Effect of some local plant extracts on fatty acid composition of fish (Alestes baremoze) during smoking and sun drying in the Far‐North region of Cameroon

Abstract The objective of this study was to assess the antioxidant activities of three plant extracts (Moringa oleifera leaves, Xylopia aethiopica fruits, and Allium cepa leaves) and to evaluate their effects on the preservation of fish polyunsaturated fatty acids (PUFAs) during smoking and sun‐drying processes. PUFAs are highly prone to oxidation during fish processing. The plant extracts were analyzed for their polyphenol contents and were evaluated for their total antiradical capacity. The polyphenol components of each plant were characterized. The hydroethanolic and aqueous extracts were added to the fish at concentrations of 3, 6, 9, and 12 g/L and 10, 20, 30, and 40 g/L, respectively. Butylated hydroxytoluene (BHT) was used as a positive control at a concentration of 2 g/L to compare the antioxidant effects of the plant extracts. The treated fish was subjected to smoking or sun drying and the fatty acid composition of the fish lipid extract was assessed. The results showed that the total polyphenolic, flavonoid, and tannin contents varied significantly from one plant extract to the other (p < .05). The radical scavenging and FRAP increased significantly with the concentration of the plant extracts (p < .05). An HPLC analysis of the extracts led to the preliminary identification of four hydroxycinnamic acids in M. oleifera and X. aethiopica, one anthocyanin and one flavone glycoside in M. oleifera, and four flavan‐3‐ols in X. aethiopica. Moreover, eight flavonols were preliminarily identified in the three plants. Compared to the control product, these plant extracts significantly protected fish PUFAs from oxidation (p < .05). The aqueous extract of A. cepa at 40 g/L better preserved omega‐3 in fish during smoking and sun drying than the control product. Incorporating the three plant extracts during smoking and sun‐drying processes can effectively preserve the PUFAs in fish. Therefore, these plants are viable sources of natural antioxidants in the preservation of fish products.


| INTRODUC TI ON
Fish has been widely used as an excellent source of animal protein and other nutrients.It is a food rich in proteins of high nutritional value, lipids, minerals, and vitamins (Hantoush et al., 2014).In Cameroon, the national average consumption of fish was estimated at about 18.4 kg/inhabitant/year (FAO, 2017).Eating fish can prevent consumers from various diseases such as high blood pressure, coronary heart disease, cancer, and inflammatory disease since fish provide omega-3 polyunsaturated fatty acids (PUFAs), eicosapentaenoic acid (EPA), docosahexaenoic (DHA) acids, and amino acids (Morales et al., 2015).
However, fish is one of the most fragile and perishable marine products after capture (Brigitte et al., 2005).The impediment in its preservation comes from its high moisture content (75%-80%) which constitutes a favorable environment for the development of bacteria.In developing countries, including Cameroon, smoking and sun drying are choice processes used to limit the deterioration of fresh fish and increase its shelf life (Kumolu-Johnson et al., 2010).
However, during smoking and sun-drying processes of fish samples, the high temperatures and oxygen exposure lead to the oxidation of lipids content.Lipid oxidation can lead to changes in organoleptic properties, color, texture, appearance, and the release of undesirable flavors and odors (Kazuhisa, 2001).Extensive oxidation can also lead to a decrease in the nutritional properties of foods through the loss of components such as PUFAs (Cuvelier & Maillard, 2012).
Furthermore, these oxidative reactions can potentially produce toxic compounds through the release of free radicals and reactive oxygen molecules that are harmful to human health and are implicated in degenerative conditions such as cancer, cardiovascular diseases, and early aging (Krishnaiah et al., 2010).
In order to delay lipid oxidation, synthetic antioxidants such as butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), and tert-butyl hydroquinone (TBHQ) have been used to maintain the quality and extend the shelf life of oils.However, their use is increasingly being contested and has even been banned in certain countries due to their potential health risks which include cancer and cardiovascular diseases (Krishnaiah et al., 2010).Even so, many consumers have negative perception of the effect of synthetic antioxidant.In addition, BHA and BHT are quite volatile and easily decompose at high temperatures (Thorat et al., 2013).In order to overcome these challenges, food industries are searching for alternative antioxidants that are more stable and from natural sources, which in general, are supposed to be safer.
To expand these studies, other natural sources of antioxidants are required.According to literature, the antioxidant potential of natural plant extracts is mainly related to their content in phenolic compounds.M. oleifera, which grows naturally in many countries, is a powerful natural antioxidant because of its high content in flavonoids, tocopherols, vitamin C, and other phenolic compounds (Pakade et al., 2013).A. cepa is a common vegetable that is widely consumed all over the world.It is also a powerful natural antioxidant because it contains good amounts of flavonoids which are the largest group of phenolic compounds, along with quercetin (Archivio et al., 2007;Tiwari & Cummins, 2013).X. aethiopica also has a high level of phenolic compounds, flavonoids, and tannins; and demonstrates good antioxidant activity (Sokamte et al., 2019).
In the Far North Region of Cameroon, M. oleifera, X. aethiopica, and A. cepa grow in abundance and their leaves and fruits are highly consumed by the local populations.Their richness in polyphenols makes them good candidates for the evaluation of their antioxidant capacity during fish processing.The objective of this study was to investigate the effect of aqueous and hydroethanolic extracts of M. oleifera leaves, X. aethiopica fruits, and A. cepa leaves on the oxidative stability of processed fish by evaluating its fatty acid composition.

