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Effects of Ethanolic Leaf Extracts of Neem (Azadirachta indica) on Oxidative Stability of Palm Oil



Enenche Daniel Elaigwu, Ogo Agbor Ogo, Esienanwan Esien Efiong and Obochi Godwin Oche
 
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ABSTRACT

Background and Objective: The search for natural alternatives in oil and food preservation is on the increase considering the potential health impact of using synthetic antioxidants. It is in attempt to bridge this gap that this study was designed to test the potency of leaf extract of neem (Azadirachta indica) in reducing peroxidation and stabilizing palm oil during storage. Materials and Methods: The neem leaf extract was carried out by cold maceration using ethanol as the extraction solvent. The ethanolic leaf extract was then evaluated for chemical composition using GCMS and UV-spectroscopy. Antioxidant activity on the extract was determined by 1,1-diphenyl-2-picrylhydrazyl (DPPH); β-carotene linoleic antioxidant activity, oxygen reducing antioxidant capacity (ORAC) and ferric reducing antioxidant power (FRAP) efficacy using standard procedures. Oil samples were prepared and treated with the plant leaf extracts using four different concentrations (100, 200, 400 and 800 mg L1) on storage for 6 months. Thereafter, chemical properties of the oil samples including peroxide value, anisidine value, iodine value, acid value, saponification value as well as sensory evaluation was also conducted on monthly basis throughout the storage period. Results: The results revealed the presence of certain bioactive compounds and their functional groups previously shown to facilitate antioxidant activities. Similarly, the extract had significant antioxidant effect for DPPH (12.5400±0.0173 IC50 (%) inhibition); β-carotene linoleic antioxidant activity (43.8233±0.0251 IC50 (%) inhibition), ORAC (4.6500±0.0200 μ Mol TE g1) and FRAP (286.4267±0.0378 μ Mol Fe2+ L1). Oil samples treated with the leaf extracts during storage show significant retardation of oxidation compared to untreated samples. In addition, sensory evaluation on a five-point hedonic scale revealed that all samples were generally acceptable. Conclusion: This study has given plausible evidence to support the use of Azadirachta indica as a natural antioxidant to prevent vegetable oils oxidation during prolonged storage.

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Enenche Daniel Elaigwu, Ogo Agbor Ogo, Esienanwan Esien Efiong and Obochi Godwin Oche, 2019. Effects of Ethanolic Leaf Extracts of Neem (Azadirachta indica) on Oxidative Stability of Palm Oil. Research Journal of Phytochemistry, 13: 1-10.

DOI: 10.3923/rjphyto.2019.1.10

URL: https://scialert.net/abstract/?doi=rjphyto.2019.1.10
 
Received: January 04, 2019; Accepted: February 15, 2019; Published: May 09, 2019

INTRODUCTION

The oil palm (Elaeis guineensis) is one of the important economic crops in the tropics. The primary products of the oil palm are palm oil (from the mesocarp) and palm kernel oil obtained from the kernels (seeds), which are derived through different processing techniques. However, edible oils (palm oil inclusive) are highly susceptible to oxidative deterioration and consequent production of undesired flavour during prolonged storage due to multiple environmental and storage conditions1. Oil instability is the inability of oil to remain stable due to the presence of acyl lipids such as monomeric, dimeric and oligomeric triacylglycerols and hesterols and phytosterols, which can oxidize on exposure to air or presence of moisture at high temperature to form lipid oxidation products with initial reaction products known as hydroperoxides and later form compounds such as aldehydes, ketones, alcohols and carboxylic acids2,3. The overall effect is seen in impaired palatability and avoidable economic loss resulting from changes in chemical composition4 capable of impairing acceptability. Lipid oxidation depletes important qualities of oils and reduces organoleptic characteristics of the foods they are used to prepare5. The abnormal sensory characteristics of oils that have undergone rancidity are paint-like or acrid (burning) odour and abnormal taste. The shelf life of edible oils is greatly dependent on their oxidative stabilities6 and this affects their applicability for both home and industrial purposes. Upon consumption, rancid oils form harmful free radicals in the body that lead to cellular damage with possible attendant health consequences such as those linked to diabetes and Alzheimer’s disease as well as digestive distress and depletion or impairment of absorption of Vitamins B and E in the gastrointestinal tract6. To reduce the susceptibility lipid oxidation that may lead to rancidity, edible oil industries use chemicals and synthetic antioxidants in preservation of oils7. However, the safety of synthetic additives has been questioned, which has stimulated researches to explore naturally-occurring alternatives with comparable antioxidative properties and health benefits. As previously reported, many natural antioxidants like ginger extract, raspberry leaves, pussy willow extract, olive leaf juice have been used to protect oxidizable constituents of essential oils from oxidation with consequent improvement in shelf life8,9. However, natural antioxidants have not been used on a large commercial scale owing to their high input cost, seasonal availability of their sources and a lack of robust scientific and technological evidence in support of their safe, nutritious and sensory parameters. Consequently, a commonly available and easily accessible source of promising phytochemicals is now the interest of many researchers10. Few studies have highlighted the medicinal importance of neem leaf and seed11,12. However, there is paucity of information and evidence in support of its antioxidant potential, particularly as it relates to oxidative stabilisation of edible oils for extended period of storage. This research work was therefore; designed to explore the antioxidant potential of graded concentrations of neem plant extracts using palm oil as an oxidation substrate on the basis of certain chemical and sensory parameters.

