LC-ESI-QTOF/MS Characterization of Phenolic Compounds in Palm Fruits (Jelly and Fishtail Palm) and Their Potential Antioxidant Activities

Palm fruits have gained growing attention for their nutrition values and health promotion perspectives. They have a diverse range of bioactive compounds including carotenoids, vitamins, dietary fibres and especially polyphenolic compounds. These polyphenolic compounds contribute to the putative health benefits of palm fruits. Nevertheless, the detailed information about these polyphenols in palm fruits is limited. The present work was conducted to comprehensively characterize polyphenols in two palm fruits, jelly palm (Butia ordorata) and fishtail palm (Caryota uren), using liquid chromatography electrospray ionization quadrupole time-of-flight mass spectrometry (LC-ESI-QTOF/MS) and assess their antioxidant potential. The total phenolic content (TPC), total tannins content (TTC), 2,2-diphenyl-1-picrylhydrazyl (DPPH) antioxidant assay and 2,2′-azinobis-(3-ethylbenzo-thiazoline-6-sulfonic acid) (ABTS) scavenging abilities and ferric reducing antioxidant power (FRAP) were higher in the jelly palm fruit while total flavonoid contents (TFC) were higher in the fishtail palm. The LC-ESI-QTOF/MS tentatively identified a total of 86 phenolic compounds in both jelly and fishtail palm fruits. Although both palm fruits exhibited different phenolic profiles, hydroxycinnamic acids and flavonols were the most common in both. In high performance liquid chromatography photodiode array (HPLC-PDA) quantification, 4-hydroxybenzoic acid (317.46 ± 4.68 µg/g) and catechin (4724.00 ± 32.39 µg/g) were the most abundant phenolic acid and flavonoid quantified in the jelly palm fruit, respectively. Quercetin (557.28 ± 7.81 µg/g) and kaempferol 3-O-glucoside (220.99 ± 2.06 µg/g) were the most abundant flavonoids quantified in the fishtail palm. Our study indicates that palm fruit is a good source of polyphenols and has strong antioxidant potential for health promotion. Furthermore, this study provides the scientific basis for an exploitation of jelly and fishtail palm fruits in the food, pharmaceutical and nutraceutical industries.


Introduction
Palm fruits are mostly grown in tropical regions and are rich sources of bioactive compounds such as polyphenols, vitamin E, carotenoids and unsaturated fatty acids [1]. Bioactive compounds extracted from different palm fruits are reported as being effective against various disorders including ageing, cancer, cardiovascular disease, nerve dysfunction, respiratory distress syndrome and diabetes [2]. Thus, the bioactive compound extracts from different palm fruits, especially polyphenols, may contribute to human health.
Jelly palm (Butia ordorata) is a tropical palm species whose fruits and leaves can be processed into different food products [3]. The jelly palm fruit is mainly consumed fresh or used as an ingredient acetonitrile (LiChrosolv, Darmstadt, Germany). The reference standards including protocatechuic acid, catechin, 4-hydroxybenzoic acid, chlorogenic acid, quercetin 3-O-glucoside, kaempferol 3-O-glucoside and quercetin were purchased from Sigma-Aldrich (St. Louis, MO, USA).

Sample Preparation
Samples used for this study were ripened jelly palm (B. ordorata) and fishtail palm (C. uren) fruits, harvested directly from palm trees in Geelong, Victoria, Australia. The fresh palm fruits were collected and weighed for 2-3 kg; jelly palm fruits were blended into a slurry using a 1.5 L blender (Russell Hobbs Classic, model DZ-1613, Melbourne, VIC, Australia) while the fishtail palm fruits were grounded, and the pericarp was collected. Samples were kept at −20 • C for further analysis.

Extraction of Phenolic Compounds
Extracts were prepared by homogenizing with the Ultra-Turrax T25 Homogenizer (IKA, Staufen, Germany) in 30% (v/v) ethanol at 10,000 rpm for 30 s followed by incubation in a ZWYR-240 incubator shaker (Labwit, Ashwood, Vic, Australia) at 120 rpm at 4 • C for 12 h. After incubation, all samples were centrifuged using the Hettich Refrigerated Centrifuge (ROTINA 380R, Tuttlingen, Baden-Württemberg, Germany) at 5000 rpm for 15 min. The supernatant was collected and diluted with ethanol at appropriate ratios for the various antioxidant analysis.

