Antioxidant and phytometabolite profiles of ethanolic extract from the cascara pulp of Coffea arabica collected from Gayo Highland: A study for potential anti-photoaging agent

Background: As the most abundant coffee by-product, cascara pulp has been considered a good source of antioxidants which could be used to prevent photoaging. The aim of this study was to determine the phytometabolite profiles, antioxidant and photoaging properties of the ethanolic extract of Coffea arabica cascara pulp. Methods: Ethanolic maceration was performed on the fine powder of C. arabica cascara pulp collected from Gayo Highland, Aceh Province, Indonesia. The filtrate obtained was evaluated for its 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activity, total phenolic content (TPC), and total flavonoid content (TFC). The phytometabolite profiling was conducted qualitatively using reagents and quantitatively using gas chromatography—mass spectroscopy (GC-MS). The potential of the cascara pulp phytometabolites in inhibiting activator protein-1 (AP-1) was evaluated through molecular docking. Results: The extract had TPC and TFC of 2.04 mg gallic acid equivalent/g extract and 91.81 mg quercetin equivalent/g extract, respectively. The half-maximal inhibitory concentration (IC 50) for the DPPH inhibition reached as low as 9.59 mg/L. Qualitative phytocompound screening revealed the presence of alkaloids, saponins, tannins, flavonoids, steroids, quinones, polyphenols, and triterpenoids. GC-MS revealed the extract containing 5-hydroxy-methylfurfural (22.31%); 2,5-dimethyl-4-hydroxy-3(2H)-furanone (0.74%); and caffeine (21.07%), which could form interaction with AP-1 with binding energies of -172.8, -150.8, and -63.188 kJ/mol, respectively. Conclusion: Ethanolic extract from C. arabica cascara pulp potentially have anti-photoaging properties which is worthy for further investigations in the future.


Introduction
Aging, a process that manifests in excessive wrinkle, cutis laxa, degraded collagen and hyperpigmentation, occurs naturally.Other than endogenous factors, the process could be accelerated by exogenous factors. 1 Exogenous aging is caused by the surrounding environment that could enhance the oxidative stress in skin tissue including but not limited to cigarette smoke, air pollution, and UV exposure. 1,2The chronic exposure of solar radiation could also contribute to the development of skin cancer. 3As an addition, maintaining youthful appearance has been the goal of many individual recently which create multibillion-dollar industry of anti-aging products. 4 radiation from the sun contains three spectra components including UV-A (320-400 nm), UV-B (280-320 nm), and UV-C (100-280 nm). 5 UV rays from the sun are known to accelerate the aging process of the skin by inducing oxidative stress that inhibits collagen synthesis.6 Photoaging occurs at the molecular level by UV-induced matrix metalloproteinases (MMPs), which degrade skin collagen.UV stimulates growth factor and cytokine receptors on keratinocytes and fibroblasts, resulting afterward activates mitogen-activated protein (MAP) kinase pathways, leading to downstream signal transduction for the pathophysiology of photoaging in human skin.7 An increase in transcription factors including activator protein-1 (AP-1) and nuclear factor kappa B (NF-κB) is also produced according to the effects of oxidative stress.Gene regulation in response to cell proliferation and differentiation depends on regulation by the transcription factor AP-1. [8][9][10] Clinical indications of photoaging are based on age, gender, particularly skin, and ethnic and the clinical signs include wrinkles, sagging, roughness, and telangiectasia.][6][7][8][9][10][11][12][13][14] Therefore, searching for anti-photoaging has been a crucial research topic in the field of dermatology.
Natural products have been studied for their ability in providing photoprotection, hence preventing photoaging. 4,15These natural products usually have high antioxidant activities which could suppress the excessive UV radiation-induced reactive oxygen species (ROS) generation. 16Coffea arabica and its by-products have been reported multiple times containing abundant antioxidants. 17,180][21] Previously, cascara pulp has been extracted using water, methanol, or even supercritical CO 2 . 22,23However, the use of ethanol solvent that could attract polar compounds and several non-polar compounds is scarcely reported. 24The present study tried to close the gap by determining the phytometabolite profile of the ethanolic extract of C. arabica cascara pulp along with its antioxidant properties.Furthermore, the potential of the cascara pulp extract as photoaging agent has been evaluated in-silico.