MATERIALS AND METHODS

Place and time: This research was conducted at the Centre for Food Technology and Research Laboratory, Benue State University, Makurdi, Benue State, Nigeria. Implementation was between February-September, 2018.

Sample collection: Mature Azadirachta indica (NM) leaves were collected from Makurdi metropolis and were properly identified by a botanist at the Department of Biological Sciences of Benue State University. The leaves were washed under running tap water and air-dried for 3 days and subsequently crushed mechanically to obtain a suitable surface area. The resulting samples were then dried at room temperature in the shade to avoid exposure to sunlight for 2 h before being stored for further analysis. Palm oil sample was collected from Seasons Oil Processing Mill, Abia State, Nigeria and kept in tightly sealed MacCakney bottles prior to storage.

Extraction of neem leaf extract: Extraction of leaf extracts was done by cold maceration according to the method described by Hossain et al.11 and Evbuomwan et al.12. About 500 g of ground leaves were weighed into 4000 mL of ethanol and the solution was macerated for about 24 h with gentle shaking at 360 rpm until the soluble matter had properly dissolved. After extraction, the solution was clarified by filtration under vacuum using Whatman filter paper and the ethanol solvent evaporated completely using a rotary evaporator. The solvent free ethanol crude extract was suspended in diethyl ether to purify the extract after which it was exposed to the atmosphere for a while to ensure elimination of the solvent odour. The extracts obtained were then weighed and refrigerated for further analysis.

Phytochemical screening and quantitation
Determination of total phenolic content: The total phenolic content of the leaf extracts of the samples was determined by taking 20 μL of the extract in a screw capped 11 mL test tube, together with 1.6 mL distilled water and Folin-Ciocalteu reagent (100 μL). All were mixed with each other, then 300 μL of 20% Na2CO3 solution added and well shaken in a shaking water bath at 40°C for 30 min and total phenolic content determined from the standard curve plotted by using gallic acid as standard at 760 nm, according to the method of Anwar et al.13.

Determination of total flavonoid content: The total flavonoid (TF) content of the extracts was quantified according to the method described by Dewanto et al.14 and the results determined as catechin equivalents (mg/100 g of dry weight). At a concentration of 1 mg mL1, the extracts were diluted with 4 mL of water in a 10 mL volumetric flask. Initially, 0.3 mL of 5% NaNO2 solution was added to each volumetric flask; at 5 min, 0.3 mL of 10% AlCl3 is added and at 6 min, 2 mL of 1.0 mol L1 NaOH was added before 2.4 mL water was added to the reaction flask and mixed well. Absorbance of the reaction mixture was read at 510 nm.

Determination of tannins: Determination of tannins was carried out by the method described by Wahab and Elabor15. About 0.2 g of sample was measured into a 50 mL beaker. About 20 mL of 50% methanol added and covered with paraffin and placed in a water bath at 77-80°C for 1 h and stirred with a glass rod to prevent lumping. The extract was quantitatively filtered using a double layered Whatman No.1 filter paper into a 100 mL volumetric flask using 50% methanol to rinse. This was then made up to mark with distilled water and thoroughly mixed. About 1 mL of sample extract was then pipette into 50 mL volumetric flask, 20 mL distilled water, 2.5 mL Folin-Denis reagent and 10 mL of 17% Na2CO3 then added and mixed properly. The mixture was made up to mark with distilled water, mixed well and allowed to stand for 20 min till a bluish-green colouration developed. Standard tannic acid solutions of range 0-10 ppm was treated similarly as 1 mL of sample above. The absorbances of the tannic acid standard solutions as well as samples are read after colour development on a spectrophotometer at a wavelength of 760 nm. Percentage tannin was calculated using the equation:

Gas chromatography-mass spectroscopy analysis: The gas chromatography-mass spectroscopy (GC-MS) analysis was done with SHIMADZU, Japan GCMS-QP2010 PLUS. The GC-MS analysis was undertaken to detect the organic compounds present in A. indica ethanolic leaf extract. Each chemical constituent of extract was compared with NIST05s LIB by matching with the mass spectra of published data.

