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Article

Determination of Antioxidant, Phenolic Compound and Mineral Contents in Olive Leaves by Chromatographic and Spectrophotometric Methods

by
Fahad Aljuhaimi
1,
Isam A. Mohamed Ahmed
1,
Mehmet Musa Özcan
2,*,
Nurhan Uslu
2 and
Emad Karrar
3
1
Department of Food Science & Nutrition, College of Food and Agricultural Sciences, King Saud University, Riyadh 11451, Saudi Arabia
2
Department of Food Engineering, Faculty of Agriculture, Selcuk University, Konya 42031, Turkey
3
Department of Plant Sciences, North Dakota State University, Fargo, ND 58108, USA
*
Author to whom correspondence should be addressed.
Processes 2025, 13(9), 2785; https://doi.org/10.3390/pr13092785
Submission received: 10 July 2025 / Revised: 23 July 2025 / Accepted: 27 August 2025 / Published: 30 August 2025
(This article belongs to the Section Biological Processes and Systems)
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Versions Notes

Abstract

In this study, changes in total phenolic content, total flavonoids, tannin content and phenolic constituents, and mineral content of the leaves of five olive varieties (Ayvalık, Gemlik, Sarıulak, Çöpaşı and Delice) collected in Mersin province in Turkey were investigated. Tannin contents of olive leaves extracts were determined to be between 1.73 (Sarıulak) and 5.33% (Çöpaşı). Total phenolic and flavonoid amounts in olive leaves were assayed to be between 2122.02 (Sarıulak) and 2338.69 mgGAE/100 g (Çöpaşı), and between 9010.71 (Sarıulak) and 18,910.71 mg quercetin equivalent/100 g (Çöpaşı), respectively. Also, the antioxidant activities of methanol extracts of the olive leaves were discovered to be between 0.85 mmolTE/kg (Gemlik) and 21.04 mmolTE/kg (Sarıulak). The phenolic components of the olive leaves studied showed differences depending on the variety of olive. Catechin, rutin, and 3,4-dihydroxybenzoic acid were the most abundant phenolics in leaf extracts. Also, “Delice” olive leaves in the wild form generally had more caffeic acid, syringic acid and rutin, compared to the other olive varieties studied. While the olive leaves were determined to be high in macroelements, the microelement contents detected in olive leaves were low. In general, there was a linear connection between the total phenols and antioxidant activities of leaf samples. This connection was also exhibited between the total flavonoid content and antioxidant activities of olive leaves (except for Sarıulak).

1. Introduction

The olive tree is native to the Mediterranean region and is grown on 8 million hectares of land in Mediterranean countries [1,2]. Olive has been an important food source for people throughout the history of civilization due to both its fruit and its oil [2,3]. Olive fruit, olive oil and leaves have been accepted as important components of medicine and healthy nutrition due to their pharmacological properties, including antioxidant, anti-inflammatory, anti-atherogenic, anti-cancer, antimicrobial, and antiviral activities, their hypolipidemic and hypoglycemic effect, and their phenolic content [1,2,3]. Olive leaves are considered a good source of bioactive constituents due to their polyphenols [4]. Mourtzinos et al. [5] found that encapsulation of olive leaf extracts rich in oleuropein with the help of beta-cyclodextrin increased the solubility of polyphenols in the leaf extract in aqueous media. The olive oil industry generates several byproducts including olive pomace, wastewater and olive leaves, represented by a mixture of leaves and branches obtained from olive tree pruning and harvesting as well as olive milling. During harvest, olives may contain leaves. These leaves must be removed before processing into oil. Therefore, these removed leaves are considered a byproduct of olive oil processing [6]. Olive leaves are rich in phenolic compounds that exhibit a wide range of biological activities, including antioxidant, antimicrobial, antihypertensive, anti-inflammatory, and cardioprotective capacities [7,8,9]. Among the phenolic compounds present in olive leaves, the most common is oleuropein, but hydroxytyrosol, verbascoside, apigenin-7-glucoside, and luteolin-7-glucoside are also found in olive leaf extracts [3]. Approximately 98% of the total olive leaf in the world is obtained during the pruning of olive trees grown in the Mediterranean region [10]. The majority of pomace, black water and leaves are formed as byproducts during olive oil production [11]. The amount and structure of phenolic components found in fruit, leaves and stems of the olive plants vary greatly between olive tissues [4]. Olive leaf has antioxidant and hypoglycemic effects [10,11,12,13,14,15]. Korukluoglu et al. [16] investigated the antimicrobial effect of olive leaf extract obtained by using different solvents on several microorganisms. According to the results of their research, they stated that Saccharomyces cerevisiae is the most resistant species to olive leaf extract, and olive leaf extracts can be used as natural preservatives in various industries due to their antimicrobial properties. They are not only used in medicine, food additives, dietary supplements, cosmetics and pharmaceuticals by some industries, but also in extending the shelf life of foods [17,18]. The determinants of phenolic compounds of olive leaves vary between abiotic (moisture deficiency, salinity, fertilization, geographical region, sampling time, sun exposure, frost stress) and biotic (fungi, bacteria, genotype, leaf age, alternate types) depending on stress factors [19]. The most important step in determining the phenolic composition of leaves correctly is the extraction of phenolic compounds. It is stated that factors such as solvent type and amount, temperature, pH, sample particle size, which vary according to the methods used for the extraction of phenolic constituents, have an effect on the extraction efficiency [7]. The interest of various researchers in olive leaf, which contains phenolic components such as oleuropein, flavonoids, and flavonols, has increased [20,21,22]. Today, products of olive leaves used as herbal tea and food supplements are available all over the world, and these products can be in the form of completely dried leaves, powder, extract, and tablets [19,23]. It has been stated that olive leaf extracts can be used as an alternative in cracker production because they both contain functional components and extend the shelf life of the products [24]. Olive byproducts such as extra virgin olive oil and table olives attract great attention from consumers and users. [25,26]. There are studies using olive leaf extract to improve the quality and stability of various food products such as meat [27,28] and vegetable oils [29,30]. The main active phenolic compound that gives bitterness to olive leaves is oleoropein, along with hydroxytyrosol, which can constitute about 6–9% of the dry matter of the leaf [31,32]. Olive leaves, considered waste during the olive harvest, have been identified as providing a good source of raw materials for the economy and related sectors, and their bioactive properties and phenolic compounds have been identified. The goal of the current investigation was to establish changes in total phenolic content, total flavonoid content, tannin content and phenolic constituents, and mineral contents leaves collected from five olive varieties (Ayvalık, Gemlik, Sarıulak, Çöpaşı and Delice) from Mersin province in Turkey.

