Antioxidant and Free Radical Scavenging Activities of Different Plant Parts from Two Erica Species
Abstract
Aqueous extractions from two species of Erica consumed as infusions in several countries to heal ailments were investigated for their phenolic and flavonoid contents, along with antioxidant capacity and radical scavenging capacity using total antioxidant activity, ferric‐reducing antioxidant power, reducing power, 1,1‐diphenyl‐2‐picrylhydrazyl and 2‐2'‐azino‐bis(3 ethylbenzothiazoline‐6‐sulfonic acid) radicals, respectively. Antioxidant properties and total phenolic content differed significantly among these plants. Aqueous extracts of leaves possessed, on average, the highest antioxidant capacity and phenolic content (34.09 ± 10.81 mg ascorbic acid equivalent/g dry weight and 30.59 ± 10.19 mg gallic acid equivalent/g dry weight, respectively) of all three plant parts. A significant correlation (r2 = 0.952) between antioxidant capacity and total phenolic content was found, indicating that phenolic compounds are the major contributors to the antioxidant properties of these plants. Upon application of hierarchical cluster analysis to the results obtained, leaves with flowers were grouped in one cluster, whereas branches remained in another cluster, showing little interference from the collection site or species factors.
Practical Applications
Results obtained support that there may exist benefits for health from ingesting this plant infusions and that these plants have a great potential to serve as a cheap antioxidant source.
Introduction
Since ancient times, humans have used plants to treat many kinds of illnesses. This knowledge is passed down, from elders to younger people, passing it through generations until our days. In most countries, folk medicine was dropped by allopathic practice (Neves et al. 2009). However, the majority of approved drugs against cancer and infectious diseases are of natural origin, meaning plants contain powerful compounds, capable of preventing or treating some illnesses (Newman et al. 2003; Akkol et al. 2008). Over the time, with increasing pollution of modernized world and changes in lifestyle, some illnesses became more common (Kan et al. 2008; Teixeira et al. 2010). Cancer, atherosclerosis, degenerative diseases such as Alzheimer, as well as precocious aging are caused by free radicals, which can be neutralized by antioxidants, and some of the biggest natural sources are plants and fruits (Bondet et al. 1997). This relative abundance of antioxidants has led to an increasing interest in plants, which translated in numerous research in the Mediterranean region, where Portugal is also included. These investigations are important because not every plant has the same amount and type of antioxidants, making some plants more valuable in potential health benefits. Studies usually focus on analyzing species that exist in their country, and some plants used in folklore medicine, usually served as infusions, are already proved to be beneficial. Some examples are Melissa officinalis and Rosmarinus officinalis (Allahverdiyev et al. 2004; Benincá et al. 2011). Erica genuses are used in the form of infusions especially in Morocco and Turkey's folk medicine as diuretic, antiseptic and to treat infections (Akkol et al. 2008; Luís et al. 2009). In Portugal, it is used to treat prostrate, kidney and bladder problems (Neves et al. 2009). In addition, the wood of Erica has economic value as pipe material. Totally, 10 species are reported in Portugal of which two species were collected for this study, Erica arborea L. and Erica australis L., white and pink flowers, respectively. Some studies on Erica species, especially in E. arborea L., exhibited compounds such as flavonoids, which are polyphenols that have been proven to help prevent heart diseases, anthocyanidins among others (Carvalho et al. 2011). Also, a new phenylpropanoid glucoside, named ericarborin, was identified in this specie (Nazemiyeh et al. 2008). In addition, E. arborea L. extract possessed anti‐inflammatory activity (Akkol et al. 2008). However, most studies have lack of variability, few collection sites, and limited number of plant parts or low diversity of assays performed. Therefore, the present work was aimed at providing a more systematic analysis of these bushes regarding phenolic content and antioxidant capacity of leaves, flowers and branches, to determine the factor (location, species or plant part) that has the biggest influence on the antioxidant capacity and ascertain their potential value as sources of these compounds.