Antioxidant Assays
All the antioxidant assays were performed by adopting the method of Gu et al. [13]. The data was measured by the Multiskan ® Go microplate photometer (Thermo Fisher Scientific, Waltham, MA, USA). All tests were run in triplicate. The standard curves were created with R 2 > 0.995.

Determination of Total Phenolic Content (TPC)
The TPC in palm samples was determined by modifying the method of Severo et al. [14]. In total, 25 µL of 25% (v/v) Folin-Ciocalteu reagent and 200 µL Milli-Q water were added to 25 µL of extracts in triplicates in 96-well plates (Costar, Corning, NY, USA) and incubated for 5 min at room temperature. Then, 25 µL of 10% (w/w) sodium carbonate was added into the reaction mixture and kept in a dark room for 1 h at room temperature. Absorbance was measured at 764 nm in a plate reader. The absorbance was converted to total polyphenol content based on the calibration curve prepared by the gallic acid standard with concentration ranging from 0 to 200 µg/mL. The TPC was expressed as mg of gallic acid equivalents per gram of the sample (mg GAE/g of raw material) on the basis of fresh weight ( fw ).

Determination of Total Flavonoids Content (TFC)
The TFC of palm fruits was evaluated by modifying the aluminium chloride method of Gouveia and Castilho [15]. In total, 80 µL of the diluted sample was mixed with 80 µL of 2% (w/v) aluminium chloride ethanolic solution and 120 µL of 50 mg/mL sodium acetate. Then, the absorbance of the reaction mixture was measured at 440 nm after 1 h incubation in a dark room at room temperature. The values of TFC expressed in quercetin equivalent (µg QE/g fw ) were calculated from the standard curve (quercetin: 0 to 50 µg/mL).

Determination of Total Tannins Content (TTC)
The TTC was estimated by modifying the method of Zou et al. [16]. In total, a 25 µL sample was added in 150 µL of 4% (w/v) methanolic vanillin solution. Then, 25 µL of 32% (v/v) sulfuric acid in methanol was added in the solution mixture and incubated at 25 • C for 15 min. The absorbance was measured at 500 nm and the tannins in samples were quantified by linear regression plotting the absorbance against standard catechin concentration (0-1000 µg/mL). The absorbance was converted to concentration of tannins with the unit of mg of catechin equivalent per gram of sample (mg CE/g).

2,2-Diphenyl-1-picrylhydrazyl (DPPH) Antioxidant Assay
The DPPH free radical scavenging capacity was calculated by modifying the method of Alvarez-Jubete et al. [17]. In total, 260 µL of 0.1 mM of DPPH radical methanol solution was added into 40 µL samples. The absorbance of the reaction mixture was measured at 517 nm after incubating for 30 min. The scavenging activity against DPPH free radicals was expressed as units of ascorbic acid equivalent (mg AAE/g fw ) calculated based on the calibration curve constructed with a standard ascorbic acid solution ranging from 0 to 50 µg/mL.

Ferric Reducing Antioxidant Power (FRAP) Assay
The FRAP method evaluates the capacity of a substance to reduce Fe 3+ in the Fe 3+ -TPTZ complex (ferric-2,4,6-tripyridyl-s-Triazine) into Fe 2+ -TPTZ. The reducing antioxidant power of samples was estimated by modifying the method of Chen et al. [18]. The FRAP reagent was prepared freshly by adding 20 mM FeCl 3 and TPTZ solution (10 mM TPTZ and 40 mM HCl) into 300 mM sodium acetate solution with the volume ratio of 1:1:10. Then, 280 µL of FRAP reagent was mixed with 20 µL of extract. The reaction mixture was incubated at 37 • C for 10 min and absorbance was measured at 593 nm. Concentrations of 0 to 50 µg/mL of ascorbic acid were prepared to construct the standard curve. The results were expressed as mg ascorbic acid equivalents per g of fresh sample weight (mg AAE/g fw ).
2.4.6. 2,2'-Azinobis-(3-ethylbenzo-thiazoline-6-sulfonic acid) (ABTS) Radical Scavenging Assay Free radical scavenging activity was measured by modifying the method of Severo, Tiecher, Chaves, Silva and Rombaldi [14]. The free radical ABTS cations are generated after mixing 7 mM ABTS and 140 mM potassium persulfate (volume ratio: 625:11) followed by incubation in the dark for 16 h. The stock solution was further diluted with ethanol to obtain the ABTS cation solution with an absorbance range of 0.70 ± 0.02 at 734 nm. Then, 290 µL ABTS cation solution was mixed with 10 µL sample. The absorbance was measured at 734 nm after incubation at room temperature for 6 min. The results were expressed as mg ascorbic acid equivalent per gram of sample (mg AAE/g fw ).

