Unveiling the Impact of Drying Methods on Phytochemical Composition and Antioxidant Activity of Anthemis palestina

Different drying techniques may alter the chemical composition of plant extracts and consequently affect their bioactivity potential. The current study was designed to reveal the effect of four different drying methods on the phytochemical composition and antioxidant activity of hydrodistilled essential oil (HD-EO) and methanolic (APM) extract obtained from the aerial part of Anthemis palestina from Jordan. Aerial parts of A. palestina in their fresh (FR) form and after drying in shade (ShD), sun (SD), oven at 40 °C (O40D) and 60 °C (O60D), in addition to microwave (MWD), were used to extract their essential oils by hydrodistillation and to prepare the different methanolic extracts (APM). GC/MS analysis of the different HD-EOs revealed qualitative and quantitative differences among the different samples. While FR, O40D, O60D, and MWD EO samples contained mainly sesquiterpene hydrocarbons (35.43%, 29.04%, 53.69%, and 59.38%, respectively), ShD sample was rich in oxygenated monoterpenes (33.57%), and SD-EO contained mainly oxygenated sesquiterpenes (40.36%). Principal component analysis (PCA) and Cluster analysis (CA) grouped the different drying methods based on their impact on the concentration of chemical constituents. SD-EO demonstrated high DPPH and ABTS antioxidant activity (1.31 ± 0.03) × 10−2; (1.66 ± 0.06) × 10−2 μg/mL, respectively). Furthermore, A. paleistina methanolic extracts (APM) obtained after subjecting the plant to different drying methods showed interesting patterns in terms of their TPC, TFC, antioxidant activity, and phytochemical profiling. Of all extracts, SD-APM extract had the highest TPC (105.37 ± 0.19 mg GA/g DE), highest TFC (305.16 ± 3.93 mg Q/g DE) and demonstrated the highest DPPH and ABTS scavenging activities ((4.42 ± 0.02) × 10−2; (3.87 ± 0.02) × 10−2 mg/mL, respectively); all were supported by correlation studies. LC-MS/MS analysis of the different extracts revealed the richness of the SD-APM extract in phenolic acids and flavonoids.


Introduction
Essential oils (EOs) are complex natural combinations of volatile molecules that are usually extracted from the plant material through hydrodistillation and are well recognized for their wide spectrum of bioactivities.EOs and their constituents have been classified as antioxidants [1][2][3][4][5], food preservatives [6][7][8], and insect repellents [9][10][11] in the past.Exogenous parameters such as soil characteristics, harvest time, plant growth stage, geographical location, extraction technique, and/or drying method were all found to have a significant impact on the extractive yield, chemistry, and related bioactivities [12].Due to the short lifetime of most medicinal herbs, fresh plant material is seldom used for a long time during the year.Herbal remedies are usually collected and then preserved by drying for prolonged use during the whole year.While drying can preserve plant material by preventing enzymatic spoilage, it can alter the yield and chemical composition of EOs and extracts, including constituents like polyphenols, pigments, and vitamins [13].Different drying methods may have pronounced effects on the chemical composition of EOs/extracts [14][15][16], and thus their bioactivity might change.According to the literature, the most common method employed for plant drying is drying in oven [14,[17][18][19][20]. Accordingly, preservation of medicinal plants requires the employment of the optimal drying method to preserve and enhance the content and bioactivity.
The current study was designed to investigate the effect of different drying methods (natural ones (drying in shade (ShD); Sun drying (SD)) and artificial (oven drying at two different temperatures (40 • C: O40D); 60 • C (O60D); microwave drying (MWD))) on the volatile (essential oil) and nonvolatile chemistry of Anthemis palestina, from Jordan.The impact of these different drying methods was assessed in terms of their effect on the chemical constituents, total phenol content (TPC), total flavonoid content (TFC), and antioxidant activity, determined by the DPPH and ABTS methods, in addition to their effect on the methanolic extract composition.

Composition of HDEO Obtained from the Plant Material Subjected to Different Drying Methods
Hydrodistillation of the aerial parts of A. palestina afforded essential oils at varying yields (Figure 1), with the highest yield obtained from the plant material subjected to ShD (0.38%, by weight) and the lowest resulting from microwave (100 W)-dried plant material (0.06% by weight).