Materials and Methods
Reagents
1,1‐Diphenyl‐2‐picrylhydrazyl (DPPH), Folin–Ciocalteu reagent, 2‐2'‐azino‐bis(3 ethylbenzothiazoline‐6‐sulfonic acid) diammonium salt (ABTS), ammonium molybdate, sodium phosphate dibasic dehydrate, monosodium phosphate hydrous, gallic acid, quercetin and Trolox were purchased from Sigma‐Aldrich Co. Ltd. (Poole, U.K.). Iron (III) chloride, methanol, trichloroacetic acid, sodium acetate, sodium carbonate, sulfuric acid, glacial acetic acid, 2,4,6‐tripyridyl‐2‐triazine (TPTZ), hydrochloric acid and ascorbic acid were purchased from VWR (West Chester, PA). Aluminum chloride and absolute ethanol were purchased from Merck (Nottingham, U.K.). All reagents were of analytical grade.
Equipment
All measurements were made using a UV/Vis spectrometer (T70+ UV/Vis Spectrometer, PG Instruments Ltd., Leicestershire, England).
Methods
Plant Materials
Samples from wild Erica spp. plants were randomly selected and collected during the blooming period at the end at start of summer 2010. Five plant samples were collected, all from the Algarve region (Portugal): location 1 (E. australis L., Ponte do Leitejo, 37.125644, –8.314858), from which leaves (ID 1) and branches (ID 6) were separated; location 2 (E. australis L., Feiteira, 37.426508, –7.921556), from which leaves (ID 2), flowers (ID 4) and branches (ID 7) were separated; location 3 (E. australis L., Cotifo, 37.18757, −8.695348), from which leaves (ID 3), flowers (ID 5) and branches (ID 8) were separated; location 4 (E. arborea L., Barranco do Velho 1, 37.2319, –7.9382), from which leaves (ID 9) and branches (ID 12) were separated; location 5 (E. arborea L., Barranco do Velho 2, 37.1204, –7.9353), from which leaves (ID 10), flowers (ID 11) and branches (ID 12) were separated. Samples from locations 1 and 5 did not have enough flowers to proceed with the extraction, for this reason flowers from these samples were not analyzed. All samples were collected on a sunny day. After collection, plant material was stored in a dry place, completely protected from sunlight. Samples were naturally air dried for about a week. After drying, leaves, flowers and branches were manually separated. Leaves and flowers were stored in plastic vials at −4C while branches were stored at room temperature until extraction.
Plant Extraction
On the day of extraction, leaves were ground on a mortar and pestle at room temperature, while flowers had to be frozen with liquid nitrogen prior to grinding, because of a hard core. Branches were ground by kitchen grinding equipment. Plant materials (2 g) were packed in a cloth bag to reduce migration of powder, and added to 30 mL of distilled water (at initial temperature of 95C) for 15 min, with stirring. Infusions were filtered through Whatman no. 4 paper, and their volume was made up to 25 mL. Aqueous infusions were finally transferred to Eppendorfs and stored at −4C. On the day of analysis, extracts were put on ice, protected from light until unfrozen.
Total Phenolic Content
Total phenolic content (TPC) in infusions was determined according to spectrophotometric procedure (Singleton and Rossi 1965). Briefly, 0.1 mL of properly diluted extract was mixed with 0.5 mL Folin–Ciocalteu's reagent and 0.4 mL of a saturated sodium carbonate solution (7.5%). After standing for 30 min in a dark room, absorbance was read at 765 nm against a blank in a spectrophotometer. TPC was calculated by a calibration curve of gallic acid and the results were expressed as mg GAE/g dw (gallic acid equivalent per gram dry weight used in extraction).
Total Flavonoid Content
Total flavonoid content (TFC) was analyzed using a spectrophotometer (Lamaison and Carnat 1990). Properly diluted extract (0.5 mL) was mixed with 2% methanolic AlCl3·6H2O (1.0 mL). The absorbance was measured at 430 nm after standing for 10 min in a dark room. Flavonoid content was calculated by a calibration curve of quercetin, and the results were expressed as mg QE (quercetin equivalent)/g dw.
