acid, catechin, epicatechin, rutin, cyanidin-3-O-rutinoside, luteolin-8-C-glucoside, quercetin-3-Oglucoside, kaempferol-3-O-glucoside) were identified in fresh and dried fruits and the predominant phenolic compound was epicatechin (Slatnar, Klancar, Stampar, & Veberic, 2011). Raisins are among solid fruits products having the highest concentration of total phenolic compounds and the highest level of total antioxidant activity. In raisins, the most abundant phenolic compounds are usually quercetin, kaempferol and coumaric acid (Williamson & Carughi, 2010). Meng et al. (2011) reported the presence of 10 phenols (gallic, 3,4 dihydroxybenzoic, caffeic, syringic, ferulic, salicylic and coumaric acids, catechin, quercetin and rutin) in Chinese raisins. 3,4-dihydroxybenzoic acid was the most predominant phenolic compound in these raisins. In this paper, we report antioxidant concentrations and antioxidant activities of some dried fruits commonly consumed in Algeria.
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2. Material and methods 2.1. Chemicals and reagents DPPH (2, 20 -diphenyl-1-picrylhydrazyl), quercetin, b-carotene, FolineCiocalteu’s reagent and hexane was obtained from SigmaeAldrich (Germany), Alfa Aesar (Germany), Fluka (USA), Prolabo (USA) and Riedel-de-Haën (Germany), respectively. All other reagents and chemicals were procured from Biochem Chemopharma (United kingdom). 2.2. Samples Some dried fruits, bought in Bejaia (Algeria) market, were used in the present study: apricots (Prunus armeniaca), white raisins (Vitis vinifera), black figs (Ficus carica) and prune (Prunus domestica). F. carica belongs to Moraceae family and other species to Rosaceae family. Two different prunes were used: prune and Agen prune (region of France). The weight of each sample was approximately 500 g. The fruits were cleaned and edible portions were cut into small pieces before extraction. 2.3. Quantification of antioxidants 2.3.1. Carotenoïds Carotenoïds are pigments insoluble in water and soluble in apolar solvents like hexane. The carotenoids were extracted according to the method of Sass-Kiss, Kiss, Milotay, Kerek, and Toth-Markus (2005). A quantity of crushed fruit (0.2 g for apricots and figs: 1 g for prune and raisins) was added to 10 ml of solvent mixture (hexane, acetone and ethanol, 1:2:1, v/v/v). After 40 min of stirring, the absorbance of upper phase was determined at 450 nm by UVeVIS spectrophotometer (Shimadzu). b-carotene was used as the standard and the results were expressed as mg bcarotene equivalent per 100 g dry weight of fruit (bCE/100 g DW) using the following equation calibration curve: y ¼ 287.63x; R2 ¼ 0.994, where x was the absorbance and y was the b-carotene equivalent. 2.3.2. Anthocyanins Anthocyanin concentration was determined according to the procedure described by Mélo, Lima, Maciel, Caetano, and Leal (2006). One gram of crushed fruit was mixed with 10 ml of ethanolic solution (ethanol/HCl 1.5 mol/l; 85:15, v/v) and allowed to stand in the dark at 4 C overnight. After filtration, the absorbance was measured at 530 nm. The concentrations of anthocyanins were obtained by using a molar extinction coefficient: ε ¼ 38,000 L*mol1 cm1 (Ganjewala, Boba, & Raghavendra, 2008). 2.3.3. Phenolic compounds 2.3.3.1. Preparation of the extracts. Three aqueous solvents (distilled water, ethanol 50 ml/100 ml and methanol 50 ml/100 ml) were used in order to extract the phenolic compounds. Each sample (2 g) was mixed with 20 ml of solvent. After stirring for 40 min, the mixture was centrifuged at 1800 g during 30 min and it was filtered with filter paper.
2.3.3.3. Flavonoïds. The method of Djeridane et al. (2006) was used to determine the concentration of flavonoïds. One milliliter of the extract was mixed with 1 ml of aqueous aluminum chloride (2 g/100 ml). After incubation at room temperature for 10 min, the absorbance of the mixture was read at 410 nm. Total flavonoïd concentration was expressed as mg of quercetin equivalent (QE)/100 g DW (y ¼ 13.03x; R2 ¼ 0.9984). 2.3.3.4. Proanthocyanidins. The concentration of proanthocyanidins was determined by butanoleHCl assay (Maksimovic, Malencic, & Kovacevic, 2005). Extract from dried fruits (0.5 ml) was mixed with 3 ml of butanoleHCl (95:5; v/v) and 0.1 ml of iron sulfate (2 g/ 100 ml). The mixture was incubated at 90 C for 1 h. The absorbance was determined at 530 nm. The results were expressed as mg cyaniding equivalent (CE)/100 g using a molar extinction coefficient of cyanidin: ε ¼ 34,700 L*mol1cm1.