Materials
Materials used in this study included methanol, ethanol 96%, ascorbic acid, gallic acid, quercetin, potassium acetate, and sodium carbonate.Reagents for phytochemical screening included AlCl 3 powder, Mg powder, Liebermann-Burchard reagent, Folin-Ciocalteu reagent, Mayer reagent, Dragendorf reagent, and Wagner reagent.All materials and reagents were analytical grade and procured from Merck, Selangor, Malaysia.Other reagents were procured from specific companies as described in each section.

Extraction of cascara pulp
The cascara of C. arabica was collected from Gayo Highland, Aceh Province, Indonesia.Cascara pulp was crushed into small pieces to produce simplicia powder and air-dried.The maceration was performed on the dried simplicia powder using ethanol 96% (Merck, Selangor, Malaysia) with ratio of 1:10 for 7 days.Thereafter, the filtrate was collected and dried in a rotary evaporator (45°C) (N-1300VW, EYELA, Tokyo, Japan).

REVISED Amendments from Version 1
In this new version, we have revised our title from "photoaging agent" to "anti-photoaging agent".We have replaced all "hidroxy" to "hydroxy" in the entire article.We added more information about photoaging in Introduction section and we added the references for both methods of DPPH inhibition assay and total phenolic (TPC).In addition, we also have revised all the names of the compounds according to IUPAC.
Any further responses from the reviewers can be found at the end of the article extract was dissolved up to 10 mL using ethanol 96% to produce 100 mg/L extract solution, which was further dissolved into 2-10 mg/L.DPPH solution was prepared by adding its powder (7.9 mg) into 50 mL methanol (Merck, Selangor, Malaysia).One mL of DPPH 0.4 mM was added into priorly-dissolved extract, homogenized, and incubated at 37°C for 30 minutes.The absorbance was measured at 517 nm on UV-Vis spectrophotometer (Uvmini-1250, Shimadzu, Kyoto, Japan).Ascorbic acid (Merck, Selangor, Malaysia) was used as the control.
Determination of total phenolic (TPC) and flavonoid contents (TFC) The total phenolic (TPC) was determined using Folin-Ciocalteu method as described previously. 26,27Briefly, the cascara pulp extract (0.2 mL) was added into 15.8 mL distilled water which had been pre-added with 1 mL Folin-Ciocalteu reagent (Merck, Selangor, Malaysia).The mixture was shaken rigorously and rested for 8 minutes before added with 15 mL sodium carbonate 10% (Merck, Selangor, Malaysia) and subsequently incubated at room temperature for 2 h.The absorbance was measured at 765 nm using an UV-Vis spectrophotometer (Uvmini-1250, Shimadzu, Kyoto, Japan).The value in concentration was obtained from the calibration curve constructed using gallic acid (gallic acid equivalent (GAE)/g extract) and assigned as total phenolic content (TPC).Gallic acid was purchased from Merck, Selangor, Malaysia.
The total flavonoid content (TFC) was determined using a method as described previously, 15 its value was derived from absorbance at 450 nm of a mixture consisting of potassium acetate (0.2 mL) (Merck, Selangor, Malaysia), AlCl 3 (0.2 mL), and distilled water (5.6 mL) which was incubated for 30 minutes at room temperature (all from Merck, Selangor, Malaysia).TFC was calculated through a calibration curve based on quercetin concentrations (quercetin equivalent (QE)/g extract).Both TPC and TFC measurements followed the procedure reported previously. 26alitative phytochemical screening Phytochemical screenings followed the procedure reported previously. 28,29Flavonoids were detected from a reaction between the cascara pulp extract (0.5 in 10 mL methanol) and Mg powder (0.5 mg) in the presence of HCl 0.5 M. As for saponin contents, the extract (0.5) was shaken to form a stable foam after dissolved in 10 mL boiling water.Three reagents, namely Mayer, Dragendorf, and Wagner (all from Merck, Selangor, Malaysia), were used to identify alkaloid contents.Tannins were identified by reacting the extract (0.5 g in 10 mL distilled water) with FeCl 3 10%.Quinones was observed through the appearance of red color following the drop-wising of sulfuric acid (1-2 drops) into the extract (0.5 g in 10 mL methanol).As for the steroids and triterpenoids, their presence was indicated by color change following the a few drops addition of reagent Liebermann-Burchard (Merck, Selangor, Malaysia) to the cascara pulp extract (1 g in 10 mL n-hexane).