Total Antioxidant Activity
Total antioxidant activity (TAA) of extracts was determined using a spectrophotometer (Prieto et al. 1998). Briefly, 0.1 mL of properly diluted extract was mixed with 1.0 mL of reagent solution (0.6 M sulfuric acid, 28 mM sodium phosphate and 4 mM ammonium molybdate). Mixture was then incubated at 95C for 90 min in a water bath. Absorbance was measured at 695 nm and results were calculated from an ascorbic acid calibration curve. Results were expressed as mg AAE (ascorbic acid equivalent)/g dw.
Reducing Power
Reducing power (RP) was determined by the spectrophotometric method previously described by Oyaizu (1986). Briefly, 0.2 mL of properly diluted extract in 0.5 mL of sodium phosphate buffer (0.2 M, pH 6.6) was mixed with 0.5 mL potassium ferricyanide (1%) and mixture was incubated at 50C for 20 min. About 0.5 mL of trichloroacetic acid (10%) was then added and mixture was centrifuged at 650× g for 10 min. About 0.5 mL of supernatant was then mixed with 0.5 mL of distilled water and 0.1 mL of ferric chloride (0.1%). Absorbance was measured at 700 nm. Results were expressed as mg Trolox/g dw.
Ferric‐Reducing Antioxidant Power
Ferric‐reducing antioxidant power (FRAP) was determined by the spectrophotometric method previously described by Benzie and Strain (1996). Three stock solutions were prepared: a 300 mM acetate buffer (3.1 g C2H3NaO2·3H2O and 16 mL C2H4O2 for each liter of solution), pH = 3.6, a 10 mM TPTZ solution in 40 mM HCl, and a 20 mM FeCl3·6H2O solution. Working solution was prepared by mixing 25 mL of acetate buffer, 2.5 mL of TPTZ solution and 2.5 mL of FeCl3·6H2O solution. This working solution was then heated to 37C. A 75 μL aliquot of properly diluted extract was mixed with 1.425 mL of working solution. Absorbance was read at 593 nm 30 min after mixing. Results were calculated from a Trolox calibration curve and expressed as mg Trolox/g dw.
DPPH Radical Scavenging Capacity
DPPH scavenging effect of extracts was determined using DPPH radical scavenging capacity (DPPH) method with slight modifications (Blois 1958). Briefly, 1.0 mL of a 0.16 mM DPPH solution was added to the test tube containing 1.0 mL of properly diluted extract in different concentrations. Mixture was then vortexed for 1 min at 800 rpm and kept in the dark for 30 min at room temperature. Absorbance of samples was measured at 517 nm. The percentage radical scavenging capacity (inhibitory concentration [IC]) was calculated using the following formula: (IC) = ([A0 − At]/A0) × 100, where A0 is absorbance of control at 30 min and At is absorbance of sample at 30 min. Results were expressed as μg sample/mL in the form of IC50, determined by linear regression of IC and extract concentration at 50% inhibition.
ABTS Radical Scavenging Capacity
Extract ABTS radical scavenging capacity (ABTS) was determined using a spectrophotometer (Re et al. 1998). A stock solution of ABTS radical was prepared by reacting ABTS (7 mM in water) solution with potassium persulfate (2.45 mM final concentration) and allowing this mixture to stand in dark at room temperature for 12–16 h before use. Stock solution of ABTS was diluted just before use to an absorbance of 0.70 (+0.02) at 734 nm. About 2 mL of diluted ABTS was added to 100 μL of properly diluted extract, and mixed thoroughly. Absorbance was read 5 min after mixing. Results were expressed as μg sample/mL in the form of IC50.