LC-ESI-QTOF/MS Characterization of Phenolic Compounds
The LC-ESI-QTOF/MS analysis was carried out by modifying the method of Mateos-Martin et al. [19]. Agilent 1200 series HPLC (Agilent Technologies, Santa Clara, CA, USA) equipped with Agilent 6520 I Accurate-Mass Q-TOF LC/MS (Agilent Technologies, Santa Clara, CA, USA) was used for the identification of polyphenolic compounds. The separation of each compound was carried out using Synergi Hydro-RP 80A LC reverse phase column with an internal diameter of 250 mm × 4.6 nm and particle size of 4 µm (Phenomenex, Lane Cove, NSW, Australia). The column was protected by the Phenomenex C18 ODS guard column with an internal diameter of 4.0 × 2.0 mm. The mobile phase A was acetic acid/water solution (2:98 v/v) and mobile phase B was acetonitrile/water/acetic acid (100:1:99, v/v/v). In total, 6 µL of samples were injected and the separation followed a gradient programme with flow rate of 0.8 mL/min for an 85-min run where the ratio of mobile phase B changed from 10% to 25% in 20 min, from 25% to 35% in 10 min, from 35% to 40% in 10 min, from 40% to 55% in 30 min, from 55% to 80% in 5 min and from 80% to 100% in 2 min followed by maintenance for 2 min. The ratio of mobile phase B was adjusted to 10% from 100% in 3 min after the whole separation process and kept isocratic for 3 min. The samples and column were maintained at 10 • C and room temperature, respectively. The pressure of nitrogen gas condition was set at 45 psi at 300 • C with a flow rate of 5 L/min, while the parameter of sheath gas was set with a flow rate of 11 L/min at 250 • C. The capillary and nozzle voltage were set at 3.5 kV and 500 V, respectively. The complete mass scan was in the range of m/z 50-1300. The control of the process, data collection and identification of phenolic compounds was performed on MassHunter workstation software (Qualitative Analysis, version B.03.01, Agilent). The LC-ESI-QTOF/MS identified compounds with more than 80 library identification scores were further selected for characterization and m/z verification.

HPLC-PDA Analysis
The quantification of targeted phenolic compounds present in palm samples was carried out by Agilent 1200 series HPLC (Agilent Technologies, CA, USA) equipped with a photodiode array (PDA) detector. The same column and conditions were maintained as described above in LC-ESI-QTOF/MS except for sample injection volume of 20 µL. The compositions of extracts were detected under λ 280 nm, 320 nm, and 370 nm by PDA detector. The individual polyphenol was quantified based on linear regression of external standards plotting peak area against concentration. Data acquisition and analysis were performed using Agilent LC-ESI-QTOF/MS MassHunter workstation software (Qualitative Analysis, version B.03.01, Agilent).

Statistics Analysis
All the analyses were performed in triplicate. The values were expressed as mean ± standard deviation (SD). One-way analysis of variance (ANOVA) by Tukey's test was carried out using Minitab ® 18 Statistical software (Minitab Inc., State College, PA, USA) for comparisons of antioxidant activities and the polyphenol contents between samples and p < 0.05 was considered statistically significant.