2.4. Antioxidant activities 2.4.1. Antiradical activity The ability of the extracts to scavenge DPPH radical was determined according to the method of Al et al. (2009). Methanolic DPPH solution (100 ml, 6*105 mol/l) was added to 1000 ml of extract. After 20 min of incubation at room temperature, the absorbance was read at 517 nm. The percentage of reduction of radical DPPH was calculated as follows: Radical-scavenging activity % ¼ [(Abscontrol Abssample)/ (Abscontrol)]*100, where Abscontrol is the absorbance of DPPH radical þ methanol and Abssample is the absorbance of DPPH radical þ sample extract. 2.4.2. Reducing power The reducing power of the dried fruits tested was estimated according to the method described by Yildrim, Oktay, and Bilaloglu (2001). One milliliter of the extract was added to 2.5 ml of phosphate buffer (0.2 mol/l, pH 6.6) and 2.5 ml of aqueous potassium ferricyanide solution (1 g/100 ml). After stirring, the mixture was incubated at 50 C for 20 min. Then, 2.5 ml of aqueous trichloroacetic acid solution (10 g/100 ml) were added. 1.25 ml of distilled water and 0.25 ml of aqueous ferric chloride solution (0.1 g/100 ml) were added to 1.25 ml of the mixture. After 10 min, the absorbance was determined at 700 nm. The results were expressed as mg ascorbic acid equivalent (AAE)/100 g DW (y ¼ 11.411x; R2 ¼ 0.9926). 2.4.3. Phosphomolybdenum method The total antioxidant capacities of the extracts were evaluated by the phosphomolybdenum method as described by Ramalakshim, Rahath, and Jagan (2008). One milliliter of the phosphomolybdenum solution (sulfuric acid 0.6 mol/l, sodium phosphate 0.028 mol/l and ammonium molybdate 0.004 mol/l) was added to 100 ml of the extract. After incubation at 90 C for 60 min, the absorbance was determined at 695 nm. The results were expressed as mg AAE/100 g DW (y ¼ 4.8057x; R2 ¼ 0.9938).
2.5. Statistical analysis 2.3.3.2. Total phenolic compounds. The total phenolic compounds concentration of the samples was measured according to the method of Nencini et al. (2007). Extract from dried fruits (200 ml) was mixed with 1 ml of FolineCiocalteu’s reagent. After 3 min, the mixture was neutralized with 800 ml of aqueous sodium carbonate (2 g/100 ml). The blue absorbance was read at 720 nm. The concentration of total phenolics was expressed as mg of gallic acid equivalent (GAE)/100 g DW (y ¼ 4.2753x; R2 ¼ 0.9947).
The averages and the standard deviations are calculated with Microsoft Office Excel 2007. The software STATISTICA 5.5 was used to compare the different results by the analysis of variance with one factor (ANOVA). The results were classified by decreasing order a > b > c > d > e. The values obtained carrying the same letter do not present any significant difference at p < 0.05.
S. Ouchemoukh et al. / LWT - Food Science and Technology 49 (2012) 329e332
3. Results and discussion
Table 2 Concentrations of antioxidants of some dried fruits.
3.1. Antioxidant concentrations
Fruits
The solvents used were mixed with water because polyphenols are polar compounds. The concentrations of carotenoïds and anthocyanins are presented in Table 1; total phenolic compounds, flavonoïds and proanthocyanidins concentrations are given in Table 2. Antioxidant concentrations of dried fruits presented differences. The concentration of carotenoïds of figs and apricots were the highest. The lowest concentrations were recorded in Agen prune, prune and raisins. The statistical analysis revealed no significant difference (p < 0.05) between apricots and figs and between the Agen prune, prune and the raisins. The concentrations of anthocyanins in analyzed fruits presented significant differences (p < 0.05). The figs and the Agen prune possessed high concentrations of these substances. Nevertheless, the lowest concentrations were recorded for the samples of prune, raisins and apricots. These results were in agreement with those reported by Vallejo, marin, and Tomas-Barberan (2012). They obtained high anthocyanin concentrations mainly cyanidin-3-rutinoside (16.9e108.9 mg/ 100 g) in figs. Ethanolic extract of raisins had the highest concentration of total phenolics and aqueous extract of figs was not rich in these compounds. The statistical analysis revealed significant differences between the fruits (p < 0.05), except for the aqueous extracts of apricots and the raisins, methanolic extracts of Agen prune and prune as well as ethanolic apricots and fig extracts. Our result for the concentration of total phenolic compounds of methanolic extract of raisins was superior to those reported by Mishra, Dubey, Mishra, and Barik (2010) (0.83 g/100 g). The highest concentrations of flavonoïds were those of the ethanolic and aqueous extracts of figs. The aqueous extract of raisins presented the lowest concentration. Significant differences were noted between the analyzed samples (p < 0.05). Higher concentrations (107e140 mg/100 g) of flavonoïds for figs were obtained also by Vallejo et al. (2012). The highest concentration of proanthocyanidins was observed in raisins ethanolic extract. For each solvent, apricots presented the lowest concentration of these antioxidants. The concentrations of proanthocyanidins in aqueous, ethanolic and methanolic extracts of raisins were high compared to other fruits. No significant differences were noted Agen prune, prune, apricots and figs (aqueous and ethanolic extracts) as well as for Agen prune and figs (methanolic extracts). The discordance in antioxidant concentrations of fruits between different studies could be due to varietal, seasonal, agronomical differences, genomics, moisture content, method of extraction and standards used (Imeh & Khokhar, 2002). Also, the difference between extracts is due to the varying efficiency of the solvents used.