| Plant materials
The X. aethiopica fruits, and M. oleifera and A. cepa leaves used in this study were bought from the Maroua local market in March 2020.
This town is situated in the Far North Region of Cameroon and is located between Latitudes 10° and 13° North and Longitudes 13° and 16° East (RGPH, 2010).The samples were transported in sealed bags to the Food Biochemistry Laboratory of the University of Maroua.
The A. cepa leaves were washed with tap water, left to drain, and cut into small pieces.These cut leaves, the X. aethiopica fruits, and the fresh M. oleifera leaves were washed and dried at 50°C for 48 h in an electric air-dried oven (Memmert UN30, Zirndorf).The dried samples were ground using a blender (Panasonic) to obtain fine powders that can pass through a 0.5 mm sieve.The powders were then used for the preparation of the aqueous and hydroethanolic extracts.

| Animal material
Adult fish (A.baremoze) was bought from fishermen on the shores of Lake Maga (Far North Region of Cameroon) in April 2021.It was transported immediately in iceboxes to the Food Biochemistry Laboratory of the University of Maroua.After washing to remove external dirt and cleaning with disposable paper towels, the fish was eviscerated, washed anew with distilled water, and left to drain.The weight varied from 900 to 1000 g and the sizes were between 40 and 50 cm.

| Methods
Figure 1 presents flow diagram showing methodology followed in the experimentation and the analysis performed at each stage.

| Extraction of plant antioxidants
The extraction was performed according to the method described by Friedman et al. (2006).Twenty grams (20 g) of each plant powder were extracted with 500 mL of hydroethanolic mixture (40/60: v/v) for 48 h at room temperature (RT, ~24°C).The mixture was consistently shaken during the process and was strained through Whatman N° 4 filter paper.The residue was extracted again with 250 mL of the same solution to ensure maximum recovery of phenolic compounds.
The combined extracts were subjected to rotary evaporator at 40°C under reduced pressure to remove the solvent.The residue was obtained by drying the extract in an oven at 45°C until it became solid and of constant weight.
On the other hand, 20 g of each plant powder was dissolved in 500 mL of distilled water.The mixtures were heated to boiling point, submitted to reflux for 15 min, and were filtered through clean Whatman Paper N° 4 while hot.The filtrates (aqueous extracts) were cooled to RT, and then dried in an oven at 45°C until they became solid and of constant weight.They were then stored at 4°C prior to further analysis.

Determination of total phenolic content
The total phenolic content of the extracts was evaluated using the Folin-Ciocalteu colorimetric method as described by Gao et al. (2000).In a 5 mL test tube, 20 μL of a 2 g/L extract (water or aqueous ethanol) was added, followed by the Folin-Ciocalteu reagent (0.2 mL) and distilled water (2 mL).After incubating the mixture for 3 min at RT, 1 mL of 20% sodium carbonate solution was added and it was re-incubated for 2 h under the same conditions.The absorbance (Abs) of the resulting blue-colored solution was read at 765 nm with a spectrophotometer.The total phenolic content of the extract was calculated from the gallic acid (0-125 μg/mL) standard curve and was expressed in grams of gallic acid equivalents per 100 g of plant extract (g GAE/100 g of dry extract).