Polyphenol Estimation (TPC, TFC and TTC)
Jelly and fishtail palm fruits have been reported as good sources of polyphenols [6,20]. The polyphenol contents in ethanolic extracts of jelly and fishtail palm fruits were characterized by TPC, TFC and TTC. The extract of jelly palm fruit was higher in polyphenols (3.74 ± 0.10 mg GAE/g fw ) as compared to fishtail palm (1.75 ± 0.02 mg GAE/g fw ) at p < 0.05 ( Table 1). The TPC of jelly palm in our study was higher than methanolic extracts of the same species (1.71 mg GAE/g fw ) reported by Hoffmann et al. [21], while Krishnamoorthy, Senguttuvan and Krishnaswamy [10] found lower TPC (0.9 mg GAE/g) in the ethanolic extract of fishtail palm. Our total polyphenols content in the jelly palm is comparable to five other genotypes of jelly palms from Brazil (2.65 to 4.02 mg GAE/g) [6]. Jachna et al. [22] also demonstrated that cold storage and pasteurization did not affect the total polyphenolic content in the jelly palm. This might be an advantage for the potential application of jelly palm polyphenols in food, feed and pharmaceutical industries. Table 1. Total phenolic content (TPC), total flavonoid content (TFC) and total tannins content (TTC) and antioxidant activities (2,2-diphenyl-1-picrylhydrazyl (DPPH), ferric reducing antioxidant power (FRAP) and 2,2 -azinobis-(3-ethylbenzo-thiazoline-6-sulfonic acid (ABTS)) of palm fruit samples. The data are shown as mean ± standard deviation (n = 3); a,b indicate the means in a row with significant difference (p < 0.05) using a one-way analysis of variance (ANOVA) and Tukey's test. GAE, gallic acid equivalents; QE, quercetin equivalents; CE, catechin equivalents; AAE, ascorbic acid equivalents.

Antioxidant Assays
Flavonoids are a large class of polyphenols with diverse structures, which have gained a lot of attention due to their potent antioxidant and possible anticancer activities. Some subclasses of flavonoids had been involved in clinical trials [23]. Thus, the flavonoid content is an important index for nutritional assessment in food ingredients. The TFC of jelly palm (63.11 ± 0.51 µg QE/g fw ) was significantly lower as compared to fishtail palm (207.80 ± 4.8µg QE/g fw ) at p < 0.05 (Table 1). Previously, Sujitha and Kripa [20] measured TFC in aqueous and 70% ethanolic extracts of fishtail palm and found higher values than reported in our study. The variation of TFC might be because of the choice of extracts solvents and concentration. Regarding the TTC, the jelly palm had a higher level of TTC (4.06 ± 0.04 mg CE/g) as compared to fishtail palm (1.02 ± 0.01 mg CE/g), as indicated in Table 1. Krishnamoorthy, Senguttuvan and Krishnaswamy [10] reported that the TTC of fishtail palm fruits ranged from 0.5 to 1.6 mg GAE/g. Our study was consistent with some of the previous findings that indicated jelly and fishtail palm fruits are a great source of polyphenols.