3.2. Antioxidant activities The results of antioxidant activities are given in Table 3. Aqueous extract of figs had the lowest antiradical activity, whereas ethanolic Table 1 Concentrations of carotenoïds and anthocyanins of some dried fruits. Fruits
Carotenoïds (mg bCE/100 g DW)
Agen prune Prune Apricots Raisins Figs
1.4 1.6 10.7 2.2 11.0
0.4b 0.6b 2.6a 0.2b 1.0a
331
Anthocyanins (mg/100 g DW) 4.0 2.0 0.5 1.0 5.9
1.0b 0.0c 0.0d 0.1cd 0.2a
Values are mean standard deviation (n ¼ 3). Means followed by the same letter are not different according to ANOVA (Analysis Of VAriance).
Total phenolic compounds (g GAE/100 g DW)
Distilled water Agen prune 0.77 Prune 0.73 Apricots 0.65 Raisins 0.65 Figs 0.47 Methanol 50 ml/100 ml Agen prune 0.74 Prune 0.76 Apricots 0.63 Raisins 1.03 Figs 0.52 Ethanol 50 ml/100 ml Agen prune 0.64 Prune 0.74 Apricots 0.54 Raisins 1.18 Figs 0.54
Flavonoïds (mg QE/100 g DW)
Proanthocyanidins (mg CE/100 g DW)
0.02a 0.01ab 0.01b 0.07b 0.00c
59.7 70.1 56.8 20.8 104.5
0.3c 0.6b 0.0d 1.1e 2.1a
3.22 3.15 2.24 7.39 2.18
0.16b 0.01b 0.02b 0.87a 0.08b
0.03b 0.03b 0.00c 0.07a 0.00d
53.0 46.6 31.9 30.9 79.9
0.6b 1.0c 0.8d 0.6e 0.8a
3.3 3.0 2.2 13.2 3.4
0.2b 0.1bc 0.2c 0.1a 0.3b
0.02c 0.00b 0.00d 0.01a 0.00d
42.0 48.7 30.6 28.2 105.6
0.1c 0.7b 0.2d 0.0e 0.5a
3.6 2.7 2.1 17.5 3.2
0.4b 0.0b 0.2b 1.2a 0.0b
Values are mean standard deviation (n ¼ 3). Means followed by the same letter are not different according to ANOVA (Analysis Of VAriance).
extract of raisins had the best DPPH radical scavenging activity. This can be related to the richness in total phenolic compounds of raisins fruit compared to the other fruits. All these fruits showed a capacity to trap radical DPPH and that this property differs significantly (p < 0.05) from a fruit to another, except between Agen prune, prune and raisins (aqueous extracts), prune and raisins (methanolic extracts) and between apricots and figs (ethanolic extract). Reducing power is one of the mechanism of antioxidant activity which measure the conversion of a Fe3þ/ferricyanide complex to the ferrous form. Aqueous extract of apricots and ethanolic extract of raisins showed a highest reducing capacity. On the other hand, aqueous, ethanolic and methanolic extracts of figs showed a weak capacity to reduce iron (III). Agen prune, apricots and raisins (methanolic extract) and Agen prune and apricots (ethanolic extract) did not present a significant difference in their reducing power. Mishra et al. (2010) reported that raisins showed a weak reducing power. However, our results were in discordance with the reported data. Using the phosphomolybdate, aqueous extract of
Table 3 Antioxidant activities of some dried fruits. Fruits
Antiradical activity (%)
Distilled water Agen prune 76.0 7.3a Prune 72.6 6.7ab Apricots 61.2 0.8b Raisins 78.4 0.6a Figs 28.1 3.7c Methanol 50 ml/100 ml Agen prune 80.7 2.4b Prune 87.0 0.6a Apricots 63.3 1.0c Raisins 89.2 1.5a Figs 53.0 0.6d Ethanol 50 ml/100 ml Agen prune 72.3 1.8c Prune 81.7 1.6b Apricots 53.6 0.6d Raisins 92.2 0.4a Figs 55.9 0.7d
Reducing power (mg AAE/100 g DW)
Phosphomolybdenum method (g AAE/100 g DW)
599.9 548.9 680.9 454.5 210.0
3.7b 17.3c 2.1a 3.4d 1.4e
24. 8 5.4 22.0 7.6 22.1
0.9a 0.8b 5.0a 0.4b 0.5a
674.3 623.9 661.2 673.7 232.9
11.8a 0.4b 1.2a 14.1a 6.5c
14.1 21.5 16.4 0.6 14.1
1.2b 0.8a 2.1b 0.1c 0.4b
516.9 569.2 485.9 679.8 221.7
1.0c 10.2b 18.9c 23.5a 0.1d
12.9 21.9 15.4 5.9 17.2
1.0c 1.8a 0.7bc 0.2d 2.3b
Values are mean standard deviation (n ¼ 3). Means followed by the same letter are not different according to ANOVA (Analysis Of VAriance).