2. Materials and Methods

2.1. Materials

Leaves were collected from Ayvalık, Gemlik, Sarıulak, Çöpaşı and Delice olive trees grown in Mersin (Mut and Silifke) in May 2024. Olive leaves are below (Figure 1):
After the leaves were collected, they were brought to the laboratory in a cold bag. The olive leaves brought to the laboratory were dried in the open air for 1 month, and the dried olive leaves were stored at 4 °C for analysis.
Reagents: All the chemicals used in this study were of high purity and grade.

2.2. Methods

2.2.1. Moisture Content

The amounts of moisture of olive leaf samples were monitored using a KERN & SOHN GmbH infrared moisture analyser. Moisture analysis was performed to provide results based on dry matter.

2.2.2. Tannin Content

Tannin amounts in leaves were recorded according to the method described by Atanassova and Christova-Bagdassarian [33].

2.2.3. Extraction Process

After olive leaves (0.5 g) were mixed with 5 mL methanol/water (80:20, v/v), the mixture was stirred using a vortex for 1 min. Then, it was sonicated in a water bath (Wise Bath) for 10 min and centrifuged at 6000 rpm for 10 min. The supernatant was removed and these steps were repeated twice. Finally, the extract was filtered using a 0.45 µm syringe filter before analysis, and the extract was filtered with Whatman filter paper [15].

2.2.4. Total Phenolic Content

The total phenol values in olive leaf extracts were detected by using Folin Ciocalteu (Sigma, Nagano, Japan) reagent according to the method explained by Yoo et al. [34]. Extract (0.5 mL) was mixed with 2.5 mL of Folin Ciocalteu and 1.5 mL of sodium carbonate solution. The absorbance of the samples was recorded at 725 nm. Results obtained are expressed as mg gallic acid equivalent (GAE)/100 g (dry weight).

2.2.5. Total Flavonoid Content

Total flavonoid contents of olive leaf extracts were established according to the method stated by Hogan et al. [35]. The absorbance of the samples was recorded at 510 nm. Calculated results are defined as mg catechin (CE)/100 g (dw).

2.2.6. Antioxidant Activity

The antioxidant activity of the olive leaves was tested according to the DPPH (Sigma) method specified by Lee et al. [36]. Extracts (0.1 mL) were mixed with 2 mL of DPPH solution and kept in the dark for 30 min at room temperature, after which the absorbance values of the samples were measured at 517 nm. The results are given as mmol trolox (TE)/kg dw.

2.2.7. Determination of Phenolic Compounds

A high-performance liquid chromatography (HPLC Shimadzu LC 10A vp, Kyoto, Japan)-equipped column (5 µm, 25 cm × 4.6 mm) (Inertsil ODS3 analytical column) and Shimadzu SPD-M20 A Diode Array Detector at 280 and 330 nm were used to determine phenolic compounds in olive leaf extracts [15]. Gradient elution was performed for separation and a mixture of 0.05% acetic acid in water (A) and acetonitrile (B) was used as the mobile phase. The following elution programme was employed: 0–0.10 min 8% B; 0.10–2 min 10% B; 2–27 min 30% B; 27–37 min 56% B; 37–37.10 min 8% B; 37.10–45 min 8% B. The injection volume and total running time per sample were 20 µL and 60 min, respectively. Phenolic compounds were determined according to the retention time and absorption spectra of peaks of standard compounds. The total area under the peak was used to quantify each phenolic.

2.2.8. Determination of Minerals

Olive leaf powder (0.5 g), dried in a drying cabinet at 70 °C to constant weight, was incinerated using 5 mL of 65% HNO3 (Merck, Darmstadt, Germany) and 2 mL of 35% H2O2 (Merck, Darmstadt, Germany) in a closed microwave system. The volume of the microwave-burned olive leaf solution was completed to 20 mL with distilled water and the mineral contents of the samples were analyzed by ICP-OES (Agilent-5110, Santa Clara, CA, USA).

2.2.9. Working Conditions of ICP-OES

RF power of instrument (ICP-OES) and plasma gas flow rate (Ar): 0.7–1.5 kw (1.2–1.3 kw for Axial) and 10.5–15 L/min. (radial) 15 “(Axial), respectively. Auxiliary gas flow rate (Ar) was 1.5”. Viewing height and copy and reading time were 5–12 mm and 1–5 s (max. 60 s), respectively. Copy time was applied as 3 s (max. 100 s).

2.3. Statistical Analyses

One-way ANOVA was carried out by taking the averages of the data from triplicate analyses. Significant variations among olive leaf extract type results were calculated by Duncan’s Multiple Range Test (p < 0.05). Principal component analysis (PCA) was performed according to Abdi and Williams [37].