GC/MS Analysis of HD-EOs Obtained from A. palestina Aerial Parts Subjected to Different Drying Methods
Each HD-EO obtained from the plant material after being subjected to the selected drying method was analyzed by GC/MS technique to reveal its chemical constituents; the results are listed in Table 1 (Figure S1).The analysis resulted in the identification of 165 constituents with notable qualitative and quantitative variations.In total, 102, 72, 78, 84, 81, and 75 components were identified in the HD-EOs, representing 95.21%, 97.74%, 96.83%, 97.36%, 66.69%, and 99.09% of the total content in FR, ShD, SD, O40D, O60D, and MWD samples, respectively.The identified compounds were grouped into six main groups based on their chemical structures.These were aliphatic compounds (AC), carboxylic acids and esters (CE), monoterpene hydrocarbons (MH), oxygenate monoterpenes (OM), sesquiterpene hydrocarbons (SH), and oxygenate sesquiterpenes (OS).The HD-EO obtained from FR plant sample was dominated by SH and OS, which amounted to 35.43% and 30.82% of the total composition, respectively.Monoterpenes and their oxygenated derivatives made an appreciable contribution to the total composition as well, with the OM being detected at higher concentration levels as compared to MH (16.31%, 7.54%, respectively).The main components detected in this FR-EO sample were γ-muurolene (11.20%), terpinen-4-ol (5.47%), (E)-caryophyllene (3.51%), (E)-β-farnesene (3.20%), sylvestrene (3.19%), and α-zingiberene (3.10%).In the HD-EO obtained from plant samples dried in shade (ShD), OM were the main contributors, amounting to 33.57% of the total composition followed by SH (26.61%).This variation in composition was attributed to the detection of higher concentration levels of terpinen-4-ol (16.94%) as compared to its content in the FR-EO sample.This variation in concentration levels was also observed for γ-muurolene (6.82%), α-zingiberene (5.46%), and (Z)-β-farnesene (5.11%).
In our current study, it was noticed that upon increasing the temperature during the drying process (specifically, oven drying at 40 • C and 60 • C), terpenoidal content varied.Drying at high temperature lowered the total content of monoterpenes but increased the total content of sesquiterpenes.This was in total agreement with the previous work [19,40,41], mainly being attributed to the higher volatility of monoterpenes as compared to sesquiterpenes.

Principal Component Analysis and Cluster Analysis
In the current study, principal component analysis (PCA) and cluster analysis (CA) were applied to the data shown in Table 1, in order to decipher the underlying patterns in the concentrations of the different constituents detected in the oils extracted from A. palestina aerial parts subjected to different drying methods.
The obtained PCA scatter plot, showing the scores of individual chemical components on the primary two principal components (PC1 and PC2) is shown in Figure 2.Each point within this plot corresponds to a distinct chemical component, identified by its KI value as listed in Table 1.The distribution of these points encapsulates their concentration profiles across an array of the different drying techniques employed in the current study including the FR, ShD, SD, O40D, O60D, and MWD methods.The obtained PCA scatter plot, showing the scores of individual chemical components on the primary two principal components (PC1 and PC2) is shown in Figure 2.Each point within this plot corresponds to a distinct chemical component, identified by its KI value as listed in Table 1.The distribution of these points encapsulates their concentration profiles across an array of the different drying techniques employed in the current study including the FR, ShD, SD, O40D, O60D, and MWD methods.Close and careful inspection of this scatter plot revealed an interesting observation related to the emergence of two main clusters that signified chemical components with identical concentration profiles across the different drying techniques.Components located proximally on the plot share analogous profiles, signifying similar responses to the drying methods, while those distantly placed exhibit divergent concentration profiles, implying differential responses to the drying processes.
Components that are prominently positioned on the extremities of the plot, especially along PC1 and PC2 axes, require special attention.The strategic position of these compo- Close and careful inspection of this scatter plot revealed an interesting observation related to the emergence of two main clusters that signified chemical components with identical concentration profiles across the different drying techniques.Components located proximally on the plot share analogous profiles, signifying similar responses to the drying methods, while those distantly placed exhibit divergent concentration profiles, implying differential responses to the drying processes.
Components that are prominently positioned on the extremities of the plot, especially along PC1 and PC2 axes, require special attention.The strategic position of these components underscores their distinct concentration profiles, deviating markedly from the average response.These components, particularly γ-muurolene (1474), terpinen-4-ol (KI 1176), and α-zingiberene (1484), could be significant as potential biomarkers for this genus/species.
To confirm and better understand the obtained results, a dendrogram based on drying methods was established (Figure 3) in which the different drying methods are grouped based on their impact on the concentration of chemical components, revealing a hierarchy of which drying methods resulted in similar chemical profiles.Based on the results shown in this dendrogram, it is clear that the chemical profiles of the HD-EO obtained from the plant material subjected to drying in shade (ShD) and oven drying at 40 • C (O40D) were most similar as compared to other profiles resulting from other drying techniques.The second group of similar chemical profiles corresponded to FR and SD EO-samples.Understanding the effect of drying methods on the EO composition and which could produce similar chemical profiles can be very helpful in taking the correct informative decisions during extraction and preservation processes.
Furthermore, another dendrogram, based on PCA, that focuses on the relationship between individual components was also obtained (Figure 4).Understanding the effect of drying methods on the EO composition and which could produce similar chemical profiles can be very helpful in taking the correct informative decisions during extraction and preservation processes.
Furthermore, another dendrogram, based on PCA, that focuses on the relationship between individual components was also obtained (Figure 4).
The fusion of branches at varying heights indicates the degree of similarity between components, with lower heights indicating greater similarity.Components that merge at shorter distances on the y-axis exhibited similar concentration profiles across drying methods.The farther up the y-axis these merges occur, the more dissimilar the components are.
Joining information obtained from the two dendrograms, one can recognize which drying method is optimal for enhancing or diminishing specific chemical components.If a particular cluster of chemical components (Figure 4) is considered beneficial, the drying method dendrogram (Figure 3) can guide towards the method that maximizes these components.Understanding the effect of drying methods on the EO composition and which could produce similar chemical profiles can be very helpful in taking the correct informative decisions during extraction and preservation processes.
Furthermore, another dendrogram, based on PCA, that focuses on the relationship between individual components was also obtained (Figure 4).1), and the y-axis represents the Euclidean distance, which indicates similarity (the closer the distance is to zero, the more similar the components are) (p value > 0.05).