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References
Table 4 Correlation matrix between antioxidants and antioxidant activities.
TPC FLA PRO RP AA AAP
TPC
FLA
PRO
RP
AA
AAP
1 0.52 0.84*** 0.68*** 0.80*** 0.41
1 0.44 0.73 0.66 0.39*
1 0.32 0.56** 0.59
1 0.74*** 0.14
1 0.36
1
Abbreviations: TPC, total phenolic compounds; FLA, flavonoïds; PRO, proanthocyanidins; RP, reducing power; AA, antiradical activity; AAP, antioxidant activity with phosphomolybdate. * p < 0.05, **p < 0.01, ***p < 0.001.
Agen prune had the best antioxidant activity. The statistical analysis showed significant differences (p < 0.05) between the fruits, except for the Agen prune, apricots and figs aqueous and methanolic extracts. Differences in cultivation region and practices, ripening stage, harvested conditions and seasons could be the most factors for variation of the antioxidant activity (Patthamakanokporn et al., 2008). Moreover, the antioxidant activity depends on the extraction solvent polarity, the techniques of extraction as well as the process and the temperature of drying. 3.3. Correlations There were statistically significant correlations (Table 4) between antioxidants and antioxidant activities: DPPH radical scavenging activity and total phenolic compounds of ethanolic, methanolic and aqueous extracts, reducing power and total phenolic compounds of aqueous extracts, antiradical activity and proanthocyanidins. Moreover, there was a good correlation between antiradical activity and reducing power of ethanolic extracts. These results were in agreement with those reported by Negi, Jayaprakasha, and Jena (2003), Vijaya Kumar Reddy et al. (2010) & Çaliskan and Polat (2011). The antioxidant activity of phenolic constituents may be related to their redox properties, which allow them to act as reducing agents or hydrogen-atom donors, their ability to chelate metals, inhibit lipoxygenase and scavenge free radicals (Mishra et al., 2010). 4. Conclusion The results obtained showed that the concentrations extracted by the different solvents were quite close and phenolics from raisins were poorly extracted by water. Moreover, lowest concentrations of proanthocyanidins were consistently found in apricot and highest proanthocyanidin concentrations were obtained in raisins, as were total phenolics in the aqueous alcohol extracts. The antioxidant capacity was related to polyphenols content. The figs were the richest fruit in carotenoïds, anthocyanins and flavonoïds. The aqueous extract of apricot presented the best reducing power and Agen prune had the highest antioxidant activity with the phosphomolybdenum method. The raisin extracts showed the highest reduction of DPPH. Apricots, figs, prune and raisins are an excellent dietary source of natural antioxidants and can be considered as foods with remarkable benefits for human health.
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Antioxidant activities of some dried fruits consumed in Algeria Salim Ouchemoukh a, *, Said Hachoud a, Hamou Boudraham a, Abderrahmane Mokrani b, Hayette Louaileche b, * a
Laboratoire de Biochimie appliquée, Département de Biologie Physico-Chimique, Faculté des Sciences de la Nature et de la Vie, Université Abderrahmane Mira de Béjaia, Béjaia, Algeria b Laboratoire de Biochimie appliquée, Département des Sciences Alimentaires, Faculté des Sciences de la Nature et de la Vie, Université Abderrahmane Mira de Béjaia, Béjaia, Algeria
a r t i c l e i n f o
a b s t r a c t
Article history: Received 12 June 2011 Received in revised form 12 July 2012 Accepted 15 July 2012
Dried fruits such as prune, apricots, raisins and figs are an important source of different antioxidants which can inhibit the harmful effects of the free radicals. They receive increasing attention for their potential role in prevention of human diseases. The aims of our study were the quantification of some antioxidants (carotenoïds, total phenolic compounds, anthocyanins, flavonoïds and proanthocyanidins) using colorimetric assays and the determination of antioxidant activities by three methods. Three aqueous solvents (distilled water, ethanol and methanol) were used for the extraction of some antioxidants. Apricots and figs had the highest concentration of carotenoïds (10.7 and 10.8 mg bCE/100 g, respectively). Raisins were the richest fruits in total phenolic concentration (1.18 g GAE/100 g) and proanthocyanidins (17.53 mg CE/100 g). Also, figs had the highest concentration of flavonoïds (105.6 mg QE/100 g) and anthocyanins (5.9 mg/100 g). Apricots and raisins possessed a good reducing power, while Agen prune showed significant antioxidant activity to the phosphomolybdate. There were significant correlations between total phenolic concentration and antiradical activity (r ¼ 0.89; p < 0.001) of ethanolic extract and reducing power (r ¼ 0.80; p < 0.01) of aqueous extract. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Vegetables Bioactive compounds Free radicals & chronic diseases
1. Introduction In recent times, natural antioxidants have attracted considerable interest among nutritionists, food manufacturers and consumers because of their presumed safety and potential therapeutic value (Vijaya Kumar Reddy, Sreeramulu, & Raghunath, 2010). Fruits and vegetables are important dietary sources of antioxidant polyphenols for humans. Fruits and vegetables consumption have been shown by multiple epidemiology studies to reduce the risk of chronic diseases such as cancer and heart disease (Vinson, Zubik, Bose, Samman, & Proch, 2005). Fruits are particularly interesting because they are rich in antioxidants and can be consumed on various occasions and as fresh, dried, juice and other processed fruits (Patthamakanokporn, Puwastien, Nitithamyong, Prapaisri, & Sirichakwal, 2008). Antioxidant activity and in particular polyphenol contents of dried fruits are expected to be high due to their low moisture content with increased shelf life (Mariod, Ibrahim, Ismail, & Ismail, 2010). Dried
* Corresponding authors. Tel./fax: þ213 34 21 47 62. E-mail addresses: [email protected] [email protected] (H. Louaileche).