3. Results and Discussion

3.1. Chemical and Bioactive Properties of Methanol Extracts of Olive Leaves

The chemical and bioactive properties of methanol extracts of the five varieties of olive leaves (Ayvalık, Gemlik, Sarıulak, Çöpaşı and Delice) are provided in Table 1. The moisture contents of the leaves were found to be between 6.92% (Delice) and 8.13% (Çöpaşı), while tannin contents of extracts varied between 1.73% (Sarıulak) and 5.33% (Çöpaşı), total phenolic values of olive leaf extracts were found to be between 2122.02 mg gallic acid equivalent (GAE)/100 g (Sarıulak) and 2338.69 mgGAE/100 g (Çöpaşı), total flavonoid amounts of methanol extracts of five olive leaves were between 9010.71 (Sarıulak) and 18,910.71 mgQE/100 g (Çöpaşı), and antioxidant activity values of extracts were established to be between 20.85 mmolTE/kg (Gemlik) and 21.04 mmolTE/kg (Sarıulak). As seen in Table 1, the highest moisture, tannin, total phenol and total flavonoid amounts were established to be in “Çöpaşı” olive leaf, followed by “Ayvalık”, “Delice”, “Gemlik” and “Sarıulak” olive leaf extracts. The tannin contents of wild “Delice” olive leaves were statistically different (p < 0.05). In general, there was a linear relationship between the total phenol contents and antioxidant activities of the olive leaves. Olive leaves are rich in total phenols and flavonoids. Silva et al. [38] determined 11.6–17.4 and 11.7–40.1 g/kg total phenols in fresh and dried olive leaves, respectively. Boudhioua et al. [39] determined 13.80 mgGAE/g (dw) total phenols in a Tunisian “Chemlali” olive variety leaf. Vassiliki et al. [22] determined 68.9–483.1 mg/g (dw) total phenols in olive leaf extracts. Debib and Boukharem [40] reported that methanol extract of “Chemlali” olive leaf contained 21.47 mgGAE/g total phenols and 17.64 mgCE/g total flavonoids. Edziri et al. [2] determined 18.96–47.47 mgGAE/g total phenols and 3.08–7.29 mgCE/g total flavonoids in four olive cultivars’ methanolic extract, respectively. Total phenolic values of ethanol, methanol and water extracts of fresh olive leaves were found to be 266.33, 317.33 and 387.00 µgGAE/g, respectively [10]. Akbaş et al. [41] determined 2121.88–778.13, 884.90, 963.54 and 664.58 mgGAE/100 g total phenols in Akdeniz yerli, Sarıulak, Topakaşı, Gemlik and Yağlık olive variety leaves. Zuntar et al. [42] determined 5.32–20.61 mgGAE/g total phenols and 24.78–33.31 µmolTAE/g antioxidant capacity (DPPH) values in olive leaf extracts. Akbaş et al. [41] determined 84.24, 85.46, 85.72, 85.90 and 70.89% antioxidant activity values in Akdeniz Yerli, Sarıulak, Topakaşı, Gemlik and Yağlık olive leaves. Total flavonoid contents of ethanol, methanol and water extracts of fresh olive leaves were determined to be 62.92, 86.00 and 141.17 µg/g, respectively [10]. Özcan et al. [26], in their studies examining the effect of harvest time and varieties on the bioactive properties of olive fruit and leaves, observed the highest total phenols (2657.81 mg/100 g) and antioxidant activity (83.33%) in Ayvalık olive leaves harvested in December and Edremit and Tavşanyüreği olive leaves harvested in November and December, respectively. In general, the polyphenol contents as well as the degree of hydroxylation of phenolic compounds have been reported to have a strong effect on DPPH radical scavenging activity [43]. It has been reported that olive leaf has antioxidant properties associated with oleuropein and also has antioxidant activity through scavenging the superoxide anion of caffeic acid [44]. The results showed significant differences from the total flavonoid contents of olive leaves (5.57 to 25.64 µg/g) determined by Salah et al. [45]. When the results were compared with the literature, some quantitative differences were detected. Possible reasons for these differences might be due to olive variety, harvesting time and solvent differences [41]. Rahmaniana et al. [46] stated that olive variety, climatic conditions, and extraction procedures had an effect on the chemical composition of olive leaves.

3.2. Phenolic Contents of Methanol Extracts of Olive Leaves

The phenolic compounds and their amounts in methanol extracts of five olive leaf varieties are offered in Table 2. In general, the phenolics of the olive leaves studied show differences depending on the variety of olive (Figure 2). As seen in Table 2, catechin, rutin, and 3,4-dihydroxybenzoic acid were the major phenols of the studied leaves.
In addition, it is seen that olive leaves are rich in flavonoids and phenolic acids. The gallic and 3,4-dihydroxybenzoic acid values ranged between 32.06 (Delice) and 117.51 mg/100 g (Gemlik), and between 114.05 (Sarıulak) and 185.43 mg/100 g (Çöpaşı), respectively. Also, while caffeic acid amounts were between 50.04 (Ayvalık) and 142.83 mg/100 g (Delice), syringic acid values were determined to be between 36.81 (Çöpaşı) and 210.96 mg/100 g (Delice). In addition, p-coumaric and ferulic acid amounts were between 23.28 (Çöpaşı) and 51.45 mg/100 g (Delice), and between 42.09 (Delice) and 55.58 mg/100 g (Sarıulak), respectively. The cinnamic acid amounts ranged from 5.41 mg/100 g (delice) to 33.93 mg/100 g (Çöpaşı). Among flavonoids, catechin contents were found to have the highest amounts in olive leaves, which were between 222.59 mg/100 g (Gemlik) and 582.59 mg/100 g (Ayvalık). Rutin and resveratrol amounts in methanol extracts of the five olive leaf varieties were found to be between 149.35 (Ayvalık) and 418.55 mg/100 g (Delice), and between 17.19 (Gemlik) and 40.20 mg/100 g (Ayvalık), respectively, while quercetin values of extracts were found to be between 74.30 (Delice) and 158.00 mg/100 g (Çöpaşı), and kaempferol values were recorded between 8.42 (Sarıulak) and 28.89 mg/100 g (Delice). “Çöpaşı” olive leaf had the highest amounts of gallic acid and quercetin. Table 2 shows that olive leaves are rich in phenolic components, regardless of the variety. The amounts of phenolic compounds differed depending on the cultivars. 3,4-dihydroxybenzoic acid, catechin, caffeic acid, syringic acid and rutin were significantly localized in the wild “Delice” olive leaf. In addition, the wild “Delice” olive leaf generally had more caffeic acid, syringic acid and rutin compared to other olive varieties studied. The phenolic compound amounts in Çöpaşı and Delice olive leaves were generally higher than other olive leaf varieties. Oleuropein and its derivatives (hydroxytyrosol and tyrosol), caffeic acid, p-coumaric acid, vanillic acid, vanillin, luteolin, rutin, luteolin-7-glucoside, apigenin-7-glucoside and diosmetin-7-glucoside are the main phenolic components of olive leaf [47]. Methanol olive leaf extract contained 92.5 mg/g oleuropein, 70.6 mg/g luteolin-4-0-glucoside, 67.8 mg/g luteolin-7-0-glucoside, 53.5 mg/g luteolin and 18.3 mg/g hydroxytyrosol [48]. Luteolin-7-0-glucoside methanol has been elsewhere reported to be a component of olive leaf extracts [49]. The oleuropein values of olive leaves were determined to lie between 5.6 and 108.6 mg/g (dw) [50,51,52]. Akbaş et al. [41] determined 222.06–347.18 mg/100 g gallic acid, 184.18–363.55 mg/100 g 3,4-dihydroxybenzoic acid, 73.09–693.92 mg/100 g (+)-catechin, 725.21–1583.90 mg/100 g 1,2-dihydroxybenzene, 83.93–367.74 mg/100 g syringic acid, 109.31–251.65 mg/100 g caffeic acid, 72.79–439.71 mg/100 g rutin trihydrate, 23.28–54.27 mg/100 g p-coumaric acid, 43.10–300.75 mg/100 g trans-ferulic acid, 122.53–1000.83 mg/100 g apigenin-7-glucoside, 91.64–1104.66 mg/100 g oleuropein, 560.98–2066.91 mg/100 g quercetin, 38.07–355.23 mg/100 g trans-cinnamic acid, 221.74–298.17 mg/100 g naringenin, 156.29–1000.84 mg/100 g kaempferol and 868.70–1636.74 mg/100 g isorhamnetin in Akdeniz yerli, Sarıulak, Topakaşı, Gemlik and Yağlık olive leaf varieties. Edziri et al. [2] determined 75.7–91.31 µg/g hydroxytyrosol, 83.5–141.33 µg/g tyrosol, 54.8–83.76 µg/g 4-hydroxybenzoic acid, 145.6–248.64 µg/g rutin, 112.98–217.26 µg/g luteolin-7-0-glucoside, 312.56–419.08 µg/g apigenin-7-0-glucoside, 245.5–520.11 µg/g oleuropein, and 21.65–43.27 µg/g apigenin in methanol extracts of Chetoui, Meski, Jarbouii and Ouslati olive leaves. In general, the amounts of phenolic components in the leaves of olive varieties show significant differences compared to each other. The amounts of phenolic compounds in olive leaves in our study differed from the results of Edziri et al. [2] and Akbaş et al. [41]. These differences in phenolic compounds in olive leaves may be due to variety, cultivated form, genetics, climatic factors, age of leaves, and irrigation situation.