Statistical Analysis
Statistical analysis was performed using SPSS 18.0 (SPSS Inc, Chigaco, IL). The α level was fixed at 0.05. All results are shown as mean ± standard deviation from three repetitions, carried on the same day by taking separate aliquots from the same sample flask. Data were treated for multiple comparisons by analysis of variance in order to verify if species, plant part or location explained results to variability. When homogeneity of variance was not verified by Levene's test, Welch statistics was used instead. Fisher's least significant difference or Games–Howell post hoc tests were performed to determine statistically significant means. Finally, samples or assays were divided into similar groups through a hierarchical cluster analysis (HCA) using between‐group linkage and squared Euclidian distance.
Results and Discussion
Total Phenolic and Flavonoid Contents
Phenolic compounds are commonly found in both edible and nonedible plants, and they have been reported to have multiple biological effects, including antioxidant activity. Flavonoids constitute a special class of polyphenols, with over 4,000 identified species (Carvalho et al. 2011). These compounds are mainly present as coloring pigments in plants but also function as potent antioxidants at various levels, with their antioxidant activity depending mainly on the number and positions of hydroxyl groups and other substituents, and glycosylation. Results are shown in Table 1, and are organized by species and plant part. In general, both TPC and TFC results differ significantly (P < 0.05) for species, plant part and location, but these factors have more influence on the TPCs than they have on the flavonoid contents. In both assays, E. australis L. performed generally better than E. arborea L., but plant part presented the same order for both methods, leaves > flowers > branches, with average results of 30.6; 24.4; 7.8 (mg GAE/g dw) and 4.0; 0.5; 0.21 (mg QE/g dw), respectively. These results are different from other previously published data for the same genus. Luís et al. (2009) and Ay et al. (2007) reported higher values of TPC and TFC than those obtained in the current study. These differences can be explained by several factors such as collection site, extraction procedures and quantification methodologies used. However, results were higher than the average of most plants. From a study of 102 Chinese medicinal plants performed by Cai et al. (2004), only 17 showed higher values than the highest Erica value, and from 133 Indian medicinal plant extracts only 19 were higher than the highest value obtained (Surveswaran et al. 2007), which puts the plant studied in a good position compared to many medicinal plants. Regarding flavonoids, the results are on par with other plants, such as M. officinalis, Salvia officinalis and Mentha piperita analyzed by Atanassova et al. (2011) or Hibiscus stems and leaves analyzed by Patel et al. (2010).
| Species | Plant part | Location | Sample ID | TPC (mg GAE/g dw) | TFC (mg QE/g dw) |
|---|---|---|---|---|---|
| Erica australis | Leaves | 1 | 1 | 21.90 ± 0.13a | 3.03 ± 0.18a |
| 2 | 2 | 36.34 ± 0.36b | 5.59 ± 0.22b | ||
| 3 | 3 | 40.28 ± 0.09c | 4.54 ± 0.03b | ||
| Average | 32.84 ± 8.38 | 4.39 ± 1.12 | |||
| Flowers | 2 | 4 | 32.43 ± 0.70d | 0.82 ± 0.04c | |
| 3 | 5 | 15.87 ± 0.82e | 0.23 ± 0.01de | ||
| Average | 24.15 ± 9.09 | 0.52 ± 0.33 | |||
| Branches | 1 | 6 | 10.58 ± 0.19f | 0.13 ± 0.02ef | |
| 2 | 7 | 12.20 ± 0.55f | 0.25 ± 0.01d | ||
| 3 | 8 | 3.72 ± 0.08g | 0.16 ± 0.00f | ||
| Average | 8.83 ± 3.91 | 0.18 ± 0.05 | |||
| Erica arborea | Leaves | 4 | 9 | 17.45 ± 0.12e | 2.70 ± 0.06a |
| 5 | 10 | 36.97 ± 0.75b | 4.12 ± 0.03g | ||
| Average | 27.21 ± 10.70 | 3.41 ± 0.78 | |||
| Flowers | 5 | 11 | 24.83 ± 0.26h | 0.44 ± 0.03h | |
| average | 24.83 ± 0.26 | 0.44 ± 0.03 | |||
| Branches | 4 | 12 | 7.37 ± 0.10i | 0.35 ± 0.00h | |
| 5 | 13 | 5.24 ± 0.36j | 0.16 ± 0.01f | ||
| Average | 6.30 ± 1.19 | 0.25 ± 0.10 | |||
| Average leaves | 30.59 ± 10.19 | 4.00 ± 1.17 | |||
| Average flowers | 24.38 ± 8.29 | 0.50 ± 0.30 | |||
| Average branches | 7.82 ± 3.56 | 0.21 ± 0.09 | |||
- Values are means ± standard deviation of three assays. Different letters in the same column mean statistically different results, by Games Howell test (P < 0.05).