Fourier transform infrared (FT-IR) spectroscopy: A SHIMATZU FTIR-8400S Japan (KBr) spectrophotometer was used for the recording. About 10 mg of dried A. indica ethanolic leaf extract powder was encapsulated in 100 mg of KBr pellet, in order to prepare translucent sample discs. The powdered sample of each plant specimen was loaded in FTIR spectroscope with a Scan range from 400-4000 cm1 with a resolution of 4 cm1.

Determination of antioxidant activity
DPPH radical scavenging activity (DRSA): Initial DPPH assay on TLC plate was done and then the antioxidant activity of the different crude extracts was evaluated as described by Hossain et al.11 with modification. About 4 mL of each concentration was placed in a working test tube and then DPPH (2,2-diphenyl-1-picrylhydrazyl) (1 mL, 0.1 mM, methanol) added to the test tube and shaken vigorously. After shaking, all the test tubes were allowed to stand at 27°C in a dark place for 45 min. A control sample was prepared according to the same procedure without any extract. The absorbance of the tested samples was then be measured by UV spectrophotometer at the wavelength 517 nm. The antioxidant activity of each sample was expressed in terms of concentration required to inhibit DPPH radical formation by 50% (IC50 μg mL1) and calculated from the log-dose inhibition curve:

Where:
Ac : Absorbance of control is the absorbance in absence of standards or extracts
At : Absorbance of sample is the absorbance in presence of standards or extracts

Oxygen radical absorbance capacity (ORAC): The method employed by Girgih et al.16 was used. The samples were dissolved in sodium phosphate buffer (75 mM, pH 7.4) and then mixed with 300 nM fluorescein in a 96-well microplate followed by incubation of the mixture in the dark at 37°C for 15 min (final peptide concentration of 1 mg mL1). Thereafter, a 50 μL aliquot of 80 mM 2,2l-azobis (2-amidinopropane) dihydrochloride (AAPH) was added to the mixture and the change in fluorescence due to AAPH-induced oxidation of fluorescein measured at 1 min intervals for 90 min at excitation and emission wavelengths of 485 and 528 nm, respectively, using a fluorescence microplate reader. Different concentrations of Trolox (5-80 μM) was used to prepare a standard curve and the ORAC values of the samples calculated as follows:

where, ORAC values were expressed as μM T trolox equivalent (TE) g of sample.

Ferric reducing antioxidant power (FRAP): The method employed by Girgih et al.16 was used. About 250 μL of the sample was dissolved in 0.2 M sodium phosphate buffer at pH 6.6 and blank (250 μL of buffer) was mixed with 250 μL of same buffer followed by addition of 250 μL of 1% (w/v) potassium ferricyanide solution. Thereafter, 250 μL of peptide/TCA mixture was combined with 50 μL of 0.1% (w/v) ferric chloride and 200 μL of double distilled water and allowed to stand at room temperature for 10 min. The solution was then centrifuged at 10,000 rpm and 200 μL of the clear supernatant transferred to a 96-well plate for determination of the absorbance of the supernatant at 700 nm.

β-carotene bleaching antioxidant assay: In this assay the antioxidant capacity of A. indica was determined in emulsion by the β-carotene bleaching method of Farag et al.17 consisting in a coupled oxidation of linoleic acid and β-carotene. A stock solution of β-carotene/linoleic acid (Sigma-Aldrich) was prepared as follows. β-carotene (0.5 mg) was dissolved in 1 mL of chloroform (HPLC grade), then 25 μL of linoleic acid and 200 mg of Tween 40 (Merck) were added. The chloroform was subsequently evaporated, then distilled and oxygenated water (100 mL) was added with vigorous shaking. Aliquots (2.5 mL) of the stock solution were transferred to test tubes and 300 mL portions of the extracts (1 g L1 in methanol) were added before incubating for 48 h at room temperature. The antioxidant activity was evaluated by absorbance measurement at 470 nm against a blank containing emulsified linoleic acid without β-carotene.