Gas chromatography-mass spectroscopy (GC-MS) analysis
The cascara pulp extract was analyzed for its phytometabolites based on gas chromatography-mass spectrometry (GC-MS) (Shimadzu QP2010, Kyoto, Japan).The analysis was carried out with column temperature of 40°C (10°C/ minute), flown with He gas.The retention was made 3 minutes (30°C/minute) until the temperature reached 299°C with total running time of 29.63 minutes through splitless injector (280°C; 4.34 psi) with total current of 8.4 mL/m in a 30 m-long Rti-1MS column.Data from mass spectrometer was compared with the database from National Institute of Standards and Technology (NIST).

Antioxidant properties
Antioxidant properties of C. arabica cascara pulp were investigated based on the TPC, TFC, and DPPH assay.The TPC and TFC values of the cascara pulp extract were presented in Table 1.The calibration curves obtained from the measurement of gallic acid and quercetin had R 2 values of 0.9284 and 0.9868, respectively.When the extract was reacted with Folin-Ciocalteu reagent, the UV-Vis absorbance at 765 nm was found to be 0.055 a.u.Meanwhile, the absorbance of 1.545 a.u. was obtained following the reaction between the reaction with AlCl 3 and CH 3 COOK.The foregoing absorbance gave the TPC and TFC of the cascara pulp extract as much as 2.04 mg GAE/g extract and 91.81 mg QE/g extract, respectively.DPPH inhibition percentages yielded by the extract with concentrations ranged from 2 to 10 mg/L have been presented (Figure 1).When the extract concentrations were at 2, 4, 6, 8, and 10 mg/L, the DPPH inhibition percentages reached 25, 29.41, 33.82, 42.65, and 54.41%, respectively.Based on these values, the linear equation with a slope and intercept of 3.603 and 15.44, respectively (R 2 = 0.933).As for the ascorbic acid (control), at the same concentration range, the DPPH inhibitions were 41.18-60.29%.The IC 50 value of the cascara pulp extract in scavenging free radicals DPPH was 9.59 mg/L, which could be considered highly active as an antioxidant.However, the value still fell short by almost 2-fold when compared with the ascorbic acid (5 mg/L).

Qualitative phytometabolite screening
Results of the qualitative phytometabolites screening of C. arabica cascara pulp have been presented in Table 2. Positive results were indicated by the Dragendorf and Wagner tests, though the phytometabolites were not sensitive to Mayer test.Members of saponin, steroid, quinone, and tannin families were also found positive in the extract.Flavonoids and polyphenols, widely known antioxidant compounds, were shown to be contained in the extract.The presence of triterpenoids was not observable by the qualitative screening.

Phytometabolite profile based on GC-MS
After the initial screening, GC-MS analysis was carried out to identify the phytoconstituents in the extract.The chromatogram depicting peaks from each phytometabolite detected has been presented in Figure 2. Details of the recorded compounds along with the quantitative information (peak area which could be associated to the metabolite contents) have been presented in Table 3.As many as 30 phytocompounds were identified in this present study.Compounds 5-hydroximethylfurfural; caffeine; n-hexadecanoic acid; cis-vaccenic acid; and 2(1H)-naphthalenone, 3,5,6,7,8,8a-hexahydro-4, 8a-dimethyl-6-(1-methylethenyl) topped the phytometabolite abundance rank in the extract with peak areas of 22.31, 21.07, 12.85, 11.94, and 5.26%, respectively.1][32] The aforementioned phytocompounds were then selected for molecular docking study against AP-1.In-silico interactions between the identified phytometabolites and AP-1 The summaries of molecular docking results were presented in Table 4. Highest binding energy was exhibited by 5-hydroxy-methylfurfural (-172.8kJ/mol) attributed to six hydrogen bonds and five Van der Waals interactions.The second most potential AP-1 inhibitor was 2,5-dimethyl-4-hydroxy-3(2H)-furanone with a binding energy of -150.8 kJ/mol involving four H bonds and three non-polar interactions.Caffeine appeared to have the lowest affinity with AP-1, where the binding energy only reached -63.188 kJ/mol despite the seven H bond, six alkyl, and four pi-alkyl interactions.