(S.
Ouchemoukh),
0023-6438/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.lwt.2012.07.022
fruits have been studied by many researchers (Breska et al., 2010; Coimbra, Nunes, Cunha, & Guiné, 2011; Ferreira et al., 2002; Marelli et al., 2012; Rivero-Cruz, Zhu, Kinghorn, & Wu, 2008). The drying of fruits is a very ancient practice for food preservation still in use nowadays. The fig is a delicious, nutritive fruit and has medicinal properties that may reduce the risk of cancer and heart disease. Fresh and dried figs are especially rich in antioxidant polyphenols, fiber, trace minerals, proteins, sugars and organic acids. Eight phenols (chlorogenic acid, catechin, epicatechin, rutin, cyanidin-3-O-rutinoside, luteolin-8-C-glucoside, quercetin-3-Oglucoside, kaempferol-3-O-glucoside) were identified in fresh and dried fruits and the predominant phenolic compound was epicatechin (Slatnar, Klancar, Stampar, & Veberic, 2011). Raisins are among solid fruits products having the highest concentration of total phenolic compounds and the highest level of total antioxidant activity. In raisins, the most abundant phenolic compounds are usually quercetin, kaempferol and coumaric acid (Williamson & Carughi, 2010). Meng et al. (2011) reported the presence of 10 phenols (gallic, 3,4 dihydroxybenzoic, caffeic, syringic, ferulic, salicylic and coumaric acids, catechin, quercetin and rutin) in Chinese raisins. 3,4-dihydroxybenzoic acid was the most predominant phenolic compound in these raisins. In this paper, we report antioxidant concentrations and antioxidant activities of some dried fruits commonly consumed in Algeria.
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2. Material and methods 2.1. Chemicals and reagents DPPH (2, 20 -diphenyl-1-picrylhydrazyl), quercetin, b-carotene, FolineCiocalteu’s reagent and hexane was obtained from SigmaeAldrich (Germany), Alfa Aesar (Germany), Fluka (USA), Prolabo (USA) and Riedel-de-Haën (Germany), respectively. All other reagents and chemicals were procured from Biochem Chemopharma (United kingdom). 2.2. Samples Some dried fruits, bought in Bejaia (Algeria) market, were used in the present study: apricots (Prunus armeniaca), white raisins (Vitis vinifera), black figs (Ficus carica) and prune (Prunus domestica). F. carica belongs to Moraceae family and other species to Rosaceae family. Two different prunes were used: prune and Agen prune (region of France). The weight of each sample was approximately 500 g. The fruits were cleaned and edible portions were cut into small pieces before extraction. 2.3. Quantification of antioxidants 2.3.1. Carotenoïds Carotenoïds are pigments insoluble in water and soluble in apolar solvents like hexane. The carotenoids were extracted according to the method of Sass-Kiss, Kiss, Milotay, Kerek, and Toth-Markus (2005). A quantity of crushed fruit (0.2 g for apricots and figs: 1 g for prune and raisins) was added to 10 ml of solvent mixture (hexane, acetone and ethanol, 1:2:1, v/v/v). After 40 min of stirring, the absorbance of upper phase was determined at 450 nm by UVeVIS spectrophotometer (Shimadzu). b-carotene was used as the standard and the results were expressed as mg bcarotene equivalent per 100 g dry weight of fruit (bCE/100 g DW) using the following equation calibration curve: y ¼ 287.63x; R2 ¼ 0.994, where x was the absorbance and y was the b-carotene equivalent. 2.3.2. Anthocyanins Anthocyanin concentration was determined according to the procedure described by Mélo, Lima, Maciel, Caetano, and Leal (2006). One gram of crushed fruit was mixed with 10 ml of ethanolic solution (ethanol/HCl 1.5 mol/l; 85:15, v/v) and allowed to stand in the dark at 4 C overnight. After filtration, the absorbance was measured at 530 nm. The concentrations of anthocyanins were obtained by using a molar extinction coefficient: ε ¼ 38,000 L*mol1 cm1 (Ganjewala, Boba, & Raghavendra, 2008). 2.3.3. Phenolic compounds 2.3.3.1. Preparation of the extracts. Three aqueous solvents (distilled water, ethanol 50 ml/100 ml and methanol 50 ml/100 ml) were used in order to extract the phenolic compounds. Each sample (2 g) was mixed with 20 ml of solvent. After stirring for 40 min, the mixture was centrifuged at 1800 g during 30 min and it was filtered with filter paper.