Preparation of oil samples for storage: The leaf extracts of A. indica was added to the palm oil samples in four concentrations of 100, 200, 400 and 800 mg L1. The acceptable maximum concentration of 100 mg L1 of butylated hydroxyl toluene (BHT) was added to another portion of the oils to act as standard while a sample without extract or BHT was used as the control. All samples were measured into 100 mL polyethylene terephthalate (PET) bottles, cork screwed and labeled as P100 (Palm oil+ 100 mg L1 neem leaf extract), P200 (Palm oil+200 mg L1 neem leaf extract), P400 (Palm oil+400 mg L1 neem leaf extract), P800 (Palm oil+800 mg L1 neem leaf extract), PBHT (Palm oil+100 mg L1 Butylated Hydroxyl Toluene) and PCONT (Palm oil Control without extract). They were then kept in a dark cupboard were samples were taken for analysis each month.

Determination of peroxide value: Peroxide value was determined by iodometric titration which measures the iodine produced from potassium iodide by peroxides present in the oil, according to the method described by Jacobs18.

Determination of anisidine value: Anisidine values (AV) were determined according to AOAC19 ISO Method 6885 by measuring the absorbance of p-anisidine at 350 nm on a JENWAY 7315 UV-spectrophotometer.

Determination of acid value: The acid value were determined according to the AOAC19 official method using 0.5 N potassium hydroxide to titrate 2 g of oil in 50 mL mixture of dietylether and ethanol until a pink colour was obtained.

Determination of iodine value: The Wijs method described by Nadeem et al.20 was employed in determination of iodine value.

Sensory evaluation: Sensory evaluation of oil samples and control were carried out at 25°C in a well illuminated laboratory. Samples of the oils were randomly served to a panel of 25 trained judges and all orders of servings fully randomised. Sensory evaluation was done using a descriptive 5-point Hedonic scale. The rating was 5 very desirable and 1 undesirable for all parameters evaluated, which included colour, appearance, odour, flavor and texture.

Statistical analysis: Data is presented as mean±standard deviation of two replicates and analyzed by one-way ANOVA using statistical products and service solutions (SPSS) software version 21 (SPSS Ltd., USA). Multiple comparisons (post hoc Duncan multiple range test) were used to evaluate significant differences of the data at p<0.05 confidence limit.

RESULTS

Phytochemical composition of A. indica leaf extracts: The results of phytochemical screening and quantitative phytochemical determination of A. indica are shown in Table 1 and 2. Azadirachta indica showed positive identification for tannins, saponins, alkaloids, phenolics, flavonoids, glycosides and terpenoids with phenolics recording the highest amount (6624.920±4.670) while tannins recorded the least amount of 131.850±0.55 μg mL1.

Antioxidant activity of A. indica leaf extracts using different methods: Results of antioxidant activity of A. indica is presented in Table 3 with the extracts showing comparative antioxidant property to its synthetic counterpart.

GC-MS analysis of A. indica leaf extracts: The GC-Mass spectra of the ethanolic extracts of Neem leaves is presented in Fig. 1 and the compounds present identified as shown in Table 4. The fragmentation patterns of the mass spectra were compared with those of the known compounds stored in the National Institute of Standards and Technology (NIST) research library.

FTIR analysis of A. indica leaf extracts: The FTIR spectra given in Fig. 2 revealed different characteristic peaks corresponding to various functional groups characterizing A. indica that may be responsible for the antioxidant properties of the extracts.

Peroxide values of oil samples on storage: The peroxide values of treated oil samples and control are presented in Table 5. Range of peroxide values for treated samples denoted by P100-P800 for concentration of extracts were from 0.695±0.001-0.921±0.000 meq kg1 at first month and 4.266±0.003-7.923±0.004 meq kg1 by end of storage, which are comparatively lower than the values of the control group.

Table 1:Qualitative phytochemical screening results of A. indica leaf extracts
+: Present, -: Absent

Table 2:Quantitative phytochemical determination A. indica leaf extracts
Values are mean±standard deviation for two independent determinations

Table 3: Antioxidant activity of A. indica leaf extracts
Values are mean±standard deviation for two independent determinations

Table 4:GC-MS result of chemical compounds present in A. indica leaf extracts

Table 5:Peroxide values (meq/1000 g) of palm oil treated with A. indica leaf extracts
5: Very desirable, 4: Desirable, 3: Acceptable, 2: Slightly undesirable, 1: Undesirable. Values are Mean±Standard deviation two independent determinations. Values with different superscripts are statistically significant (Duncan multiple range test) at p<0.05

Fig. 1:GC-MS chromatogram of A. indica leaf extracts

Fig. 2: FT-IR chromatogram of A. indica leaf extracts

However, the extract at 800 mg L1 gave a consistently lower values than others.

Anisidine value of oil samples on storage: Results for anisidine values of treated oils is reported in Table 6. Anisidine values in treated samples were significantly low and within recommended limits. They were higher than those recorded for samples treated with the synthetic antioxidant but lower than those for the control sample.