Determination of flavonoid content
The flavonoid content of the different samples was determined by the method of Mimica-Dukic´ (1992).Essentially, 0.1 g of each plant extract was homogenized with 10 mL of methanol.To 0.1 mL of the mixture diluted to a tenth was added 1 mL of aluminum chloride reagent (133 mg of crystalline aluminum chloride and 400 mg of crystalline sodium acetate dissolved in 100 mL of methanol).After homogenization, two drops of acetic acid were added.The mixture was homogenized again and Abs was read at 430 nm using a spectrophotometer.The quantity of flavonoids was calculated from the calibration curve of quercetin standard solutions (0-250 μg/mL) and expressed in grams of quercetin equivalents per 100 g of plant extract (g QUE/100 g of dry extract).

Determination of tannin content
Tannin levels in the plant extracts were determined by the method of Bainbridge et al. (1996).According to it, 0.1 g of each plant extract was homogenized with 10 mL of methanol.To 0.2 mL of the mixture diluted to a tenth were added 2 mL of reactive reagent (50 g of vanillin and 4 mL of hydrochloric acid in 100 mL of distilled water).The mixture was incubated at 30°C for 5 min and Abs was recorded at 500 nm with a spectrophotometer.The quantity of tannins was calculated from the calibration curve of catechin standard solutions (0-50 μg/mL) and expressed in grams of catechin equivalents per 100 g of plant extract (g CAE/100 g of dry extract).

Determination of antioxidant activities
DPPH free radical scavenging assay.The radical scavenging ability of the plant extracts was determined according to the method of Popovici et al. (2009).A total of 4.5 mL of a 0.002% (w/v) alcoholic solution of DPPH was added to 0.5 mL of different concentrations (125, 250, 500, 1000, and 2000 μg/mL) of samples and standard solutions in order to have final concentrations of 25-200 μg/mL.BHT, a synthetic antioxidant, was used as the positive control.The mixtures were kept at RT in the dark for 30 min, after which the Abs of the samples, control, and blank were measured at 517 nm in comparison with methanol.The antiradical activity (AA) was determined using the following formula: Ferric reducing antioxidant power (FRAP) assay.The antioxidant potential of the plant extracts was also evaluated by their ability to reduce iron (III) to iron (II) according to the method of Oyaizu (1986).Aliquots of 0.5 mL of plant extracts at various concentrations (125, 250, 500, 1000, and 2000 μg/mL) were individually added to 1 mL of phosphate buffer (0.2 M, pH 6.6) and 1 mL of 1% (w/v) aqueous potassium hexacyanoferrate solution, well shaken, and incubated at 50°C for 30 min.After incubation, 1 mL of 10% (w/v) TCA solution was added to stop the reaction, and the mixture was centrifuged at 3000 rpm for 10 min.A total of 1.5 mL of supernatant, 1.5 mL of distilled water, and 0.1 mL of 0.1% (w/v) ferric trichloride solution were mixed and incubated for 10 min, and Abs was read at 700 nm on a spectrophotometer.
Once more, BHT was used as the positive control.The reducing antioxidant power was calculated from the calibration curve of ascorbic acid (0-125 μg/mL) standard solutions, and expressed in

Ionization-Mass spectrometry (ESI-MS) analysis
The detection and identification of phenolic compounds in the three plant extracts were performed by HPLC paired with ESI-MS.
To that end, 50 mg of dried material was dissolved in 1200 μL of methanol containing 1% of acetic acid, followed by sonication By comparison with available standards, the retention times, UV-Vis spectra, full MS spectra, and MS/MS spectra were used for complete identification.When the standard was not available, the criteria were used for partial identification only.Quantifications were carried out by integration of the peaks on UV-Vis chromatograms at 280 nm for flavanols, 320 nm for hydroxycinnamic acids, 350 nm for flavonols, and 520 nm for anthocyanins.
(−)-Epicatechin, 5-caffeoylquinic acid, and procyanidin dimer B2 were quantified according to their own calibration curves, whereas other compounds were quantified "as equivalents" according to a reference compound belonging to the same polyphenol class and presenting a comparable UV-Vis spectrum.Thus, procyanidin oligomers were quantified in epicatechin equivalents, flavonols in hyperoside equivalents, and anthocyanins in ideain equivalents.

