Elucidation of Antioxidant Compounds in Moroccan Chamaerops humilis L. Fruits by GC–MS and HPLC–MS Techniques

The aim of this study was to characterize the phytochemical content as well as the antioxidant ability of the Moroccan species Chamaerops humilis L. Besides crude ethanolic extract, two extracts obtained by sonication using two solvents with increased polarity, namely ethyl acetate (EtOAc) and methanol-water (MeOH-H2O) 80:20 (v/v), were investigated by both spectroscopy and chromatography methods. Between the two extracts, the MeOH-H2O one showed the highest total polyphenolic content equal to 32.7 ± 0.1 mg GAE/g DM with respect to the EtOAc extract (3.6 ± 0.5 mg GAE/g DM). Concerning the antioxidant activity of the two extracts, the EtOAc one yielded the highest value (1.9 ± 0.1 mg/mL) with respect to MeOH-H2O (0.4 ± 0.1 mg/mL). The C. humilis n-hexane fraction, analyzed by GC–MS, exhibited 69 compounds belonging to different chemical classes, with n-Hexadecanoic acid as a major compound (21.75%), whereas the polyphenolic profile, elucidated by HPLC–PDA/MS, led to the identification of a total of sixteen and thirteen different compounds in both EtOAc (major component: ferulic acid: 104.7 ± 2.52 µg/g) and MeOH-H2O extracts (major component: chlorogenic acid: 45.4 ± 1.59 µg/g), respectively. The attained results clearly highlight the potential of C. humilis as an important source of bioactive components, making it a valuable candidate to be advantageously added to the daily diet. Furthermore, this study provides the scientific basis for the exploitation of the Doum in the food, pharmaceutical and nutraceutical industries.

Such a species is cultivated in many Mediterranean countries as an ornament, considering its robustness and decorative features.
Some components of this plant have been used as food as an important source of nutritional energy [3], or in traditional medicine. The husks are eaten in Southern Spain, the fruits in Morocco and the young suckers in Italy. Leaf extracts of Chamaerops humilis L. (C. humilis) have been commonly used for the treatment of diabetes, digestive disorders, spasms, tone and gastrointestinal disorders [4,5]. Moreover, their fruits have astringent properties thanks to their tannin content, even though, in Morocco, they have been rarely consumed due to their bitter taste [4].
Other studies have shown the beneficial effects of these fruits against hyperlipidemia in an animal model of obesity and hyperglycemia [6]. Thanks to their sedative action, they have been also used to treat insomnia, cough attacks and bronchitis [7]; also, the "Doum" has shown anti-inflammatory, anabolic, antiseptic, urinary, antilithic and diuretic activities [4,7,8]. Leaf extracts have also been reported to possess antioxidant activity and the ability to inhibit lipoxygenase [9,10].
The phytochemical properties of C. humilis are so far only little characterized. The analysis of the grain's oil showed higher levels of oleic and linoleic acids than other seed oils, as well as a significant amount of tocopherols and tocotrienols [11].
Several biologically important secondary metabolites such as flavonoids, phenols, saponins, gallic tannins and terpenoids have been detected in the leaves and fruits of C. humilis L., which may explain the pharmacological effects mentioned above [4,7,9,12].
With regard to flavonoids, they have been previously reported as constituents of the Arecaceae family of plants, even though the literature lacks detailed information on the phytochemical composition of C. humilis. Further, no work has been so far devoted to the analysis of the volatile content of such a species.
The aim of this work was to determine the volatile and polyphenolic content of Moroccan Doum fruits (C. humilis L.) by GC-MS and HPLC-PDA/MS. In addition, the evaluation of the physico-chemical properties, and the antioxidant activities of the fruit extracts, was performed as well.
This study represents an effort to provide more reliable information about the antioxidant and beneficial health properties of such a species in order to promote its use in different food, pharmaceutical and supplement industries. Table 1 reports the physico-chemical parameters for the C. humilis fruit under investigation. The percentage of dry matter attained was equal to 69.6 ± 0.5, approximately indicating the presence of 30.4% water in these fruits. The latter value is twice as high than the one reported by Bouhafsoun et al. (17.4 ± 0.12%) [2]. On the other hand, another study showed a higher value (79.6 ± 0.04%) in Butia odorata, which belongs to the same family (Arecaceae) [13].