3.3. Mineral Contents of Methanol Extracts of Five Olive Leaf Varieties

The mineral contents of the five olive leaf varieties are represented in Table 3. The mineral values of the leaves showed some changes depending on olive varieties. While P amounts in olive leaves varied between 615.88 (Delice) and 1276.87 mg/kg (Sarıulak), K amounts of leaves were determined to be between 4311.82 (Delice) and 7483.67 mg/kg (Sarıulak). Ca and Mg contents of the five olive leaf varieties were establishedto be between 17,355.82 mg/kg (Çöpaşı) and and 460 mg/kg (Delice) to 1389.39 mg/kg (Gemlik) and 2331.36 mg/kg (Çöpaşı), respectively. Also, while Na amounts in olive leaves were recorded between 30.00 (Gemlik) and 1325.49 mg/kg (Ayvalık), S amounts in olive leaves were found to be between 1094.39 (Sarıulak) and 1412.45 mg/kg (Gemlik). Fe and Cu amounts ranged between 44.09 mg/kg (Sarıulak) and 133.82 mg/kg (Delice), and 3.94 (Delice) and 22.62 mg/kg (Gemlik), respectively. Mn values in olive leaves were found to be between 16.85 mg/kg (Delice) and 27.57 mg/kg (Çöpaşı). Table 3 shows that olive leaves were rich in macroelements. In particular, the Ca contents of the leaves of all cultivars were determined to be quite high compared to other minerals. The highest Ca was detected in “Gemlik” and wild “Delice” cultivars, followed by K, P, Mg, and S in decreasing order. The highest Na value was detected in “Ayvalık” leaf, while the Na contents of other cultivars decreased significantly. This situation is probably related to the soil nutrient element in which the “Ayvalık” olive tree grows [41]. In the wild “Delice” olive leaf, P, K and Cu contents were determined to be at the lowest levels compared to other olive leaves, while Fe and Zn were found in the highest amounts. The highest concentrations of Zn and B were identified in Gemlik olive leaf. While the olive leaves were determined to be high in macroelements, the micronutrient element contents of the olive leaves were low. In a previous study, Bahloul et al. [53] determined 9.25–10.39 mg/g Ca, 4.47–9.14 K, 1.50–3.00 Mg, and 0.34–1.51 mg/g Na in Chemlali, Chemchali, Chetoui and Zarrazi olive leaves. In another study, Akbaş et al. [41] determined 10,210.84–18,113.36 mg/kg Ca, 6.46–18.66 B, 6.77–19.70 Cu, 97.05–206.30 Fe, 8943.41–13,663.38 K, 915.92–1993.06 Mg, 3.13–25.33 Mn, 381.49–626.82 Na, 1091.17–1620.43 P, 890.88–1800.62 S and 11.35–24.96 mg/kg Zn in Akdeniz yerli, Sarıulak, Topakaşı, Gemlik and Yağlık olive leaf varieties. Khanum et al. [54] determined 7.70–9.93 g/kg K, 12.90- 20.36 g/kg Ca, 0.80–2.73 g/kg Mg, 286.7–426.7 g/kg Na, 54.63–73.56 g/kg Fe, 26.46–34.60 g/kg Mn, 18.33–28.23 g/kg Zn, and 10.93–25.60 g/kg Cu in in eight olive leaf varieties grown in Pakistan’s “Olive Valley”. In general, the dominant elements were the same when compared to the literature. Partial differences in the mineral values of olive leaves might probably be due to variety, age of the olive tree, presence of soil nutrients, moisture content of the soil, collection date of the leaves, climatic factors, and genetic structure of the olive trees.

4. Principal Component Analysis (PCA)

Principal component analysis (PCA) was carried out to evaluate the effect of different olive varieties on phenolic compounds (Figure 3). PCA modeling exhibited about 56.777% of explained variance for PC1 and 25.273% of variance for PC2, which is shown in Table 4. A high positive correlation was found among caffeic acid (0.861), syringic acid (0.979), rutin (0.882), and coumaric acid (0.830) with PC1, while PC2 showed a positive correlation with resveratrol (0.868), kaempferol (0.764), and catechin (0.759). Delice olive was located in the positive area of both PC1 and PC2, while Sarıulak and Gemlik olives were located in the negative areas of PC1 and PC2. Delice olives were rich in syringic acid, caffeic acid and rutin. Çöpaşı olive leaves contained higher amounts of quercetin and 3,4-dihydroxybenzoic acid. In addition, the highest gallic acid content was observed in Gemlik olives.

5. Conclusions

In general, there was a linear connection between the total phenols and antioxidant activities in leaf samples. This connection was exhibited between the total flavonoid content and antioxidant activities of olive leaf varieties (except for Sarıulak). Catechin, rutin, and 3,4-dihydroxybenzoic acid were the major phenolic constituents of all olive leaves studied (p < 0.05). Also, Çöpaşı olive leaf had the highest concentrations of gallic acid and quercetin. Mineral amounts in the olive leaves showed some differences depending on olive varieties. While the olive leaves were determined to be high in macroelements, the micronutrient element contents of olive leaves were low. The highest Na was found in Ayvalık olive leaf compared to the other olive varieties studied. In general, there was a linear connection between the total phenol and antioxidant activities of leaf samples. This connection was pronounced between the total flavonoid contents and antioxidant activities of olive leaves (except for Sarıulak).

Author Contributions

Validation, editing, F.A.; Investigation, software, editing, I.A.M.A.; Methodology, software, writing, editing, M.M.Ö.; Formal analysis, N.U.; Validation, software, E.K.; All authors have read and agreed to the published version of the manuscript.

Funding

This study was supported and funded (ORF-2025-83) by King Saud University, Riyadh, Saudi Arabia.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author(s).