Preparation of plant extracts
The concentrations used were chosen according to Foffe et al. (2020) who proposed values and average yields of plant extracts.The average yields (~30%) and powder weights (10, 20, 30, and 40 g) were exploited to assess the mass (3, 6, 9, and 12 g) of crude concentrated hydroethanolic extracts.These crude extracts and BHT were dissolved each in 1 mL of ethanol and then in 1 L of distilled water to give concentrations of 3, 6, 9, and 12 g/L for the extracts and 0.2 g/L for the BHT.This synthetic antioxidant (BHT) was used at the legal limit of 0.2 g/L (Duh & Yen, 1997).Besides, 10, 20, 30, and 40 g of each plant powder were also dissolved in 1 L of distilled water.
The mixtures were then brought to boil and submitted to reflux for 15 min, after which they were filtered through clean Whatman Paper N° 4 while hot.The filtrates were then cooled to RT (Tenyang et al., 2020).

Fish treatment
The fish samples were treated and coded as follows: Control: Fish without extract and BHT (with water only); F: Fish; BHT: butylated hydroxytoluene; F + BHT0.2 g/L: Fish treated with butylated hydroxytoluene at concentration 0.2 g/L; F + MHE: Fish treated with M. oleifera hydroethanolic extracts; F + MAE: Fish treated with M. oleifera aqueous extracts; F + XHE: Fish treated with X. aethiopica hydroethanolic extracts; F + XAE: Fish treated with X. aethiopica aqueous extracts; F + AHE: Fish treated with A. cepa hydroethanolic extracts; F + AAE: Fish treated with A. cepa aqueous extracts.The hydroethanolic extracts were used at concentrations of 3, 6, 9, and 12 g/L while the aqueous extracts were used at concentrations of 10, 20, 30, and 40 g/L.The treated fish samples were divided into two parts and each part was subjected to smoking and sun-drying process.

Smoking
One batch of fish was treated to smoking using the previously mentioned experimental design.The samples were spread out on smoking trays which were then stacked on a smoking 0.9-m-high oven fired with hard wood and marked at temperatures greater than 70°C.
The process lasted for 12 h during which the samples were turned at intervals to ensure homogeneous drying.The dried smoked fish samples were packaged and sealed in bags that were stored at 4°C for further analyses.

Sun-drying
The treated fish was cut into two equal halves along its longitudinal body axis from mouth to tail but left attached at the tail region.
The pieces were then spread out on a traditional dryer braided with twigs of wood, exposed to open air, and protected by a mosquito net to prevent invasion by insects and other pests.They were subjected during the day (8 a.m.-5 p.m.) to ambient sunlight at temperatures between 25 and 40°C.The chunks were turned over from time to time to ensure homogeneous drying.The sun-drying process took 3 days due to the climatic conditions during the drying period, the moisture content of the air was comparatively low.The dried pieces were packaged and sealed in bags that were stored at 4°C for further analyses.

| Lipid extraction
Lipids were extracted from the raw and processed fish according to the Bligh and Dyer (1959) method.One hundred grams (100 g) of the commodity was placed in a blender (Panasonic) to which 100 mL of chloroform and 200 mL of methanol were added and blended for 3 min.This was followed by the addition of 100 mL of chloroform and 100 mL of distilled water.The mixture was blended again for 1 min and then filtered.The final extraction was ensured by the addition of more chloroform to attain a proportion of 2:2:1.8 of chloroform, methanol, and distilled water, respectively.After separating the different phases in a funnel, the organic phase was collected and dried using anhydrous sodium.The organic solvent was then eliminated using a rotary evaporator at 45°C under reduced pressure.The lipid extracts obtained were put in dark glass bottles and stored at −20°C for further analyses.