Antioxidant Activities (DPPH, FRAP and ABTS)
Different methods are used for determining the antioxidant capacity of food materials. In this study, DPPH, FRAP and ABTS assays were used to quantify the free radical scavenging activity of jelly and fishtail palm fruits. The results of three assays were expressed as mg ascorbic acid/g fw (mg AAE/g fw ). Table 1 shows that the jelly palm exhibits higher DPPH free radical scavenging activity (2.58 mg ± 0.06 AAE/g) as compared to fishtail palm (0.31 ± 0.01 mg AAE/g) at p < 0.05. Sganzerla [24] reported DPPH activity in jelly palm, and found a positive correlation between antioxidant activity and phenolic contents. Fonseca [25] also found DPPH antioxidant activity of jelly palm ranging from 828.27 to 1295.25 mg Trolox equivalent per gram of fruit.
The antioxidant capacity of palm fruits was also determined by the capacity to reduce Fe(III). The FRAP antioxidant activity of jelly palm and fishtail palm was 1.29 ± 0.01 mg AAE/g and 0.03 ± 0.01 µg AAE/g, respectively (p < 0.05). Previously, Denardi, et al. [26] reported higher FRAP activity in another subspecies of jelly palm (Butia eriospatha). Chen et al. [18] also observed higher FRAP activity in freeze-dried proanthocyanidins extracts of another species of fishtail palm (Caryota ochlandra). The ABTS free radical scavenging activity expressed as mg ascorbic acid/g fw was measured by a decolorization assay. Similar to the TPC, DPPH and FRAP assays, jelly palm exhibits higher ABTS (4.38 ± 0.05 mg AAE/g) as compared to fishtail palm (1.85 ± 0.04 mg AAE/g). The ABTS free radical scavenging activity of our jelly palm is comparable to jelly palms (average 4.05 mg Trolox equivalent antioxidant capacity/g) in Brazil [18].
In our study, the estimated antioxidant activity (TPC, DPPH, FRAP and ABTS) in the jelly palm was higher than the fishtail palm. Similarly, Hoffmann, Carvalho, Barbieri, Rombaldi and Chaves [21] reported the correlation between DPPH antioxidant activity and TPC (r 2 = 0.64). Thus, the antioxidant capacity of jelly and fishtail palm fruits can be associated with their polyphenol content. Variations in antioxidant activity in palm fruits can be due to diverse polyphenol ranges in different species, subspecies, genotypes and varieties cultivated at different environments [17]. Also, the type of solvents and extraction methods can impact on polyphenol profile. Boeing et al. [27] found significant differences in polyphenol content, antioxidant activity and amount of particular phenolic compounds in different solvent extracts. In this study, both qualitative and quantitative analyses were carried out to further investigate the presence of actual phenolic components in both jelly and fishtail palm fruits. For the reason, LC-ESI-QTOF/MS and HPLC-PDA were used for identification, characterization and quantification of polyphenols in palm samples. Compounds with a score more than 80 (PCDL score) and mass error <±10 ppm were only selected for characterization and m/z verification purposes. A total of 86 phenolic compounds were reported in jelly and fishtail palm fruits (Tables 2 and 3); they were mainly flavonoids and phenolic acids followed by lignans, stilbenes and other polyphenols. A total of 41 flavonoids and 29 phenolic acids belonging to various polyphenol subclasses were characterized including hydroxycinnamic acids, hydroxybenzoic acids, flavonols, flavones, flavanones, flavanols and anthocyanins, etc. Two palm fruits showed the presence of different polyphenolic compounds, which leads to variation in TPC, TFC, TTC and overall antioxidant activity.

Phenolic Acids
In our study, five different sub-classes of phenolic acids were tentatively characterized in jelly and fishtail palm fruits as shown in Tables 2 and 3, which mainly consist of hydroxycinnamic and hydroxybenzoic acid derivatives. Hydroxyphenylacetic acids, hydroxyphenylpentanoic acids and hydroxyphenylpropanoic acids were also detected in both palm fruits.
Hydroxycinnamic Acid  (Table 2). Sinapine characterized by [M − H] − ion at m/z 309.1568 was proposed for fishtail palm. Previously, chlorogenic acid and aglycones of these compounds (caffeic acid, sinapic acid and ferulic acid) have already been detected in different solvent extracts of jelly palms [3,6,27]. The ferulic acid constituents in fishtail palm fruits have been characterized by LC-MS in the study of Sujitha and Kripa [20]. The presence of caffeic, sinapic and ferulic acid derivatives has already been reported in edible parts of açai and date palm fruits [28][29][30].  (Tables 2 and 3). Hydroxybenzoic acid (m/z 137.0242) and hydroxybenzoic hexose (m/z 299.0070) have already been characterized in jelly palm by Hoffmann, Carvalho, Barbieri, Rombaldi and Chaves [21]. The NaOH hydrolysed sugar date palm fruits also showed the presence of hydroxybenzoic acid derivatives (m/z 253.9) in ethyl acetate extract [31]. Compound 7 in jelly palm fruit and compound 10 in fishtail palm fruit yielding [M − H] − ion at m/z at 315.0731 and 153.0200 respectively, were tentatively identified as protocatechuic acid 4-O-glucoside and protocatechuic acid (Tables 2 and 3). Protocatechuic acid showing m/z 153.2 has already been reported in two açai palm fruits in negative ionization mode [32]. Also, compound 12 in fishtail palm fruit found in positive ionization mode with RT = 42.872 min and [M + H] + at m/z 605.0204 was tentatively identified as gallagic acid (Table 3), a very versatile antioxidant with promising therapeutic and industrial applications potential [33].

Hydroxyphenylacetic, Hydroxyphenylpentanoic and Hydroxyphenylpropanoic Acids
The hydroxyphenylacetic acids and hydroxyphenylpropanoic acids were only characterized in fishtail palm as shown in Table 3 (Table 3). Previously, there was no report demonstrating the detection of hydroxyphenylacetic, hydroxyphenylpentanoic and hydroxyphenylpropanoic acids in both jelly and fishtail palm fruits despite 3,4-dihydroxyphenylacetic acid reported in ethyl acetate extract of date palm fruits after alkaline processing [31].