Acknowledgments

The authors appreciate the support from the Ongoing Research Funding Program, (ORF-2025-83), King Saud University, Riyadh, Saudi Arabia.

Conflicts of Interest

The authors declare no competing.

References

  1. Sanchez-Gutierrez, M.; Gomez-Garcia, R.; Carrasco, E.; Rodriguez, A.; Pintado, M. Bioactive. Potential of Olive Leaf By-Product Throughout In Vitro Gastrointestinal Digestion. Foods 2025, 14, 563. [Google Scholar] [CrossRef]
  2. Ferreira, D.M.; de Oliveira, N.M.; Chéu, M.H.; Meireles, D.; Lopes, L.; Oliveira, M.B.; Machado, J. Updated Organic Composition and Potential Therapeutic Properties of Different Varieties of Olive Leaves from Olea europaea. Plants 2023, 12, 688. [Google Scholar] [CrossRef] [PubMed]
  3. Özcan, M.M.; Matthaus, B. A review: Benefit and bioactive properties of olive (Olea europaea L.) leaves. Eur. Food Res. Technol. 2017, 243, 89–99. [Google Scholar] [CrossRef]
  4. Jilani, H.; Cilla, A.; Barbera, B.; Hamdi, M. Improved bioaccessibility and antioxidant capacity of olive leaf (Oleo europea L.) polyphenols through biosorption on Saccharomyces cerevisae. Ind. Crops Prod. 2016, 84, 131–138. [Google Scholar] [CrossRef]
  5. Mourtzinos, I.; Salta, F.; Yannakopoulou, K.; Chiou, A.; Karathanos, V.T. Encapsulation of olive leaf extract in β-cyclodextrin. J. Agric. Food Chem. 2007, 55, 8088–8094. [Google Scholar] [CrossRef]
  6. Souılem, S.; Fki, I.; Kobayashı, I.; Khalıd, N.; Neves, M.A.; Isoda, H.; Sayadı, S.; Nakajıma, M. Emerging technologies for recovery of value-added components from olive leaves and their applications in food/feed industries. Food Bioprocess Technol. 2017, 10, 229–248. [Google Scholar] [CrossRef]
  7. Clodoveo, M.L.; Crupi, P.; Annunziato, A.; Corbo, F. Innovative Extraction Technologies for Development of Functional Ingredients Based on Polyphenols from Olive Leaves. Foods 2022, 11, 103. [Google Scholar] [CrossRef]
  8. Khemakhem, I.; Abdelhedı, O.; Trıguı, I.; Ayadı, M.A.; Bouazız, M. Structural, antioxidant and antibacterial activities of polysaccharides extracted from olive leaves. Int. J. Biol. Macromol. 2018, 106, 425–432. [Google Scholar] [CrossRef]
  9. Orak, H.H.; Karamać, M.; Amarowıcz, R.; Orak, A.; Penkacık, K. Genotype-related differences in the phenolic compound profile and antioxidant activity of extracts from olive (Olea europaea L.) leaves. Molecule 2019, 24, 1130. [Google Scholar] [CrossRef]
  10. Zeitoun, M.A.M.; Mansour, H.M.M.; Ezzat, S.; El Sohaimy, S.A. Effect of Pretreatment of Olive Leaves on Phenolic Content and Antioxidant Activity. Am. J. Food Technol. 2017, 12, 132–139. [Google Scholar] [CrossRef]
  11. Menduh, B. Zeytin, Zeytin Çekirdeği ve Zeytin Yaprağindaki Oleuropein Bileşiginin Izolasyonu ve Miktarlarinin Karşilaştirilmasi. Master’s Thesis, Balıkesir Universitesi Fen Bilimleri Enstitusü, Balıkesir, Turkey, 2015; pp. 1–46. [Google Scholar]
  12. Ryan, D.; Antolovich, M.; Prenzler, P.; Robards, K.; Lavee, S. Biotransformations of phenolic compounds in Olea europaea L. Sci. Hort. 2002, 92, 147–176. [Google Scholar] [CrossRef]
  13. Visioli, F.; Poli, A.; Galli, C. Antioxidant and other biological activities of phenols from olives and olive oil. Med. Res. Rev. 2002, 22, 65–75. [Google Scholar] [CrossRef] [PubMed]
  14. Soni, M.G.; Burdock, G.A.; Christian, M.S.; Bitler, C.M.; Crea, R. Safety assessment of aqueous olive pulp extract as an antioxidant or antimicrobial agent in foods. Food Chem. Toxicol. 2006, 44, 903–915. [Google Scholar] [CrossRef] [PubMed]
  15. Talhaoui, N.; Gómez-Caravaca, A.M.; Leon, L.; De la Rosa, R.; Segura-Carretero, A.; Fernández-Gutiérrez, A. Determination of phenolic compounds of ‘Sikitita’olive leaves by HPLC-DAD-TOF-MS. Comparison with its parents ‘Arbequina’and ‘Picual’olive leaves. LWT-Food Sci. Technol. 2014, 58, 28–34. [Google Scholar] [CrossRef]
  16. Korukluoglu, M.; Sahan, Y.; Yigit, A.; Karakas, R. Antifungal activity of olive leaf (Olea europaea L.) extracts from the trilye region of Turkey. Ann. Microbiol. 2006, 56, 359–362. [Google Scholar] [CrossRef]
  17. Zhao, H.; Kim, Y.; Avena-Bustillos, R.J.; Nitin, N.; Wang, S.C. Characterization of California Olive Pomace Fractions and Their in Vitro Antioxidant and Antimicrobial Activities. LWT 2023, 180, 114677. [Google Scholar] [CrossRef]
  18. Botsoglou, E.; Govaris, A.; Christaki, E.; Botsoglou, N. Effect of dietary olive leaves and/or α-tocopheryl acetate supplementation on microbial growth and lipid oxidation of turkey breast fillets during refrigerated storage. Food Chem. 2010, 121, 17–22. [Google Scholar] [CrossRef]
  19. Talhaoui, N.; Taamalli, A.; Gomez-Caravaca, A.M.; Fernandez-Gutierrez, A.; Segura-Carretero, A. Phenolic compounds in olive leaves: Analytical determination, biotic and abiotic influence, and health benefits. Food Res. Int. 2015, 77, 92–108. [Google Scholar] [CrossRef]