| Determination of fatty acid composition of lipid extracts
The fatty acid composition of the lipids extracted from the smoked and sun-dried fish was determined after transmethylation according to the method described by Morrison and Smith (1964).The analysis of the fatty acid methyl esters (FAME) was performed on a gas chromatograph (Clarus 690 GC, Perkin Elmer) paired with a splitless injector and a flame ionization detector.FAME were separated on a capillary column (DB 225, 30 m × 0.32 mm, film thickness 0.25 μm, Chromoptic) with H 2 as the carrier gas set at a constant flow of 2 mL/min.The chromatographic conditions applied were as previously described by Fogang et al. (2017).Individual fatty acids were identified by a comparison of their retention times with those of a standard mixture.Results were expressed in percentage of each fatty acid (FA) in relation to the total identified fatty acids (TFA -g/100 g TFA).The values ranged between 6.8 and 18.5 g GAE/100 g of dry extract, with XAE presenting the highest level (18.5 g GAE/100 g of dry extract).For the same plant, the aqueous extracts (AE) had higher values than the hydroethanolic extracts (HE).The total phenolic levels found were similar to those obtained by Sokamte et al. (2019) in some selected spices from Cameroon (7-20 g GAE/100 g of dry extract).However, the values obtained in this study were higher compared to those obtained by Mendoza-Taco et al. (2022) in Moringa oleifera extracts with 100% distilled water, 50% absolute ethanol, 50% distilled water, and 100% absolute ethanol (2.43, 1.10, and 2.61 g/100 g, respectively).The difference in the total phenolic content may be due to the state of physiological maturity of the plant and the solvent used (Du Toit et al., 2020;Oso & Oladiji, 2018).Condensed tannins are a group of phenolic compounds that result from the polymerization of flavanol units (Abdou et al., 2012).

| Statistical analyses
Their contents showed a significant variation among the plant extracts (p < .05),ranging from 0.09 to 1.74 g CAE/100 g of dry extract.

| DPPH test
The measurement of the ability of a molecule or substance to scavenge free radicals has become routine in testing the antioxidant property of plant extracts and is in fact their primary signature.The ability of an antioxidant to stabilize these radicals by donating its hydrogen is related to its potential capability to inhibit lipid oxidation (Matsubara et al., 1991) 2020) also demonstrated that M. oleifera, X. aethiopica, and A. cepa are powerful free radical scavengers.This observed effect could be due to their high phenolic content which, in many studies, has been reported to be related to antioxidant activity through this mechanism of action (Yin et al., 2019).It is also generally believed that the positions and total number of hydroxyl groups present in the aromatic constituents of the extracts offer better antioxidative properties (Parcheta et al., 2021).

| FRAP assay
The efficacy of a molecule or substance to reduce Fe 3+ into Fe 2+ by donation of its electron is also known as a good indicator of its antioxidant activity.The reaction leads to the formation of a Pearl's Prussian blue color which absorbs light at 700 nm (Seladji et al., 2014).Figure 3b shows the FRAP of the plant extracts compared to BHT.All the values were found to significantly increase with concentration (p < .05),and at 200 μg/mL, XAE exhibited the highest activity (2216.88mg AsAE/100 g).These observations indicated that the plant extracts were also powerful ferric reducers.The FRAP might be attributed to the presence of phenolic compounds, mainly flavonoids, that have been proven to be powerful metal reducers (Zhou & Tang, 2017).The polyphenolic compounds in the extracts appeared to function as good electron-and hydrogen-atom donors and therefore served to terminate radical chain reactions by converting free radicals to more stable products.The registered values were in correlation with those found by Sokamte et al. (2019)

| Elucidation of phenolic profiles of plant extracts by HPLC-DAD-ESI-MS
The HPLC-UV-visible/MS analysis of the methanolic extracts of the three plants is shown in Figure 4.The HPLC-UV profile permitted to detect the major phenolic compounds while the MS and MS/MS analyses identified them preliminarily.Thus, epicatechin and procyanidin B2 were fully identified (Table 1) according to a commercial standard while the other compounds were identified preliminarily, following UV-Visible, MS, and MS/MS data found in literature.The identification varied from one plant to the other.