Antioxidant Activities of HD-EOs
In the present investigation, the antioxidant activities of HD-EOs extracted from the aerial parts of A. palestina subjected to different drying methods were determined and compared to the two positive controls, ascorbic acid and α-tocopherol (Table 2 and Figure S2).The HD-EO obtained from FR plant material had the highest DPPH radical scavenging activity as compared to other HD-EOs (IC 50 : (1.00 ± 0.03) ×10 −2 µg/mL).The EOs obtained from plant material subjected to SD and O40D were comparable ((1.31 ± 0.03) × 10 −2 ; (1.66 ± 0.06) × 10 −2 µg/mL, respectively).These two EOs had also the highest ABTS scavenging activity ((1.34 ± 0.01) × 10 −2 ; (1.91 ± 0.01) × 10 −2 µg/mL, respectively).Results in Table 2 clearly demonstrate the effect of drying method on the antioxidant activity.These findings are in total agreement not only with those listed in the literature [42] but also with the results of statistical analysis performed in our current investigation, that indicated the effect of the different drying methods on the chemical composition.Again, combining the information obtained from dendrograms in Figures 3 and 4 together can offer guidance in choosing the proper drying method that maximizes the beneficial effect (in this case, the antioxidant activity).

Total Phenol Content (TPC), Total Flavonoid Content (TFC) and Antioxidant Activity of APM Extracts
The different A. palestina methanolic extracts (APM) extracts were tested for their TPC and TFC according to the procedure described in the literature [1][2][3]7].The obtained results are listed in Table 2.
As could be deduced from the results obtained in Table 3, APM extract obtained from the SD plant material had the highest TPC (105.37 ± 0.19 mg GA/g DE) and TFC (305.16 ± 3.93 mg Q/g DE).The extract obtained from the plant material subjected to O60D had the lowest TPC and TFC (43.49± 0.57 mg GA/g DE, 52.94 ± 0.90 mg of Q/g DE, respectively).The results demonstrated that extracts obtained from the plants dried at the low temperatures (ShD and SD) had the highest TPC when compared to those obtained at higher temperatures (O40D, O60D, and MWV), thus confirming the effect of drying methods on the composition (especially the phenolics content) [43].The high phenolic content of the extract obtained from MW-dried plant material could be attributed to the effect of microwave radiation and its elevated temperature on the plant tissue, especially the cell wall.This drying method could have enabled the release of cell wall phenolics, and consequently increased their measured content [44].
Most extracts showed moderate to high TFC, except for the extract obtained from the plant dried in the oven at 60 ºC, which had the lowest content (52.94 ± 0.90 mg Q/g DE).
In our study, DPPH and ABTS radical scavenging methods were used to evaluate the antioxidant activity of the different APM extracts; the results are summarized in Table 3 and Figure S3.Most tested extracts had interesting scavenging activities, in the two methods, with the APM-SD extract having the highest DPPH and ABTS methods ((4.42 ± 0.02) × 10 −2 ; (3.87 ± 0.02) × 10 −2 mg/mL, respectively).The observed strong antioxidant activity of this extract could be correlated with its high TPC and TFC.The lowest DPPH and ABTS activities were recorded for APM-O60D (IC 50 of (17.51 ± 1.72) × 10 −2 and (23.99 ± 1.62) × 10 −2 µg/mL, respectively) which was characterized with the lowest TPC and TFC.Our findings strongly support the effect of different drying methods on the observed antioxidant activity of plant extracts [45,46].