Physico-Chemical Parameters
The ash content revealed interesting amounts of minerals (3.0 ± 0.3). Such a value coincides with the mean value of ash content (2.4 to 5.0%) recommended by FAO [14], even though it is lower than that recently reported for the Algerian species (4.2 ± 0.7%) [2].
The TSS results showed a mean value of 15.2 ± 0.7%. Similar values were found in Butia odorata fruits (13.1-14.6%) [17], despite Ferrão et al. (2013) revealing, for the same species, a value of 9.5 ± 0.0% [13]. These results are not in agreement with other studies where values reported were 2.4% in leaves and rachis and 4% in fruits [2]. This can be directly related to the sugar content of the fruit samples, which have higher sugar content than other parts of C. humilis L. [2].
The S/A ratio was 10.3 ± 0.5%. Such a ratio is an important biochemical parameter that influences the taste and acceptability of the fruits. The high values of this ratio indicate good technological properties and consumer acceptance of these fruits [18,19]. The result achieved in this study falls within the range found for Butia odorata fruits (4.42-14.20%) [13]. On the other hand, the S/A ratio values of the C. humulis L. fruits investigated in this work showed higher values compared to those of B. capitata reported in the literature, 4.7-5.8% [20].
Results of RS and TS were equal to 18.1 ± 0.7% and 23.7 ± 0.9%, respectively. Vitamin C contents in Doum extracts were determined to be 31.5 ± 0.5 mg/g, which is slightly higher than other research (20.1 ± 0.5 mg/g) [21].
The refractive index values for the C. humilis L. in each extract were 1.3 ± 0.0 and 1.34 ± 0.0 for ethyl acetate (EtOAc) and methanol-water (MeOH-H 2 O), respectively. The ANOVA test (p > 0.05) showed that the difference between the fruits in IR was not significant.
With regard to lipid and protein contents, values of 0.7 ± 0.0% and 5.3 ± 1.5% were attained, respectively. A value of 0.6 ± 0.0 mg/g was attained for the MeOH-H 2 O extract, whereas they were absent in the EtOAc fraction. The low levels of protein content can be caused by the ultrasonic extraction, which leads to protein denaturation, as proven by some researchers [22].

Phytochemical Screening
The phytochemical screening of C. humilis was carried out, for the first time for a Moroccan species. The phytochemical tests revealed the presence of different chemical families, distributed for the studied species according to the solvent concentration used. Anthocyanins were not detected in any of the samples investigated. In the EtOAc extract, unsaturated sterols, terpenes and glycosides, which were absent in the crude extract, were revealed. On the other hand, in the crude extract, catechic tannins, anthracenosides, sterols and steroids were detected in high concentrations.
In the literature, the phytochemical properties of C. humilis are not well characterized, although several studies have reported the presence of tannins, flavonoids, saponins, sterols and terpenoids [10]. These results are similar to those found in samples from Algeria [23]. Notably, saponosides, responsible for many pharmacological properties, e.g., anti-inflammatory [24,25], were also detected in the extract of C. humilis. From the results achieved, such a species does contain important phytochemical constituents that may contribute to its anti-inflammatory and antioxidant activities ( Table 2).

Phytochemical Content and Antioxidant Ability
The spectrophotometric assays showed an important amount of polyphenols. Comparing the two extracts, the MeOH-H 2 O one showed the highest total polyphenolic (TPP) content, equal to 32.7 ± 0.1 mg GAE/g DM, with respect to the EtOAc extract, 3.6 ± 0.5 mg GAE/g DM ( Table 3). The same considerations can be made for the total flavonoid (TFv) and total tannin (TT) contents. Statistical analysis (ANOVA) showed that there was a highly significant difference in results (p < 0.001) between the different solvent concentrations, thus indicating an effect of the solvent concentration on the extraction of these compounds [26].