- dw, dry weight; GAE, gallic acid equivalent; QE, quercetin equivalent; TFC, total flavonoid content; TPC, total phenolic content.
Antioxidant Capacity
Statistically significant differences in terms of antioxidant capacity were observed (Table 2). On average, leaves presented higher results of TAA followed by flowers, and branches (34.1; 29.5 and 6.3 mg AAE/g dw, respectively). The highest result was obtained in leaves from location 3, while the lowest one, with over 10 times less content than those obtained in leaves, was recorded in the branches from the same location (47.1 and 3.0 mg AAE/g dw, respectively). The highest result was obtained in leaves from location 3, while the lowest one, over 10 times less, was recorded in the branches from the same location (47.1 and 3.0 mg AAE/g dw, respectively). This reflects a high disparity in antioxidant activity within the plant. No results were found in the literature regarding this plant TAA. There are plants with much lower TAA values, like the Indian medicinal plant, Spilanthes calva, with 0.4 mg/g (Sikder et al. 2010), or much higher like the Melothria maderaspatana with 228, 260, 204 and 288 mg AAE/g for leaves, stems, root and fruits, respectively (Sowndhararajan et al. 2010). Upon analysis of results from the RP assay, it appears this plant RP can be influenced by a diversity of factors, because these values vary greatly from 34.33 to 18.1, 26.4 to 18.3 and 9.5 to 4.75 (mg Trolox/g dw) for leaves, flowers and branches, respectively. Interestingly, the higher RP value was found on the leaves from sample 1, one of the samples with the least phenolic and flavonoid content, meaning the phenolics and flavonoids in this sample present a stronger reaction than those of other samples. No RP results for this plant have been published to the best of author's knowledge. Globularia alypum, a plant used in folk medicine, shows an RP value of 0.045 mM Trolox/100 g dw (Harzallah et al. 2010), which is in line with the range determined in this study, from 0.14 to 0.02 mM Trolox/g dw. The FRAP values of the plant branches were neither influenced by collection site nor by species. Also, this plant part showed a much lower FRAP (0.6 mg Trolox/g dw) compared to that obtained from leaves (38.8 mg Trolox/g dw) and flowers (23.9 mg Trolox/g dw), a difference much higher than the one observed in the TPC and TFC assays. Because this assay measures the capacity to reduce the ferric iron (Fe3+) to ferrous iron (Fe2+), in the presence of antioxidants with half reaction reduction potentials above these substances, we can conclude that the phenolics present in the branches have a lower half reduction potential than these substances. To author's knowledge, no results reported were published for this plant for comparison. Regarding other plants, FRAP results expressed in μM Trolox/g dw varied between 6.56 (Surveswaran et al. 2007) and 300 (Wong et al. 2006). Highest and lowest results in the present study were 349.78 and 3.93 μM Trolox/g dw, respectively. Leaves and flowers FRAP data for Erica species studied are in line with these results, but branches are a bit below. The DPPH· radical presents a dark violet color while the ABTS· radical presents a blue color. Both these radicals can react with antioxidants present in plants resulting in a decrease of the color. The concentration required to provide a decrease of 50% is called IC50. Results are represented in Fig. 1 and are labeled by sample ID in order to easily identify and compare with the other antioxidant activity results. In average, and following the trend exhibited in the other assays, leaves' infusions had higher radical scavenging capacity, followed by flowers and branches. However, ABTS IC50 results were much higher compared to DPPH, with results ranging from 66.6 to 537.6 and 296.3 to 4,910.1 μg/mL, respectively. These results mean that these plant antioxidants have a higher affinity toward DPPH radical than toward ABTS. Nevertheless, samples that have lower IC50 for DPPH do not always have lower IC50 for ABTS, indicating some oxidant selectivity. Similar results were found with berry crops (Wang and Jiao 2000). It also appears that location plays a bigger role in ABTS scavenging capacity than it does in DPPH scavenging capacity, although both seem to be influenced by this factor. Regarding other studies, DPPH IC50 for Erica spp. was slightly lower than those obtained in the present study, representing greater scavenging power, which can be explained by different collection sites, extraction procedures and quantification methodologies (Ay et al. 2007; Luís et al. 2009). No results for ABTS were found for this plant. Regarding other plants, ABTS IC50 varied considerably ranging from 9.8 to 580.0 μg/mL (Al‐Mustafa and Al‐Thunibat 2008). Results obtained in leaves and flowers are within this range, but those obtained in branches are much higher.