2.3.3.3. Flavonoïds. The method of Djeridane et al. (2006) was used to determine the concentration of flavonoïds. One milliliter of the extract was mixed with 1 ml of aqueous aluminum chloride (2 g/100 ml). After incubation at room temperature for 10 min, the absorbance of the mixture was read at 410 nm. Total flavonoïd concentration was expressed as mg of quercetin equivalent (QE)/100 g DW (y ¼ 13.03x; R2 ¼ 0.9984). 2.3.3.4. Proanthocyanidins. The concentration of proanthocyanidins was determined by butanoleHCl assay (Maksimovic, Malencic, & Kovacevic, 2005). Extract from dried fruits (0.5 ml) was mixed with 3 ml of butanoleHCl (95:5; v/v) and 0.1 ml of iron sulfate (2 g/ 100 ml). The mixture was incubated at 90 C for 1 h. The absorbance was determined at 530 nm. The results were expressed as mg cyaniding equivalent (CE)/100 g using a molar extinction coefficient of cyanidin: ε ¼ 34,700 L*mol1cm1.
2.4. Antioxidant activities 2.4.1. Antiradical activity The ability of the extracts to scavenge DPPH radical was determined according to the method of Al et al. (2009). Methanolic DPPH solution (100 ml, 6*105 mol/l) was added to 1000 ml of extract. After 20 min of incubation at room temperature, the absorbance was read at 517 nm. The percentage of reduction of radical DPPH was calculated as follows: Radical-scavenging activity % ¼ [(Abscontrol Abssample)/ (Abscontrol)]*100, where Abscontrol is the absorbance of DPPH radical þ methanol and Abssample is the absorbance of DPPH radical þ sample extract. 2.4.2. Reducing power The reducing power of the dried fruits tested was estimated according to the method described by Yildrim, Oktay, and Bilaloglu (2001). One milliliter of the extract was added to 2.5 ml of phosphate buffer (0.2 mol/l, pH 6.6) and 2.5 ml of aqueous potassium ferricyanide solution (1 g/100 ml). After stirring, the mixture was incubated at 50 C for 20 min. Then, 2.5 ml of aqueous trichloroacetic acid solution (10 g/100 ml) were added. 1.25 ml of distilled water and 0.25 ml of aqueous ferric chloride solution (0.1 g/100 ml) were added to 1.25 ml of the mixture. After 10 min, the absorbance was determined at 700 nm. The results were expressed as mg ascorbic acid equivalent (AAE)/100 g DW (y ¼ 11.411x; R2 ¼ 0.9926). 2.4.3. Phosphomolybdenum method The total antioxidant capacities of the extracts were evaluated by the phosphomolybdenum method as described by Ramalakshim, Rahath, and Jagan (2008). One milliliter of the phosphomolybdenum solution (sulfuric acid 0.6 mol/l, sodium phosphate 0.028 mol/l and ammonium molybdate 0.004 mol/l) was added to 100 ml of the extract. After incubation at 90 C for 60 min, the absorbance was determined at 695 nm. The results were expressed as mg AAE/100 g DW (y ¼ 4.8057x; R2 ¼ 0.9938).
2.5. Statistical analysis 2.3.3.2. Total phenolic compounds. The total phenolic compounds concentration of the samples was measured according to the method of Nencini et al. (2007). Extract from dried fruits (200 ml) was mixed with 1 ml of FolineCiocalteu’s reagent. After 3 min, the mixture was neutralized with 800 ml of aqueous sodium carbonate (2 g/100 ml). The blue absorbance was read at 720 nm. The concentration of total phenolics was expressed as mg of gallic acid equivalent (GAE)/100 g DW (y ¼ 4.2753x; R2 ¼ 0.9947).
The averages and the standard deviations are calculated with Microsoft Office Excel 2007. The software STATISTICA 5.5 was used to compare the different results by the analysis of variance with one factor (ANOVA). The results were classified by decreasing order a > b > c > d > e. The values obtained carrying the same letter do not present any significant difference at p < 0.05.
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3. Results and discussion
Table 2 Concentrations of antioxidants of some dried fruits.