  20. Al Juhaimi, F.; Özcani, M.M.; Uslu, N.; Ghafoor, K.; Babiker, E.E.; Adiamo, O.Q.; Alsawmahi, O.N. The effects of conventional heating on phenolic compounds and antioxidant activities of olive leaves. J. Food Sci. Technol. 2018, 55, 4204–4211. [Google Scholar] [CrossRef]
  21. Petridis, A.; Therios, I.; Samouris, G.; Tananaki, C. Salinityinduced changes in phenolic compounds in leaves and roots of four olive cultivars (Olea europaea L.) and their relationship to antioxidant activity. Environ. Experimental Bot. 2012, 79, 37–43. [Google Scholar] [CrossRef]
  22. Selim, S.; Albqmi, M.; Al-Sanea, M.M.; Alnusaire, T.S.; Almuhayawi, M.S.; AbdElgawad, H.; Al Jaouni, S.K.; Elkelish, A.; Hussein, S.; Warrad, M.; et al. Valorizing the usage of olive leaves, bioactive compounds, biological activities, and food applications: A comprehensive review. Front. Nutr. 2022, 9, 1008349. [Google Scholar] [CrossRef]
  23. Tsimidou, M.Z.; Papoti, V.T. Bioactive Ingredients in Olive Leaves. In Olives and Olive Oil in Health and Disease Prevention; Preedy, V.R., Watson, R.R., Eds.; Elsevier: Amsterdam, The Netherlands, 2010; pp. 349–356. [Google Scholar]
  24. Palmeri, R.; Monteleone, J.I.; Barbera, A.C.; Maucieri, C.; Todaro, A.; Giannone, V.; Spagna, G. Production of Functional Crackers Enriched with Olive (Olea europaea L.) Leaf Extract. Int. J. Nutr. Food Eng. 2016, 3. [Google Scholar]
  25. Sousa, A.; Malheiro, R.; Casal, S.; Bento, A. Antioxidant activity and phenolic composition of Cv. Cobrançosa olives affected through the maturation process. J. Functional Foods 2014, 11, 20–29. [Google Scholar] [CrossRef]
  26. Özcan, M.M.; Fındık, S.; Al Juhaimi, F.; Ghafoor, K.; Babiker, E.E.; Adiamo, O.Q. The effect of harvest time and varieties on total phenolics, antioxidant activity and phenolic compounds of olive fruit and leaves. J. Food Sci. Technol. 2019, 56, 2373–2385. [Google Scholar] [CrossRef] [PubMed]
  27. Hayes, J.E.; Stepanyan, V.; Allen, P.; O’Grady, M.N.; Kerry, J.P. Effect of lutein, sesamol, ellagic acid and olive leaf extract on the quality and shelf-life stability of packaged raw minced beef patties. Meat Sci. 2010, 84, 613–620. [Google Scholar] [CrossRef] [PubMed]
  28. Aouidi, F.; Okba, A.; Hamdi, M. Valorization of functional properties of extract and powder of olive leaves inraw and cooked minced beef meat. J. Sci. Food Agric. 2017, 97, 3195–3203. [Google Scholar] [CrossRef] [PubMed]
  29. Sanchez de Medina, V.; Priego-Capote, F.; Luque de Castro, M.D. Characterization of Refined Edible Oils Enriched with Phenolic Extracts from Olive Leaves and Pomace. J. Agric. Food Chem. 2012, 60, 5866–5873. [Google Scholar] [CrossRef]
  30. Zribi, A.; Gargouri, B.; Jabeur, H.; Rebai, A.; Abdelhedi, R.; Bouaziz, M. Enrichment of pan-frying refined oils with olive leaf phenolic-rich extract to extend the usage life. Eur. J. Lipid Sci. Technol. 2013, 115, 1443–1453. [Google Scholar] [CrossRef]
  31. Romani, A.; Mulas, S.; Heimler, D. Polyphenols and secoiridoids in raw material (Olea europaea L. leaves) and commercial food supplements. Eur. Food Res. Technol. 2017, 243, 429–435. [Google Scholar] [CrossRef]
  32. Briante, R.; Patumi, M.; Terenziani, S.; Bismuto, E.; Febbraio, F.; Nucci, R. Olea europaea L. leaf extract and derivatives: Antioxidant properties. J. Agric. Food Chem. 2002, 50, 4934–4940. [Google Scholar] [CrossRef]
  33. Atanassova, M.; Christova-Bagdassarian, V. Determination of tannins content by titrimetric method for comparison of different plant species. J. Univ. Chem. Technol. Metall. 2009, 44, 413–415. [Google Scholar]
  34. Yoo, K.M.; Lee, K.W.; Park, J.B.; Lee, H.J.; Hwang, I.K. Variation in major antioxidants and total antioxidant activity of Yuzu (Citrus junos Sieb ex Tanaka) during maturation and between cultivars. J. Agric. Food Chem. 2004, 52, 5907–5913. [Google Scholar] [CrossRef] [PubMed]
  35. Hogan, S.; Zhang, L.; Li, J.; Zoecklein, B.; Zhou, K. Antioxidant properties and bioactive components of Norton (Vitis aestivalis) and Cabernet Franc (Vitis vinifera) wine grapes. LWT-Food Sci. Technol. 2009, 42, 1269–1274. [Google Scholar] [CrossRef]
  36. Lee, S.K.; Mbwambo, Z.; Chung, H.; Luyengi, L.; Gamez, E.; Mehta, R.; Kinghorn, A.; Pezzuto, J. Evaluation of the antioxidant potential of natural products. Comb. Chem. High Throughput Screen. 1998, 1, 35–46. [Google Scholar] [CrossRef] [PubMed]
  37. Abdi, H.; Williams, L.J. Principal component analysis. WIREs Comput. Stat. 2010, 2, 433–459. [Google Scholar] [CrossRef]
  38. Silva, S.; Gomes, L.; Leitao, F.; Coelho, A.V.; Vilas Boas, L. Phenolic compounds and antioxidant activity of Olea europaea L. fruits and leaves. Food Sci. Technol. Int. 2006, 12, 385–396. [Google Scholar] [CrossRef]
  39. Boudhrioua, N.; Bahloul, N.; Slimen, I.B.; Kechaou, N. Comparison on the total phenol contents and the color of fresh and infrared dried olive leaves. Ind. Crops Prod. 2009, 29, 412–419. [Google Scholar] [CrossRef]