1,1‐Diphenyl‐2‐picrylhydrazyl (DPPH) (Grey Column) and 2‐2'‐azino‐bis(3 ethylbenzothiazoline‐6‐sulfonic acid) (ABTS) (Grey and White Column) IC50 Values
| Species | Plant part | Location | Sample ID | TAA (mg AAE/g dw) | RP (mg Trolox/g dw) | FRAP (mg Trolox/g dw) |
|---|---|---|---|---|---|---|
| Erica australis | Leaves | 1 | 1 | 26.94 ± 1.19ab | 34.33 ± 0.05a | 21.60 ± 0.12a |
| 2 | 2 | 41.20 ± 3.29acd | 30.97 ± 0.11b | 52.43 ± 0.06b | ||
| 3 | 3 | 47.06 ± 1.05c | 27.95 ± 0.08c | 52.57 ± 0.09b | ||
| Average | 38.40 ± 9.15 | 31.09 ± 2.76 | 42.20 ± 15.45 | |||
| Flowers | 2 | 4 | 36.37 ± 1.81d | 22.98 ± 0.11d | 25.96 ± 0.07c | |
| 3 | 5 | 16.27 ± 0.93e | 18.25 ± 0.09e | 18.91 ± 0.07d | ||
| Average | 26.32 ± 11.08 | 20.61 ± 2.59 | 22.44 ± 3.86 | |||
| Branches | 1 | 6 | 8.67 ± 0.13f | 8.11 ± 0.02f | 0.61 ± 0.00e | |
| 2 | 7 | 9.75 ± 0.33f | 8.85 ± 0.02g | 0.61 ± 0.02e | ||
| 3 | 8 | 3.02 ± 0.32g | 4.75 ± 0.01h | 0.62 ± 0.01e | ||
| Average | 7.15 ± 3.14 | 7.24 ± 1.89 | 0.62 ± 0.01 | |||
| Erica arborea | Leaves | 4 | 9 | 20.08 ± 0.10be | 18.16 ± 0.08e | 20.82 ± 0.24a |
| 5 | 10 | 35.18 ± 1.47d | 26.24 ± 0.16i | 46.40 ± 0.07f | ||
| Average | 27.63 ± 8.33 | 22.20 ± 4.43 | 33.61 ± 14.01 | |||
| Flowers | 5 | 11 | 35.89 ± 1.56d | 26.43 ± 0.24i | 26.69 ± 0.11g | |
| Average | 35.89 ± 1.56 | 26.43 ± 0.24 | 26.69 ± 0.11 | |||
| Branches | 4 | 12 | 6.67 ± 0.13h | 9.50 ± 0.04j | 0.65 ± 0.02e | |
| 5 | 13 | 3.17 ± 0.21g | 5.16 ± 0.01k | 0.62 ± 0.00e | ||
| Average | 4.92 ± 1.93 | 7.33 ± 2.38 | 0.63 ± 0.02 | |||
| Average leaves | 34.09 ± 10.81 | 27.53 ± 6.08 | 38.76 ± 16.22 | |||
| Average flowers | 29.51 ± 11.47 | 22.55 ± 4.11 | 23.85 ± 4.30 | |||
| Average branches | 6.26 ± 3.09 | 7.28 ± 2.18 | 0.62 ± 0.01 | |||
- Values are means ± standard deviation of three assays. Different letters in the same column mean statistically different results, by Games and Howell test (P < 0.05).