Flavonoids
Flavonoids are the main class of polyphenols, tentatively identified and characterized by LC-ESI-QTOF/MS in our study. Eight subclasses of flavonoids including flavonols, flavanones, anthocyanins, flavones, isoflavonoids, flavanols, dihydroflavonols and dihydrochalcone were characterized in jelly and fishtail palm fruits as shown in Tables 2 and 3.

Flavonols
Kaempferol glycoside derivatives were tentatively characterized in ethanolic extracts of both jelly and fishtail palm fruits (Tables 2 and 3 (Table 3). These derivatives were also observed in the jelly palm, despite kaempferol 3-O-glucoside (14) tentatively identified by the parent ion at m/z 449.1072 in ESI+ mode (Table 2). Kaempferol 3,7,4'-O-triglucoside and kaempferol 3-O-xylosyl-glucoside showing parent ions at m/z 771.1983 and 581.1472 in ESI and ESI+ modes, respectively were characterized in the jelly palm. Beskow, Hoffmann, Teixeira, Fachinello, Chaves and Rombaldi [6] have indicated the presence of the aglycone kaempferol in ethanolic extract of grounded jelly palm powders. Besides, kaempferol derivatives have been identified in the jelly palm and date palm fruits [21,30]. Some quercetin derivatives were also found in our palm fruits as shown in Tables 2 and 3. Quercetin 3-O-glucoside (15), quercetin 3-O-rutinoside (16), and quercetin (17) exhibiting precursor ion at m/z 465.1008, 611.1579 and 303.0486 in positive ionization mode were proposed for jelly palm fruit ( Table 2). These compounds were also tentatively characterized in fishtail palm fruits despite quercetin 3-O-glucoside (RT = 37.133 min) giving precursor ion at m/z 463.0878 in ESI− mode (Table 3). Compound 28 with [M + H] + at m/z 551.1008 in fishtail palm fruit was characterized as quercetin 3-O-(6"-malonyl-glucoside). The detection of aglycone quercetin in the jelly palm was reported previously [3,6,27]. In addition, it was proven that jelly palm presents constituents of quercetin glucosides derivatives and quercetin 3-O-rutinoside [3,26]. Quercetin 3-O-rutinoside has been found in leaves of fishtail palm by LC-MS analysis in the study of Sujitha and Kripa [20]. Moreover, the quercetin derivative constituents in date palm fruits were also investigated by chromatography analysis [30,34].  (Table 3). Farag, Mohsen, Heinke and Wessjohann [28] also discovered the chrysoeriol compound conjugated with hexoside in the skin of date palms using LC-ESI-QTOF/MS. Compound 22 in jelly palm presenting a molecular ion at m/z 607.1674 in ESI mode was tentatively characterized as neodiosmin ( Table 2). Previously, two compounds of procyanidin dimers with m/z 577.1 were detected in Euterpe oleracea açai fruits in negative ionization mode [32].

Anthocyanins, Isoflavonoids, Dihydroflavonols and Dihydrochalcones
The anthocyanins constituents were tentatively identified only in negative ionization mode as shown in Tables 2 and 3 In fishtail palm fruit, compound 40 exhibiting precursor ion at m/z 520.1225 was proposed as petunidin 3-O-(6"-acetyl-glucoside). Previously, two cyanidin derivative anthocyanins were characterized in jelly palm fruit [6]. In the study of Pacheco-Palencia, Duncan and Talcott [32], cyanidin derivatives, peonidin derivatives and pelargonidin derivatives were proposed as anthocyanins compounds in açai fruits.
Isoflavonoid constituents were also found in both jelly and fishtail palms as shown in Tables 2 and 3

Other Polyphenols
The LC-ESI-QTOF/MS detected 12 compounds belonging to seven different subclasses of other polyphenols in jelly and fishtail palm fruits (Tables 2 and 3). Most of these compounds were first reported in jelly and fishtail palm fruits. We divided compounds of other polyphenols into two subgroups: tyrosols and others.