Correlation Studies: Antioxidant Activities, TPC, and TFC
In the current study, the obtained data (TPC, TFC, DPPH, and ABTS) were evaluated to calculate the correlation matrix of the different investigated variables (phenolic and flavonoid contents with antioxidant activities).The calculated correlation matrices are displayed in Table 4 (Figures S6 and S7).As could be deduced from the obtained correlation results, there is a very strong correlation (0.99027) between TPC and TFC, suggesting that these two variables are positively related.
The data revealed also strong negative correlations observed between each of TPC and DPPH (−0.95541);TPC and ABTS (−0.95987);TFC and DPPH (−0.95703); and TFC and ABTS (−0.94990).These strong negative correlations indicate an inverse relationship between each pair, confirming the effect of higher phenolic and flavonoid contents on the observed DPPH and ABTS antioxidant activities; as the content increases, IC 50 value decreases, indicating stronger antioxidant activity.There was also a positive correlation observed between the DPPH and ABTS (0.84878).

LC-MS Analysis of Phytochemicals
In the current investigation, the presence of a selected set of constituents in the APM extracts obtained from aerial parts of A. palaestina, dried as described previously, was determined by LC-MS/MS using both the positive and negative ionization modes.The total ion chromatograms (TICs) of the four APM extracts corresponding to the different drying methods employed in the current study are shown in Figure S4; results of the LC-Ms/MS analysis are summarized in Table 5.A total of 43 compounds were detected and identified, including 23 flavonoids, 5 organic acids, 6 phenolic acids, and 10 other compounds.Several compounds were common to all analyzed extracts and were mostly reported to occur in the plants belonging to the same family.The findings of this analysis are in total agreement with those of TPC and TFC, and support the high antioxidant activity observed for the extracts, especially for the APM-SD extract that contained most of the detected compounds, including all phenolic acids and flavonoids.

Plant Material
The aerial parts of A. Palestina were collected from Samou region in Irbid, Jordan, during the full flowering stage (the spring of 2022).The identity of the plant was confirmed using characteristics related to growth habits and morphological attributes in regional floras [24] and was further confirmed by Prof. Dr Jamil Al-Lahham, Department of Biological Sciences-Faculty of Science, Yarmouk University, Irbid, Jordan.A voucher specimen was deposited in the herbarium of the Department of Biological Sciences-Yarmouk University, Irbid, Jordan (YU/09/ AA/1002).

Drying Conditions
Fresh aerial parts of A. Palestina were subjected to different drying methods, immediately after collection.The different drying methods included drying in shade (ShD), sun drying (SD), oven drying at 40 • C (O40D), oven drying at 60 • C (O60D), and microwave drying (MWD).In the ShD method, the aerial parts of the plant (250 g) were dried in a dark dry room with appropriate ventilation until constant weight was achieved (4 weeks, at 25 ± 2 • C).In SD, the aerial parts (250 g) were dried on paper trays under direct sunlight at temperatures ranging between 19 • C and 36 • C for 7 days until constant weight was achieved.In the oven drying (OD) method, the aerial parts of the plant (250 g) were dried in a ventilated oven at two selected temperatures separately, 40 • C and 60 • C, for 3 days to assure constant weight achievement.In MWD (100 W), same amount of aerial plant material was dried for 3 min.

Extraction of Essential Oil
Each dried sample (250 g) was subjected to hydrodistillation for 4 h using a Clevengertype apparatus.The obtained oils were collected, dried over anhydrous MgSO 4, and then stored in sealed amber vials and kept at 4 • C until analysis was performed.