HPLC-PDA/MS Analyses
The analysis of the polyphenolic profile, achieved by HPLC-PDA of the EtOAc and MeOH-H 2 O extracts of C. humilis, is reported in Figure 2. A total of sixteen and thirteen different polyphenolic compounds were detected in both extracts, respectively. Tentative identification was based on combined data coming from retention times, PDA, MS and standard co-injection, when available (thirteen in EtOAc vs. twelve in MeOH-H 2 O extracts (Tables 5 and 6)). Interestingly, the totality of the polyphenolic compounds in both extracts belong to the hydroxycinnamic acids class, whereas only two flavonols were identified in both extracts. Most of the compounds were already reported as constituents of fruits of botanical species, belonging to the same family, e.g., ferulic acid, feruloylquinic acid, ferulic acid hexoside [33], p-Coumaric acid, dicaffeoylshikimic acid and isorhamnetindiglucoside [34]. Notably, 3-Caffeoylquinic acid and 3-Caffeoylquinic acid were reported as constituents of leaf extracts of C. humilis [10], whereas quinic acid, p-Coumaric, rutin and kaempferol were found in the fruits of the same species [23]. Cinnamoyl glucose and p-Coumaric acid ethyl ester are here reported for the first time.   The quantification was determined for three repetitions of different extracts of the same sample. As far as quantification is concerned (Table 7), ferulic acid in the EtOAc extract turned out to be the most abundant one (104.7 µg/g), followed by 5-Caffeoylquinic acid (36.5 µg/g). On the other hand, in the MeOH-H 2 O extract, chlorogenic acid (45.4 µg/g) was predominant, along with quinic acid (37.0 µg/g).
In total, 276.7 µg/g and 262.2 µg/g of polyphenolic compounds for the EtOAc and MeOH-H 2 O extracts of C. humilis, respectively, were attained. Such results are comparable with other Moroccan fruits, e.g., Ziziphus lotus, at least for the EtOAc extract (298.5 µg/g) [26].

Samples and Sample Extraction
Chamaerops humilis L. fruits were harvested in Tangier-Tetouan-Al Hoceima, an area located in the extreme north-west of Morocco. The samples were collected for 4 months (May, June, July and August 2018). All of the harvest areas were between the longitudes 5 • 94'84106 and the latitudes 35 • 44'701. The fruit harvesting was carried out at their physiological maturity in the early morning, transported in well-closed boxes and stored at −10 • C in the Materials and Resources Valorization Laboratory, Faculty of Sciences and Technology of Tangier. The extraction method employed was previously described by El Cadi et al. (2020) [26]. Briefly, 5 g of lyophilized powder underwent a defatting step by adding three times 50 mL of n-hexane; afterwards, it was dried and homogenized with 50 mL of two solvents with increased polarity, namely EtOAc and MeOH-H 2 O 80:20 (v/v). Each fraction was extracted by using an ultrasound bath (130 kHz) for 45 min. After centrifugation at 5000 g for 5 min, the supernatant was filtered through a paper filter, dried, reconstituted with MeOH-H 2 O and then filtered through a 0.45 µm Acrodisc nylon membrane (Merck Life Science, Merck KGaA, Darmstadt, Germany) prior to HPLC-PDA-ESI/MS analysis.

Physico-Chemical Analyses and Phytochemical Screening
Physico-chemical analyses and phytochemical screening were carried out according to a previously published work [26].

Analysis and Quantification of Phenolic Contents
TPP content was estimated using Folin-Ciocalteu method [35] and was expressed as mg of gallic acid (GAE)/g of dry mass (DM). TFv content was expressed as mg of quercetin (QE)/g of dry mass (DM) and quantified according to the method of Zhishen et al. [36]. TT content was determined by the vanillin method of Julkunen-Tiitto and expressed as mg (+)-catechin/g DW [37].

Statistical Analysis
The experiments were carried out in triplicate and the results were expressed as the average of the three measurements ± SD. The comparison of means between groups was performed with one-way analysis of variance (ANOVA) followed by a Tukey test. Differences were considered significant when p < 0.05 (Microsoft ® Office, Santa Rosa, California, CA, USA).

Conclusions
The present study aimed to elucidate the bioactive content of Chamaerops humilis L. fruits. Considering the two extracts tested, in terms of the antioxidant activity, the EtOAc one turned out to be the most active with respect to the MeOH-H 2 O. A total of 69 compounds belonging to different chemical classes were positively identified by GC coupled to MS, whereas sixteen and thirteen polyphenolic compounds were detected by HPLC-PDA/MS in both EtOAc and MeOH-H 2 O extracts, respectively. Such results demonstrate that this fruit can be used for industrial applications in food preparations. In addition, the data attained emphasize an interesting functional composition of the Chamaerops humilis L. fruits, which could be considered a valuable new co-product with commercial importance in the food industry.