Discussion
In this present study, the antioxidant activity of C. arabica cascara pulp could be considered high since the IC 50 value of DPPH inhibition reached below 100 mg/L. 26The antioxidant properties of the cascara pulp extract are further supported by the TPC and TFC of 2.04 mg GAE/g extract and 91.81 mg QE/g extract, respectively.C. arabica has previously been reported to possess high antioxidant activities.A study in India revealed that 200 mg/L C. arabica seed extract could yield >90% DPPH inhibition. 18The authors attributed the finding with the donation of hydrogen from hydroxyl groups of the bioactive metabolites which could stop the oxidation process by DPPH via stable end products formation. 18Other studies also observed the strong antioxidant activity of C. arabica along with its high TPC. 33,34In our previous systematic review, we found there are at least 13 studies confirming the antioxidant activities of C. arabica by-products. 17IC 50 value obtained from the DPPH assays of arabica coffee husk using supercritical fluid extraction was >0.25 mg/L. 23Arabica coffee pulp extracted with distilled water was reported to contained TPC as high as 0.28 mg GAE/g extract. 35Hence, our ethanolic extract from C. arabica cascara pulp had higher DPPH scavenging activity and TPC value than that of previously studied by-products.
UV radiation could induce aging process (photoaging) by promoting reactive oxygen species (ROS) production which could result in excessive oxidative stress and inflammation in skin.Indeed, ROS is naturally produced in mitochondria resulted from the aerobic metabolism, particularly in electron transport chain, which contributes to slow endogenous aging. 36However, there are studies who suggest that ROS production could be enhanced by UV light exposure.Activities of keratinocytes and fibroblasts in producing ROS are positively correlated with the UV radiation intensity. 37,38he increase of ROS release following the solar light exposure could also attributed to the downregulation of ROS neutralizing enzymes viz glutathione reductase and peroxidase. 1 In addition, ROS could mediate several signaling pathways to induce skin damage. 16,37,39A terpenoid isolated from an ethyl acetate fraction of coffee silverskin was reported to be capable of inhibiting ROS production and potential as photoaging agent. 22Taken altogether, the cascara pulp obtained herein is potential in preventing photoaging attributed to its high antioxidant activity that could suppress the oxidative stress in skin tissue following solar radiation.
ROS induced from the UV exposure could initiate the cascading reaction of mitogen-activated protein kinases (MAPKs), consisting of extracellular C-Jun N-terminal kinase (JNKs), signal-regulated kinase (ERK), and p38MAPK. 40The activation of JNK and p38MAPK pathways promotes activator protein-1 (AP-1) and cyclooxygenase-2 (COX-2). 40This reaction cascade contributes to the enhanced levels of interleukin (IL)-8, IL-10, prostaglandin G2, and vascular endothelial factor which are responsible for inflammatory reaction, differentiation, immunosuppression, proliferation, as well as angiogenesis. 1Moreover, AP-1 is responsible to aging process by both inhibiting collagen synthesis via direct binding with procollagen promoter and degrading collagen via interaction with matrix metalloproteinase 1 (MMP1). 41,424][45] Hence, we had performed molecular docking studies to observe the potential of the phytometabolites from the cascara pulp extract to interact with AP-1.
In this present study, two predominant compounds (5-hydroxy-methylfurfural and caffeine) and one minor compound (2,5-dimethyl-4-hydroxy-3(2H)-furanone) were shown to have strong affinity with AP-1 through molecular docking studies.From the highest to the lowest, the phytometabolites could be ranked as follows: 5-hydroxy-methylfurfural > 2,5dimethyl-4-hydroxy-3(2H)-furanone > caffeine.Both 5-hydroxy-methylfurfural and 2,5-dimethyl-4-hydroxy-3(2H)furanone are common food additives, while caffeine is a common compound in coffee products.Similarly, a study found that caffeine was among the isolates obtained from antioxidant assay-guided procedure on Robusta coffee seeds, yet its bioactivity is relatively minimum. 46In our previous in-silico screening using gallic acid, malonic acid, gallic acid, and decanoic acid from water:ethanol combination extract of C. arabia cascara pulp, ARG173, ARG176, ARG177, and LYS289 were also found as common binding sites. 47The highest binding energy found in that previous study was -242.24kJ/mol. 47Though the highest binding energy in this present study is -172.8kJ/mol, obtained from 5-hydroxy-methylfurfural, the value is relatively high and could be considered as an effective binding. 48,49Moreover, the antioxidant properties of the cascara pulp herein could contribute to other preventive mechanisms of photoaging.Nonetheless, it is worth noting that in-silico study alone is not sufficient to conclude the AP-1 inhibition by the cascara pulp extract, where in vitro study is a must. 24