3.1. Antioxidant concentrations
Fruits
The solvents used were mixed with water because polyphenols are polar compounds. The concentrations of carotenoïds and anthocyanins are presented in Table 1; total phenolic compounds, flavonoïds and proanthocyanidins concentrations are given in Table 2. Antioxidant concentrations of dried fruits presented differences. The concentration of carotenoïds of figs and apricots were the highest. The lowest concentrations were recorded in Agen prune, prune and raisins. The statistical analysis revealed no significant difference (p < 0.05) between apricots and figs and between the Agen prune, prune and the raisins. The concentrations of anthocyanins in analyzed fruits presented significant differences (p < 0.05). The figs and the Agen prune possessed high concentrations of these substances. Nevertheless, the lowest concentrations were recorded for the samples of prune, raisins and apricots. These results were in agreement with those reported by Vallejo, marin, and Tomas-Barberan (2012). They obtained high anthocyanin concentrations mainly cyanidin-3-rutinoside (16.9e108.9 mg/ 100 g) in figs. Ethanolic extract of raisins had the highest concentration of total phenolics and aqueous extract of figs was not rich in these compounds. The statistical analysis revealed significant differences between the fruits (p < 0.05), except for the aqueous extracts of apricots and the raisins, methanolic extracts of Agen prune and prune as well as ethanolic apricots and fig extracts. Our result for the concentration of total phenolic compounds of methanolic extract of raisins was superior to those reported by Mishra, Dubey, Mishra, and Barik (2010) (0.83 g/100 g). The highest concentrations of flavonoïds were those of the ethanolic and aqueous extracts of figs. The aqueous extract of raisins presented the lowest concentration. Significant differences were noted between the analyzed samples (p < 0.05). Higher concentrations (107e140 mg/100 g) of flavonoïds for figs were obtained also by Vallejo et al. (2012). The highest concentration of proanthocyanidins was observed in raisins ethanolic extract. For each solvent, apricots presented the lowest concentration of these antioxidants. The concentrations of proanthocyanidins in aqueous, ethanolic and methanolic extracts of raisins were high compared to other fruits. No significant differences were noted Agen prune, prune, apricots and figs (aqueous and ethanolic extracts) as well as for Agen prune and figs (methanolic extracts). The discordance in antioxidant concentrations of fruits between different studies could be due to varietal, seasonal, agronomical differences, genomics, moisture content, method of extraction and standards used (Imeh & Khokhar, 2002). Also, the difference between extracts is due to the varying efficiency of the solvents used.
3.2. Antioxidant activities The results of antioxidant activities are given in Table 3. Aqueous extract of figs had the lowest antiradical activity, whereas ethanolic Table 1 Concentrations of carotenoïds and anthocyanins of some dried fruits. Fruits
Carotenoïds (mg bCE/100 g DW)
Agen prune Prune Apricots Raisins Figs
1.4 1.6 10.7 2.2 11.0
0.4b 0.6b 2.6a 0.2b 1.0a
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Anthocyanins (mg/100 g DW) 4.0 2.0 0.5 1.0 5.9
1.0b 0.0c 0.0d 0.1cd 0.2a
Values are mean standard deviation (n ¼ 3). Means followed by the same letter are not different according to ANOVA (Analysis Of VAriance).
Total phenolic compounds (g GAE/100 g DW)
Distilled water Agen prune 0.77 Prune 0.73 Apricots 0.65 Raisins 0.65 Figs 0.47 Methanol 50 ml/100 ml Agen prune 0.74 Prune 0.76 Apricots 0.63 Raisins 1.03 Figs 0.52 Ethanol 50 ml/100 ml Agen prune 0.64 Prune 0.74 Apricots 0.54 Raisins 1.18 Figs 0.54
Flavonoïds (mg QE/100 g DW)
Proanthocyanidins (mg CE/100 g DW)
0.02a 0.01ab 0.01b 0.07b 0.00c
59.7 70.1 56.8 20.8 104.5
0.3c 0.6b 0.0d 1.1e 2.1a
3.22 3.15 2.24 7.39 2.18
0.16b 0.01b 0.02b 0.87a 0.08b
0.03b 0.03b 0.00c 0.07a 0.00d
53.0 46.6 31.9 30.9 79.9
0.6b 1.0c 0.8d 0.6e 0.8a
3.3 3.0 2.2 13.2 3.4
0.2b 0.1bc 0.2c 0.1a 0.3b
0.02c 0.00b 0.00d 0.01a 0.00d
42.0 48.7 30.6 28.2 105.6
0.1c 0.7b 0.2d 0.0e 0.5a
3.6 2.7 2.1 17.5 3.2
0.4b 0.0b 0.2b 1.2a 0.0b
Values are mean standard deviation (n ¼ 3). Means followed by the same letter are not different according to ANOVA (Analysis Of VAriance).