Tyrosols
A total of four compounds with a hydroxytryrosol structure were proposed for both jelly and fishtail palm fruits in negative ionization mode (Tables 2 and 3 (Tables 2 and 3). Previously, the presence of hydroxycoumarins compounds (umbelliferone derivatives) was reported in fishtail palm fruits [20]. Patel et al. [36] indicated the possible presence of thymol in the leaf of fishtail palm after chromatography and spectroscopic analysis. The concentrated methanolic extract of immature fishtail palm fruits highlighted the pyrogallol 1,3-dimethyl ether constituents [9].
The screening and characterization of polyphenolic compounds showed that some of the polyphenols presented in two palm fruits have strong antioxidant potential. Hydroxycinnamic acid derivatives, hydroxybenzoic acids and their derivatives, protocatechuic acid, chlorogenic acid, catechin, matairesinol, hydroxytyrosol, quercetin and kaempferol derivatives are regarded as potential compounds showing considerable free radical scavenging capacity [37][38][39]. The presence of these antioxidant compounds indicates that both jelly and fishtail palm fruits can be good sources of polyphenols and antioxidant potential.

Quantitative Analysis of Phenolic Compounds by HPLC-PDA
Seven polyphenols were targeted to quantify through HPLC-PDA including three phenolic acids (chlorogenic acid, protocatechuic acid and 4-hydroxybenzoic acid) and four flavonoids (quercetin 3-O-glucoside, catechin, quercetin and kaempferol 3-O-glucoside) based on the LC-ESI-QTOF/MS characterization and previously reported antioxidant activities. The quantification of individual polyphenols was computed considering the UV-Vis absorption and calibration curves of external standards.
The polyphenols quantified through HPLC-PDA in the jelly palm were higher than in fishtail palm. These HPLC results support our TPC values determined using the Folin-Ciocalteu method. Among the three selected phenolic acids, chlorogenic acid was the only phenolic acid detected in both palm fruits ( Table 4). The concentration of chlorogenic acid in the jelly palm (290.10 ± 3.98 µg/g fw ) was higher than fishtail palm fruit (140.23 ± 1.78 µg/g fw ). Boeing et al. [27] already reported the chlorogenic acid content in another jelly palm species. Moreover, 4-hydroxybenzoic acid (RT = 25.337 min, 317.46 ± 4.68 µg/g fw ) was only detected in jelly palm fruit, while protocatechuic acid (RT = 6.929 min, 68.46 ± 0.97 µg/g fw ) was only found in fishtail palm. Beskow, Hoffmann, Teixeira, Fachinello, Chaves and Rombaldi [6] also quantified hydroxybenzoic acid content with an average value of 123.39 mg/100g in five different genotypes of jelly palm using HPLC. Flavonols were found to be higher in fishtail palm fruit as compared to jelly palm fruits. Quercetin was the major compound in this group, with a concentration of 360.19 ± 4.53 µg/g fw in jelly palm and 557.28 ± 7.81 µg/g fw in fishtail palm fruit. Beskow, Hoffmann, Teixeira, Fachinello, Chaves and Rombaldi [6] already reported higher quercetin contents in Berzelian jelly palm. Quercetin 3-O-glucoside and kaempferol 3-O-glucoside were also present in both palm fruits. The quercetin and kaempferol 3-O-glucoside content might account for the higher TFC value in fishtail palm fruit as compared to jelly palm. In our results, we found that catechin was high in jelly palm fruit (4.72 ± 0.03 mg/g fw ), which might be involved in higher antioxidant activity.

Conclusions
It has been established in this work that LC-ESI-QTOF/MS is an effective and powerful analytical tool to characterize most of the polyphenols present in jelly and fishtail palm fruits. The TPC, TTC, DPPH, FRAP and ABTS scavenging activity was higher in jelly palm compared to fishtail palm. LC-ESI-QTOF/MS characterizes a total of 42 and 60 phenolic compounds in jelly and fishtail palm fruits, respectively. Hydroxycinnamic acids and flavonols were the most common polyphenols reported in both palm fruits. The HPLC-PDA enabled the quantification of some targeted phenolic compounds and found that catechin and quercetin were the most abundant polyphenols in jelly and fishtail palm, respectively. In short, both palm fruits are a good source of polyphenols and could be utilized in food, feed and pharmaceutical industries.