  40. Debib, A.; Boukhatem, M.N. Phenolic Content, Antioxidant and Antimicrobial Activities of “Chemlali” Olive Leaf (Olea europaea L.) Extracts. Int. J. Pharmacol. Phytochem. Ethnomed. 2017, 6, 38–46. [Google Scholar] [CrossRef]
  41. Akbaş, U.G.; Uslu, N.; AlJuhaimi, F.; Özcan, M.M.; Ghafoor, K.; Babiker, E.E.; Jamiu, F.G.; Hussain, S. The effect of drying on phenolic compound, antioxidant activity, and mineral contents of leaves of different olive varieties. J. Food Process. Preserv. 2018, 42, e13606. [Google Scholar] [CrossRef]
  42. Žuntar, I.; Putnik, P.; Kovacevic, D.B.; Nutrizio, M.; Šupljika, F.; Poljanec, A.; Dubrovic, I.; Barba, F.J.; Jambrak, A.R. Phenolic and antioxidant analysis of olive leaves extracts (Olea europaea L.) obtained by high voltage electrical discharges (HVED). Foods 2019, 8, 248. [Google Scholar] [CrossRef]
  43. Chinnici, F.; Bendini, A.; Gaiani, A.; Riponi, C. Radical scavenging activities of peels and pulps from cv. Golden Delicious apples as related to their phenolic composition. J. Agric. Food Chem. 2004, 52, 4684–4689. [Google Scholar] [CrossRef]
  44. Benavente-García, O.; Castillo, J.; Lorente, J.; Ortuño, A.; Del Rio, J.A. Antioxidant activity of phenolics extracted from Olea europaea L. Leaves. Food Chem. 2000, 68, 457–462. [Google Scholar] [CrossRef]
  45. Salah, M.B.; Abdelmelek, H.; Abderraba, M. Study of phenolic composition and biological activities assessment of olive leaves from different varieties grown in Tunisia. Medicinal Chem. 2012, 2, 107–111. [Google Scholar]
  46. Rahmaniana, N.; Jafaric, S.M.; Wani, T.A. Bioactive profile, dehydration, extraction and application of the bioactive components of olive leaves. Trends Food Sci. Technol. 2015, 42, 150–172. [Google Scholar] [CrossRef]
  47. Martín-García, B.; Pimentel-Moral, S.; Gómez-Caravaca, A.M.; Arráez-Román, D.; Segura-Carretero, A. Box-Behnken Experimental Design for a Green Extraction Method of Phenolic Compounds from Olive Leaves. Ind. Crops Prod. 2020, 154, 112741. [Google Scholar] [CrossRef]
  48. Goulas, V.; Exarchou, V.; Troganis, A.N.; Psomiadou, E.; Fotsis, T.; Briasoulis, E.; Gerothanassis, I.P. Phytochemicals in olive-leaf extracts and their antiproliferative activity against cancer and endothelial cells. Mol. Nutr. Food Res. 2009, 53, 600–608. [Google Scholar] [CrossRef]
  49. Goulas, V.; Papoti, V.T.; Exarchou, V.; Tsimidou, M.Z.; Gerothanassis, I.P. Contribution of flavonoids to the overall radical scavenging activity of olive (Olea europaea L.) leaf polar extracts. J. Agric. Food Chem. 2010, 58, 3303–3308. [Google Scholar] [CrossRef]
  50. Ranalli, A.; Contento, S.; Lucera, L.; Di Febo, M.; Marchegiani, D.; Di Fonzo, V. Factors affecting the contents of iridoid oleuropein in olive leaves (Olea europaea L.). J. Agric. Food Chem. 2005, 54, 434–440. [Google Scholar] [CrossRef]
  51. Ansari, M.; Kazemipour, M.; Fathi, S. Development of a simple green extraction procedure and HPLC method for determination of oleuropein inolive leaf extract applied to a multi-source comparative study. J. Iran Chem. Soc. 2011, 8, 38–47. [Google Scholar] [CrossRef]
  52. Tayoub, G.; Sulaiman, H.; Hassan, A.H.; Alorfi, M. Determination of oleuropein in leaves and fruits of some Syrian olive varieties. Int. J. Med. Aromatic Plants 2012, 2, 428–433. [Google Scholar]
  53. Bahloul, N.; Kechaou, N.; Mihoubi, N.B. Comparative investigation of minerals, chlorophylls contents, fatty acid composition and thermal profiles of olive leaves (Olea europeae L.) as by-product. Grasas Aceites 2014, 65, e035. [Google Scholar] [CrossRef]
  54. Khanum, F.; Zahoor, T.; Khan, M.I.; Asghar, M. Biochemical profile of olive leaves grown in “Olive Valley” Pakistan. Pakistan J. Sci. Ind. Res. Ser. B Biol. Sci. 2020, 63, 9–16. [Google Scholar] [CrossRef]
Processes 13 02785 g001
Figure 1. Olive leaves used in this study
Figure 1. Olive leaves used in this study
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Processes 13 02785 g002aProcesses 13 02785 g002b
Figure 2. Phenolic chromatograms of olive leaves ((a)—Ayvalık, (b)—Çöpaşı, (c)—Delice (wild olive), (d)—Gemlik, (e)—Sarıulak).
Figure 2. Phenolic chromatograms of olive leaves ((a)—Ayvalık, (b)—Çöpaşı, (c)—Delice (wild olive), (d)—Gemlik, (e)—Sarıulak).
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Figure 3. Biplot graph drawn with results of PCA (Dihyd: 3,4-Dihydroxybenzoic acid).
Figure 3. Biplot graph drawn with results of PCA (Dihyd: 3,4-Dihydroxybenzoic acid).
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Table 1. Moisture contents, bioactive compounds and antioxidant activities of the olive leaves.
Table 1. Moisture contents, bioactive compounds and antioxidant activities of the olive leaves.
VarietyMoisture Content (%)Tannin Content (%)Total Phenolic Content (mg/GAE100 g)Total Flavonoid Content (mg CE/100 g)Antioxidant Activity (mmol TE/kg)
Ayvalık7.03 ± 0.43 *c2.84 ± 0.07 b2164.88 ± 75.22 d16,735.71 ± 160.71 c20.98 ± 0.02 b