Conclusions
The ethanolic extract from the cascara pulp of C. arabica is highly active as an antioxidant agent.Phytocompound profiling evidences the antioxidant metabolite richness of the cascara pulp extract which could act as anti-photoaging agent.In-silico studies reveal the potential of strong interaction between the bioactive phytometabolites with AP-1.Further research with in vitro or in vivo design is warranted to confirm the anti-photoaging activities of the phytometabolites contained in the C. arabica cascara.The manuscript "Antioxidant and phytometabolite profiles of ethanolic extract from the cascara pulp of Coffea arabica collected from Gayo Highland: A study for potential photoaging agent" with authors Wahyu Lest, Kartini Hasballah, M. Yulianto Listiawan, Sofia Sofia is interesting and original.I think it would be of interest not only to readers of F1000Research but also to other researchers.I think that the task that the authors have set themselves is very serious.

Data availability
In the Introduction part, the authors have cited 10 sources from the last 3-5 years, out of a total of 14.This shows that the authors have worked very seriously on their goal to prove the seriousness of the research they have done.I would like to say that I think the Introduction is too short and I ask the authors to add more sources.
As for the Methods and Materials section, the methods are generally known, well described, and could be replicated by any researcher.It struck me that two of the methods have no sources noted.I ask the authors to cite where they got the methods because according to the journal's requirements, this omission amounts to plagiarism.These are the methods: DPPH inhibition assay; Determination of total phenolic (TPC).The authors may have modified them in their use but they should also note this.
Results are presented accurately and clearly.They are supported by relevant tables and figures.Accordingly, the results obtained by the authors enable any reader of this manuscript to get a clear idea.In my opinion, the authors should note Total Phenolics and Total Flavonoids in the table.The phenols and flavonoids for which the authors present the results are not one specific compound and for that they use the corresponding equivalent.For example, if the authors had used another equivalent such as catechin or rutin to prove the flavonoids, I think they would have obtained different results.Another thing that I would like the authors to pay attention to is the formula of potassium acetate CH 3 CO 2 K, in my opinion, it should be written according to IUPAC CH 3 COOK.I also ask the authors to write the formulas of the compounds in the text according to the IUPAC requirements, for example: 2,5-Dimethyl-4-hydroxy-3(2H)-furanone.
In the Discussion section, I think the authors presented their results accurately and clearly and supported them with relevant citations.In my opinion, the conclusion supports the results obtained by the authors.

Is the work clearly and accurately presented and does it cite the current literature? Partly
Is the study design appropriate and is the work technically sound?Yes

Are sufficient details of methods and analysis provided to allow replication by others? Yes
If applicable, is the statistical analysis and its interpretation appropriate?I cannot comment.A qualified statistician is required.
Are all the source data underlying the results available to ensure full reproducibility?Yes

Are the conclusions drawn adequately supported by the results? Yes
Competing Interests: No competing interests were disclosed.
Reviewer Expertise: My research area is Total Phenols and Total Flavonoids, Bioactive Compounds and Antioxidant Activity of Extracts from Different Natural Plants I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard, however I have significant reservations, as outlined above.

Figure 3 .
Figure 3. 3D (left and middle) and 2D (right) conformations of the interactions between the phytometabolites and AP-1.

Table 1 .
Antioxidant capacity of the ethanolic extract from the cascara pulp based on total phenolic content and total flavonoid content.

Table 2 .
Qualitative screening results of the phytometabolites contained in the extract.
(-) and (+) indicate the presence and absence of the phytometabolites, respectively.

Table 3 .
Phytometabolites of the ethanolic extract as identified by the GC-MS.

Table 4 .
Molecular docking results of the interaction between the phytometabolites and AP-1.

Table 4 .
Continued 3D (left and middle) and 2D (right) conformations of the interactions between the phytometabolites and AP-1.jpg Data are available under the terms of the Creative Commons Attribution 4.0 International license (CC-BY 4.0).