extract of raisins had the best DPPH radical scavenging activity. This can be related to the richness in total phenolic compounds of raisins fruit compared to the other fruits. All these fruits showed a capacity to trap radical DPPH and that this property differs significantly (p < 0.05) from a fruit to another, except between Agen prune, prune and raisins (aqueous extracts), prune and raisins (methanolic extracts) and between apricots and figs (ethanolic extract). Reducing power is one of the mechanism of antioxidant activity which measure the conversion of a Fe3þ/ferricyanide complex to the ferrous form. Aqueous extract of apricots and ethanolic extract of raisins showed a highest reducing capacity. On the other hand, aqueous, ethanolic and methanolic extracts of figs showed a weak capacity to reduce iron (III). Agen prune, apricots and raisins (methanolic extract) and Agen prune and apricots (ethanolic extract) did not present a significant difference in their reducing power. Mishra et al. (2010) reported that raisins showed a weak reducing power. However, our results were in discordance with the reported data. Using the phosphomolybdate, aqueous extract of
Table 3 Antioxidant activities of some dried fruits. Fruits
Antiradical activity (%)
Distilled water Agen prune 76.0 7.3a Prune 72.6 6.7ab Apricots 61.2 0.8b Raisins 78.4 0.6a Figs 28.1 3.7c Methanol 50 ml/100 ml Agen prune 80.7 2.4b Prune 87.0 0.6a Apricots 63.3 1.0c Raisins 89.2 1.5a Figs 53.0 0.6d Ethanol 50 ml/100 ml Agen prune 72.3 1.8c Prune 81.7 1.6b Apricots 53.6 0.6d Raisins 92.2 0.4a Figs 55.9 0.7d
Reducing power (mg AAE/100 g DW)
Phosphomolybdenum method (g AAE/100 g DW)
599.9 548.9 680.9 454.5 210.0
3.7b 17.3c 2.1a 3.4d 1.4e
24. 8 5.4 22.0 7.6 22.1
0.9a 0.8b 5.0a 0.4b 0.5a
674.3 623.9 661.2 673.7 232.9
11.8a 0.4b 1.2a 14.1a 6.5c
14.1 21.5 16.4 0.6 14.1
1.2b 0.8a 2.1b 0.1c 0.4b
516.9 569.2 485.9 679.8 221.7
1.0c 10.2b 18.9c 23.5a 0.1d
12.9 21.9 15.4 5.9 17.2
1.0c 1.8a 0.7bc 0.2d 2.3b
Values are mean standard deviation (n ¼ 3). Means followed by the same letter are not different according to ANOVA (Analysis Of VAriance).
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References
Table 4 Correlation matrix between antioxidants and antioxidant activities.
TPC FLA PRO RP AA AAP
TPC
FLA
PRO
RP
AA
AAP
1 0.52 0.84*** 0.68*** 0.80*** 0.41
1 0.44 0.73 0.66 0.39*
1 0.32 0.56** 0.59
1 0.74*** 0.14
1 0.36
1
Abbreviations: TPC, total phenolic compounds; FLA, flavonoïds; PRO, proanthocyanidins; RP, reducing power; AA, antiradical activity; AAP, antioxidant activity with phosphomolybdate. * p < 0.05, **p < 0.01, ***p < 0.001.
Agen prune had the best antioxidant activity. The statistical analysis showed significant differences (p < 0.05) between the fruits, except for the Agen prune, apricots and figs aqueous and methanolic extracts. Differences in cultivation region and practices, ripening stage, harvested conditions and seasons could be the most factors for variation of the antioxidant activity (Patthamakanokporn et al., 2008). Moreover, the antioxidant activity depends on the extraction solvent polarity, the techniques of extraction as well as the process and the temperature of drying. 3.3. Correlations There were statistically significant correlations (Table 4) between antioxidants and antioxidant activities: DPPH radical scavenging activity and total phenolic compounds of ethanolic, methanolic and aqueous extracts, reducing power and total phenolic compounds of aqueous extracts, antiradical activity and proanthocyanidins. Moreover, there was a good correlation between antiradical activity and reducing power of ethanolic extracts. These results were in agreement with those reported by Negi, Jayaprakasha, and Jena (2003), Vijaya Kumar Reddy et al. (2010) & Çaliskan and Polat (2011). The antioxidant activity of phenolic constituents may be related to their redox properties, which allow them to act as reducing agents or hydrogen-atom donors, their ability to chelate metals, inhibit lipoxygenase and scavenge free radicals (Mishra et al., 2010). 4. Conclusion The results obtained showed that the concentrations extracted by the different solvents were quite close and phenolics from raisins were poorly extracted by water. Moreover, lowest concentrations of proanthocyanidins were consistently found in apricot and highest proanthocyanidin concentrations were obtained in raisins, as were total phenolics in the aqueous alcohol extracts. The antioxidant capacity was related to polyphenols content. The figs were the richest fruit in carotenoïds, anthocyanins and flavonoïds. The aqueous extract of apricot presented the best reducing power and Agen prune had the highest antioxidant activity with the phosphomolybdenum method. The raisin extracts showed the highest reduction of DPPH. Apricots, figs, prune and raisins are an excellent dietary source of natural antioxidants and can be considered as foods with remarkable benefits for human health.
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