Gemlik7.05 ± 0.43 c**2.77 ± 0.14 c2224.40 ± 34.17 c13,800.00 ± 10.71 d20.85 ± 0.05 de
Sarıulak7.67 ± 0.77 b1.73 ± 0.48 e2122.02 ± 9.37 e9010.71 ± 192.86 e21.04 ± 0.03 a
Çöpaşı8.13 ± 0.11 a5.33 ± 0.21 a2338.69 ± 61.81 a18,910.71 ± 107.14 a20.94 ± 0.02 bc
Delice6.92 ± 0.52 d2.42 ± 0.07 d2245.83 ± 49.86 b18,117.86 ± 278.57 b20.88 ± 0.02 d
* standard deviation; ** values within each column followed by different letters are significantly different at p < 0.05.
Table 2. Phenolic compounds from five olive leaf varieties (Ayvalık, Gemlik, Sarıulak, Çöpaşı, Delice (wild olive)).
Table 2. Phenolic compounds from five olive leaf varieties (Ayvalık, Gemlik, Sarıulak, Çöpaşı, Delice (wild olive)).
Phenolic Compounds (mg/100 g;dw)AyvalıkGemlikSarıulakÇöpaşıDelice
Gallic acid84.42 ± 1.10 *C117.51 ± 3.67 A75.39 ± 0.31 D103.16 ± 4.87 B32.06 ± 0.73 E
3,4-Dihydroxybenzoic acid164.37 ± 2.62 C**176.65 ± 2.03 B114.05 ± 3.10 E185.43 ± 0.42 A120.15 ± 2.18 D
Catechin582.59 ± 5.04 A222.59 ± 5.70 E240.12 ± 1.81 D275.32 ± 2.27 C504.76 ± 13.80 B
Caffeic acid50.04 ± 0.96 E75.96 ± 4.36 C51.08 ± 0.35 D79.78 ± 1.73 B142.83 ± 3.19 A
Syringic acid68.64 ± 2.67 B49.95 ± 2.58 D58.12 ± 1.34 C36.81 ± 0.52 E210.96 ± 3.83 A
Rutin149.35 ± 1.08 E245.28 ± 4.78 B155.11 ± 2.44 D221.14 ± 3.26 C418.55 ± 5.41 A
p-Coumaric acid25.32 ± 0.10 D45.71 ± 1.35 B30.26 ± 0.95 C23.28 ± 0.19 E51.45 ± 0.51 A
Ferulic acid50.08 ± 0.20 D52.79 ± 0.13 C55.58 ± 1.31 A53.53 ± 0.49 B42.09 ± 0.82 E
Resveratrol40.20 ± 0.96 A17.19 ± 0.31 E20.12 ± 1.14 CD33.31 ± 1.45 B20.73 ± 0.49 C
Quercetin96.22 ± 3.38 B76.40 ± 2.81 D78.60 ± 0.41 C158.00 ± 1.35 A74.30 ± 1.04 E
Cinnamic acid28.01 ± 0.29 B14.48 ± 0.29 D13.73 ± 0.94 C33.93 ± 1.23 A5.41 ± 0.31 E
Kaempferol24.82 ± 1.44 D14.95 ± 0.26 D8.42 ± 0.27 E18.00 ± 0.06 C28.89 ± 0.11 A
* standard deviation; ** values within each row followed by different letters are significantly different at p< 0.05.
Table 3. Element contents of five olive leaf varieties (Ayvalık, Gemlik, Sarıulak, Çöpaşı, Delice (wild olive); mg/kg;dw).
Table 3. Element contents of five olive leaf varieties (Ayvalık, Gemlik, Sarıulak, Çöpaşı, Delice (wild olive); mg/kg;dw).
Olive VarietiesPKCaMgSNaFeCuMnZnB
Ayvalık1172.99 ± 2.45 *B7114.71 ± 2.20 CD10,763.04 ± 2.62 E1569.66 ± 2.19 B1171.49 ± 3.32 D1325.49 ± 3.99 A45.82 ± 1.10 C6.00 ± 0.58 CD18.59 ± 1.21 D7.11 ± 0.73 D17.60 ± 0.90 D
Gemlik1122.32 ± 26.58 C**7434.46 ± 458.64 B13,400.57 ± 826.22 B1389.39 ± 73.86 E1412.45 ± 27.32 A30.00 ± 6.08 cD45.38 ± 0.70 CD22.62 ± 0.92 A25.37 ± 1.86 B12.31 ± 0.46 A26.86 ± 0.39 A
Sarıulak1276.87 ± 43.78 A7483.67 ± 180.12 A12,225.90 ± 487.84 D1424.06 ± 36.88 D1094.39 ± 48.18 E34.65 ± 1.88 C44.09 ± 8.10 E6.53 ± 0.54 C20.53 ± 0.75 C8.85 ± 0.07 C19.75 ± 0.06 C
Çöpaşı692.84 ± 18.23 D7133.11 ± 36.40 C17,355.70 ± 48.77 A2331.36 ± 11.35 A1362.95 ± 12.85 B34.95 ± 1.58 C89.74 ± 2.28 B18.31 ± 0.58 B27.57 ± 1.63 A6.87 ± 0.03 E24.61 ± 0.91 B
Delice 615.88 ± 9.15 E4311.82 ± 251.05 E13,242.90 ± 460.31 C1469.38 ± 32.31 C1180.18 ± 33.68 C63.98 ± 5.38 B133.82 ± 6.47 A3.94 ± 0.02 E16.85 ± 0.97 E11.71 ± 1.00 B13.85 ± 0.97 E
* standard deviation; ** values within each column followed by different letters are significantly different at p < 0.05.
Table 4. Principal component analysis of phenolic compounds in olive leaves.
Table 4. Principal component analysis of phenolic compounds in olive leaves.
PC1PC2
Eigenvalue6.8133.033
Variability (%)56.77725.273
Cumulative%56.77782.050
Correlation
Gallic−0.838−0.178
Dihyd−0.6140.360
Catechin0.4470.759
Caffeic0.8610.135
Syringic0.9790.172
Rutin0.8820.062
Coumaric0.830−0.369
Ferulic−0.901−0.420
Resveratrol−0.4420.868
Quercetin−0.5820.516
Cinnamic−0.8070.571
Kaempferol0.6090.764
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Aljuhaimi, F.; Ahmed, I.A.M.; Özcan, M.M.; Uslu, N.; Karrar, E. Determination of Antioxidant, Phenolic Compound and Mineral Contents in Olive Leaves by Chromatographic and Spectrophotometric Methods. Processes 2025, 13, 2785. https://doi.org/10.3390/pr13092785

AMA Style

Aljuhaimi F, Ahmed IAM, Özcan MM, Uslu N, Karrar E. Determination of Antioxidant, Phenolic Compound and Mineral Contents in Olive Leaves by Chromatographic and Spectrophotometric Methods. Processes. 2025; 13(9):2785. https://doi.org/10.3390/pr13092785

Chicago/Turabian Style

Aljuhaimi, Fahad, Isam A. Mohamed Ahmed, Mehmet Musa Özcan, Nurhan Uslu, and Emad Karrar. 2025. "Determination of Antioxidant, Phenolic Compound and Mineral Contents in Olive Leaves by Chromatographic and Spectrophotometric Methods" Processes 13, no. 9: 2785. https://doi.org/10.3390/pr13092785

APA Style

Aljuhaimi, F., Ahmed, I. A. M., Özcan, M. M., Uslu, N., & Karrar, E. (2025). Determination of Antioxidant, Phenolic Compound and Mineral Contents in Olive Leaves by Chromatographic and Spectrophotometric Methods. Processes, 13(9), 2785. https://doi.org/10.3390/pr13092785

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