| Effect of plant extracts on fatty acid composition of fish during processing
Changes in the fatty acid composition of oils extracted from smoked and sun-dried fish are presented in Tables 2 and 3, respectively.These processes significantly reduced the presence of PUFAs and omega-3 fatty acids in the fish (p < .05).Eicosapentaenoic acid (C20:5n-3, EPA) and docosahexaenoic acid (C22:6n-3, DHA) were the most affected.The percentage of loss of total omega-3 fatty acids was more than 85%.This decrease in the PUFA content of the lipids during the processing is potentially attributed to the structural and chemical changes induced in fish cells during exposure to sunshine and smoke.
The sun and high temperatures facilitate the attack of the double bonds of the unsaturated fatty acids, resulting in lipid oxidation and a decrease in the nutritive value of fish oil (Khaoula et al., 2013).
During smoking, AHE (12 g/L), MAE (40 g/L), and AAE (40 g/L) significantly protected the omega-3 fatty acids (p < .05),when compared to fish processed with water only (Table 2).On the other hand, all the extracts at the different concentrations significantly protected the omega-3 fatty acids during the sun-drying process (p < 0.05), when compared to fish processed with water only (Table 3).At 40 g/L, AAE protected more omega-3 fatty acids than all the extracts, including BHT at 0.2 g/L, during the two processes.Similar results were obtained by Chaula et al. (2019) who demonstrated that the aqueous extracts of Syzygium aromaticum and Kappaphycus alvarezii protected fish (Rastrineobola argentea) lipids against oxidation during sun drying.Messina et al. (2019Messina et al. ( , 2021) ) also showed that cold smoking combined with antioxidants had a positive effect on lipid peroxidation of meager (Argyrosomus regius) fillets, lower values of malondialdehyde, and protected omega-3 in fish during the process.Moreover, as in the case of Sander lucioperca filets, a fatty fish species, the lipid oxidation results showed that the combined application of Dunaliella salina as natural antioxidant and smoking significantly reduced the oxidation in Sander lucioperca in comparison with the batch that was only smoked (Bouriga et al., 2022).
This activity can be attributed to the polyphenolic compounds in these plant extracts (Figures 1 and 3).The hydrophobicity of quercetins (detected by HLPC mainly in the A. cepa leaves) makes them more soluble in lipids than other phenolic compounds.Indeed, quercetin and its derivatives scavenge free radicals and bind transition metal ions (Parcheta et al., 2021).This may justify why at a concentration of 40 g/L, the AAE provided better prevention of the oxidation of omega-3 fatty acids of fish during processing than the extracts of the other two plants and BHT at 0.2 g/L.According to Layé et al. (2015), the omega-3 fatty acids present in this fish (such as EPA and DHA) have preventive effects on human coronary artery and Alzheimer's disease.Previous research demonstrated that DHA is essential for the development of the fetal brain and the eye retina (San & Chew, 2005).According to Francesco and Tory (2007), flavonoids are the most abundant phenolic compounds in the plant.Figure 4 suggests that TA B L E 3 Changes in fatty acid composition of lipids extracted from sun-dried fish (%FA/TFA).

F
AA ( % ) = Abs control − Abs sample × 100 ∕ Abs control .fish milligrams of ascorbic acid equivalents per 100 g of plant extract (mg AsAE/100 g of dry extract) by using the following formula:where Fd = dilution factor, V = total extraction volume; Tp = test portion; a = slope of the calibration curve.
for 15 min (Brasson 2200, USA).The procedure was repeated three times and the combined extracts were filtered through an injection flask (Mini uniprep Whatman 0.45 μm) for HPLC and injected into an HPLC-UV-visible-DAD-ESI-MS system.The analytic device was composed of an SCM1000 degasification system (Thermo Scientific), an autosampler (Model Surveyor, Thermo Scientific), an 1100 series binary pump (Agilent Technologies), and a diode array UV-visible detector (DAD, UV6000 LP, Thermo Scientific).The mass spectrometer (MS) was an ion trap (LCQ Deca, Thermo Scientific) equipped with an ESI source.A sample volume of 2 μL was injected into a Purospher STAR Hibar HR RP18 column (150 mm × 2.1 mm, 3 μm, thermostated at 30°C, Supelco).The mobile phase consisted of Solvent A (aqueous solution of 0.1% formic acid, v/v) and Solvent B (acetonitrile containing 0.1% formic acid, v/v).The following linear gradient elution was applied at a constant flow rate of 0.2 mL/min: initial, 3% B; 0-3 min, 7% B, linear; 3-21 min, 13% B, linear; 21-27 min, 13% B, linear; 27-40 min, 30% B, linear; 40-51 min, 50% B, linear; 51-53 min, 90% B, linear; 53-56 min, 90% B, linear; 56-58 min, 3% B, linear; 58-72 min, 3% B, linear; followed by washing and reconditioning of the column.The UV-visible (UV-Vis) detection was performed in the 240-600 nm range.The ESI source was used in negative mode.The MS detection was carried out with the following parameters: MS spectra were acquired in full-scan negative ionization mode in the m/z 50-2000 range to obtain the signals corresponding to the deprotonated [M-H] − molecular ions.The method also included the MS/MS-dependent scan mode which was used to obtain the product ion spectrum of the main molecular ions detected on the chromatogram in the full-scan mode.The collision energy was optimized at 35% (arbitrary units) to clearly observe the production of both parent and main daughter ions.Data were collected and processed by XCalibur Software (Version 1.2, Thermo Finnigan).