- AAE, ascorbic acid equivalent; dw, dry weight; FRAP, ferric‐reducing antioxidant power; RP, reducing power; TAA, total antioxidant activity.
On average, E. australis L. leaves showed better results in all studies especially in RP. In the other studies, the averages are quite similar mostly because of the lower performance of the sample from location 1, which showed about half of the power of the other two E. australis L. samples. Flowers of E. arborea L. performed better in RP and FRAP assays and similar on the other assays. Regarding branches, E. australis L. showed better results in TPC, TAA, DPPH and ABTS assays; however, the averages are not significantly different because of the lower performance of branches from location 3.
The current study is highly significant because different parts of two Erica species were analyzed for the first time using varied assays such as TAA, RP, FRAP antioxidant activities and ABTS radical scavenging activities. The studied plant parts performed different in the assays with some oxidant selectivity. This could be due to the difference in the structure and/or amount of antioxidants present in the plant parts. However, a better understanding of the antioxidant activity of the plant is still required to use them for commercial or fundamental health applications.
Correlations and HCA
Coefficients of determination (R2) were computed to measure the strength of linear relationships between the different methods (Table 3). TPC correlates strongly with all methods especially with TAA (0.952) and FRAP (0.916). The best correlations with TFC were obtained for FRAP (0.771), followed by TAA (0.561) and RP (0.562). FRAP and TAA assays present a strong linear relationship (0.884), while RP R2 varied between 0.562 for TFC and 0.809 for TAA. Also, there is a good linear relationship between DPPH and ABTS (0.668).
- ABTS, 2‐2'‐azino‐bis(3 ethylbenzothiazoline‐6‐sulfonic acid); DPPH, 1,1‐diphenyl‐2‐picrylhydrazyl; FRAP, ferric‐reducing antioxidant power; RP, reducing power; TAA, total antioxidant activity; TFC, total flavonoid content; TPC, total phenolic content.
In order to group the different results by similarity, and see which factors influenced them the most, HCA was performed on samples and on assays. Upon application of this tool, samples (Fig. 2A) were grouped in two clusters, with all branches in the first (CLA1) and leaves and flowers together in the second (CLA2). HCA confirmed that plant part factor was more responsible for the differences than species or location, and also flowers are closer to leaves than to branches. Regarding methods (Fig. 2B), HCA supported the results obtained by the correlations, showing that TAA is mainly due to TPC, with TFC playing a lesser role, and the best method to measure it is FRAP.
Dendrogram Built by Hierarchical Cluster Analysis with All Samples (A) and Parameters (B) Using Average Link between Groups Method and Euclidean Squared Distance
ABTS, 2‐2'‐azino‐bis(3 ethylbenzothiazoline‐6‐sulfonic acid); DPPH, 1,1‐diphenyl‐2‐picrylhydrazyl; FRAP, ferric‐reducing antioxidant power; RP, reducing power; TAA, total antioxidant activity; TFC, total flavonoid content; TPC, total phenolic content.
Conclusions
The antioxidant capacity is mainly influenced by the plant part studied, which means antioxidants present in them are probably different in structure and amount. Overall, the findings of this study support the view that Erica plants are promising potential sources of antioxidants, especially their leaves and flowers, and may be efficient as preventive agents in the pathogenesis of some diseases. However, the strength of the existing data is not enough to suggest a reasonable mode of action for antioxidant effects. The data of this study may just enrich the existing comprehensive data of antioxidant capacity of Erica plant materials.
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