Preparation of the Methanolic Extract
Air-dried (ShD) and grinded aerial parts of A. palestina were subjected to Soxhlet extraction with petroleum ether to get rid of fatty material and waxes.Then, the dried defatted plant residue was extracted in the same apparatus with methanol three times.The combined methanolic extract was evaporated under reduced pressure and the obtained residue (APM) was then assayed for its total phenol content (TPC), total flavonoid content (TFC), and antioxidant activity using DPPH and ABTS assay methods.The extract was then further assayed for its chemical constituents by HPLC-MS/MS analysis.

GC and GC-MS Analysis
A sample of 1 µL of each oil was diluted to 3.0 µL with GC grade n-hexane, and then analyzed by GC-MS (Chromatec Crystal GC-MSD, Yoshkar-Ola, Russia) equipped with a CR-5 MS column (5% diphenyl, 95% dimethyl polysiloxane, 30 m × 0.25 mm, 0.25-µm film thicknesses).In the MS detector, an electron ionization mode of 70 eV was used.The temperature in the MS source was set at 300 • C and transfer line temperature at 230 • C. The temperature column was programmed from 40 • C for 1 min (isothermal) to 280 • C at a constant rate of 3 • C/min, with the lower and upper temperatures being held constant for 3 min.Helium was used as a carrier gas (1.0 mL/min).The relative peak areas were used to calculate the relative percentage concentrations of the detected compounds.A standard solution of C 8 -C 30 n-alkanes mixture was analyzed under the same chromatographic conditions.The chemical constituents of the essential oils were identified by comparing their calculated Kovats retention index (KI) (relative to n-alkanes C 8 -C 30 ), matching their recorded mass spectra with the built-in library spectra and by comparing their mass spectra to those of authentic standards.

Total Phenolic and Total Flavonoid Contents
The total phenolic and total flavonoid contents (TPC, TFC, respectively) of the APM extracts obtained from each drying method were determined by two assay methods, including the Folin-Ciocalteu and aluminum chloride methods, respectively, as previously described [1,2].

Plants 2023 ,
12, x FOR PEER REVIEW 8 of 17 the concentrations of the different constituents detected in the oils extracted from A. palestina aerial parts subjected to different drying methods.

Figure 2 .
Figure 2. PCA loadings plot, based on the first two principal components PC1 and PC2 of the HDEOs constituents (identified by their Kovat Index KI).Each point represents a chemical constituent identified by its Kovats index, detected in the oils obtained from A. palestina subjected to different drying methods (p value > 0.05).

Figure 2 .
Figure 2. PCA loadings plot, based on the first two principal components PC1 and PC2 of the HDEOs constituents (identified by their Kovat Index KI).Each point represents a chemical constituent identified by its Kovats index, detected in the oils obtained from A. palestina subjected to different drying methods (p value > 0.05).

Plants 2023 ,
12,  x FOR PEER REVIEW 9 of 17 most similar as compared to other profiles resulting from other drying techniques.The second group of similar chemical profiles corresponded to FR and SD EO-samples.

Figure 3 .
Figure 3.The dendrogram is based on drying methods, including untreated fresh plant material (p value > 0.05).

Figure 3 .
Figure 3.The dendrogram is based on drying methods, including untreated fresh plant material (p value > 0.05).

Figure 4 .
Figure 4.The dendrogram visualizes the hierarchical clustering of the chemical components based on their PCA results.The x-axis represents the Kovat Index (KI) for each chemical component (as mentioned in Table1), and the y-axis represents the Euclidean distance, which indicates similarity (the closer the distance is to zero, the more similar the components are) (p value > 0.05).

Table 1 .
Chemical compositions of HD-EO obtained from A. palestina aerial parts, subjected to different drying methods, in comparison to the fresh (FR) sample.

Table 2 .
Antioxidant IC 50 values (determined by DPPH and ABTS assay methods) of the HD-EOs obtained from aerial parts of A. palestina subjected to different drying methods.

Table 3 .
TPC, TFC, and antioxidant IC 50 values (determined by DPPH and ABTS assay methods) of the APM extracts obtained from aerial parts of A. palestina subjected to different drying methods.

Table 4 .
Correlation matrix of the variables for the APM extracts of A. palestina (p value > 0.05).

Table 5 .
Major compounds identified in the LC-MS chromatograms of the different APM extracts obtained from A. palaestina subjected to different drying methods.