Figure 2
Figure2shows the total phenolic, flavonoid, and tannin contents of the different plant extracts.The total phenolic content was found to vary significantly from one plant extract to the other (p < .05).

Flavonoids
constitute one of the most important phenolic groups in plants.Their contents varied significantly in the different plant extracts (p < .05),with values ranging from 1.4 to 11.2 g QUE/100 g of dry extract.The highest level was found in the M. oleifera hydroethanolic extracts (11.25 g QUE/100 g of dry extract).The values obtained were higher than those determined byAlikwe and Omotosho (2013) andOso et al. (2018)  on the same extract (4.90 g/100 g and 0.15 g/100 g) from Nigeria.
The XAE presented the highest quantities of condensed tannins (1.74 g CAE/100 g of dry extract), although the registered values were lower than those reported by Sokamte et al. (2019) from Cameroon (14.57g GAE/100 g).But, the values were higher than those observed by Hossain et al. (2020) (0.01 g GAE/100 g DM) inM.oleifera leaves methanolic extract.The difference noted may be due to the analytical techniques used, as well as the environment of the plant, the type of plant, the maturity, and/or the type of soil(Matinez-Ramos et al., 2020;Mykhailenko et al., 2020).
. The DPPH radical has the capacity to extract labile hydrogen atoms.The ability of the plant extracts to scavenge the DPPH radical in comparison to BHT is presented in Figure 3a.It was observed that for all the solutions, this activity significantly increased with concentration (p < .05),and the XAE always had the highest values.It was therefore clear that the aqueous extracts, like BHT, are powerful free radical scavengers.Mendoza-Taco et al. (2022), Oguntona et al. (2022), and Óscar et al. (
-UV-visible/MS and MS/MS identification and quantification of the main simple phenolic compounds in Moringa oleifera leaves, Xylopia aethiopica fruits, and Allium cepa leaves.

Figure 5
Figure 5 shows the biplot of the principal component analysis (PCA) of the phenolic compounds and the antioxidant activities of the plant extracts.Two components proved to be more interesting for the analysis: Principal Component 1 (F1) and Principal Component 2 (F2).They represented 91.72% of the initial variables, with 64.21% and 27.51% for the F1 and F2 axes, respectively.The PCA makes it possible to visualize the distribution of the various plant extracts which are presented in the form of points, according to Principal Components 1 and 2. The vectors representing the phenols, flavonoids, tannins, DPPH, and FRAP are oriented in one direction, pointing to the positive part of F1, while the tannins, FRAP, and DPPH point to the negative part of F2 and the phenols and flavonoids are in its positive part.The vectors are all quite far from 0, and the angles they form are less than 90°C.This suggests that the methods (FRAP and DPPH) correlate with the phenolic compounds which could be responsible for the scavenging of the DPPH • radical and the ferric reducing powers observed previously.The strong positive correlation between the tannins and FRAP (r = .88;p < .05)and the tannins and DPPH (r = .82;p < .05)shows that the antioxidant powers of the extracts seem to be more related to the presence of these compounds.Flavonoids are the most abundant of the two groups of phenolic compounds analyzed because they are more correlated with the total phenols (r = .57;p < .05).This observation correlates with the results of the phenol composition.
Identified according to a commercial standard or standard purified in the laboratory.Identified according to the m/z and UV-visible data found in literature.Changes in fatty acid composition of lipids extracted from smoked fish (%FA/TFA).Note: Mean values in the same column with different superscript letters are significantly different (p < .05).Abbreviations: BHT, butylated hydroxytoluene; Control, fish without extract and BHT; FA, fatty acid; FF, fresh fish; F + BHT0.2 g/L, fish treated with BHT at 0.2 g/L concentration; F + MHE, fish treated with M. oleifera hydroethanolic extracts; F + MAE, fish treated with M. oleifera aqueous extracts; F + XHE, fish treated with X. aethiopica hydroethanolic extracts; F + XAE, fish treated with X. aethiopica aqueous extracts; F + AHE, fish treated with A. cepa hydroethanolic extracts; F + AAE, fish treated with A. cepa aqueous extracts; 12 g/L, concentration of hydroethanolic extracts; 40 g/L, concentration of aqueous extracts; MUFA, monounsaturated fatty acid; PUFA, polyunsaturated fatty acid; SFA, saturated fatty acid; TFA, total fatty acid.