Acid values of oil samples on storage: Acid values of treated and untreated oil samples on accelerated storage are presented in Table 7.

Iodine values of oil samples on storage: The iodine values of treated oils are reported in Table 8. A steady but gradual decline in the iodine value was observed for all the samples in a concentration dependent manner.

Saponification values of treated oils: Saponification values of oil samples treated or untreated during the storage period is shown in Table 9.

Sensory evaluation of oil samples treated with extracts of A. indica: Results of sensory evaluation conducted by a trained panelists is presented in Table 10. The results indicate that oil samples treated with A. indica were generally acceptable for the selected parameters with higher scores recorded for samples with low concentration of extract.

Table 6:Anisidine values of palm oil treated with A. indica leaf extracts
5: Very desirable, 4: Desirable, 3: Acceptable, 2: Slightly undesirable, 1: Undesirable. Values are Mean±Standard deviation for two independent determinations. Values with different superscript are statistically significant (Duncan Multiple range test) at p<0.05

Table 7:Acid values (meq/1000 g) of palm oil treated with A. indica leaf extracts
5: Very desirable, 4: Desirable, 3: Acceptable, 2: Slightly undesirable, 1: Undesirable. Values are Mean±Standard deviation for two independent determinations. Values with different superscripts are statistically significant (Duncan Multiple range test) at p<0.05

Table 8:Iodine values (I2/100 g) of palm oils treated with A. indica leaf extracts
5: Very desirable, 4: Desirable, 3: Acceptable, 2: Slightly undesirable, 1: Undesirable. Values are Mean±Standard deviation for two independent determinations. Values with different superscripts are not statistically significant (Duncan Multiple range test) at p<0.05

Table 9:Saponification values (mg KOH g1) for palm oils treated with A. indica leaf extracts
5: Very desirable, 4: Desirable, 3: Acceptable, 2: Slightly undesirable, 1: Undesirable. Values are Mean±Standard deviation for two independent determinations. Values with different superscript are statistically significant (Duncan multiple range test) at p<0.05

Table 10:Sensory attributes of palm oil samples treated with A. indica leaf extracts, BHT and control
Values with different superscripts across the column differ significantly (Duncan Multiple range test) at p<0.05

DISCUSSION

The phenolic composition as determined in this study is in conformity with other findings, which correlated with extension of oil shelf life21. Similarly, the ability of phenolic compounds to enhance oxidative stability of oils has been reported by Baldioli et al.22. Although the interest in phenolic compounds is related primarily to their antioxidant activities, they also show an important biological activity in vivo and may be beneficial in combating diseases arising from exposure to excessive oxygen radical formation exceeding the antioxidant defense capacity of the living system. The values recorded for antioxidant assays carried out on the crude extracts of A. indica, which included DPPH radical scavenging assay, β-carotene linoleic antioxidant assay, oxygen reducing antioxidant capacity (ORAC) assay and Ferric reducing antioxidant power (FRAP) assay were comparable to those obtained by Baldioli et al.22. Although the values are higher than those of the synthetic antioxidant used, the health implications arising from continued use would make the natural alternative a preferable choice. Additionally, there is also the possibility of improving the radical scavenging property of the extracts if it undergoes refinement before usage, which is the focus moving forward in this research area.

The GC-MS data compared favorably with those reported by Prashanth and Krishnaiah23, revealing the presence of similar bioactive compounds. From the results, it was observed that presence of 3, 7, 11, 15-tetramethyl-2-hexadecen-1-ol (synonym: Phytol), 9, 12, 15- Octadecatrienoic acid (synonym: Linolenic acid; α-Linolenic acid), 8, 11, 14-Eicosatrienoic acid (Synonym: Homo-γ-linolenic acid), N-Hexadecanoic acid (synonym: Palmitic acid) and Tridecanoic acid (synonym: Tridecylic acid) were the major components in the extract. Phytol is reported to have antioxidant, antiallergic24, antinociceptive and anti-inflammatory activities25. Additionally, recent studies revealed that phytol is an excellent immunostimulant superior to a number of commercial adjuvants in terms of long-term memory induction and activation of both innate and acquired immunity26. Palmitic acid is reported to possess antibacterial and cholesterolaemic effects27. In addition, palmitic acid and linoleic acid extracted from plants have been shown to possess significant cytotoxic effects in some cancer cell lines including28 MOLT-4 in addition to the later’s inhibitory effect on oxidation. Thus, consumption of palm oil preserved with extracts of A. indica containing such active compounds may offer medicinal and antimicrobial benefit as well as nutritional importance. Thus, a combination of this and phenolic compounds found in A. indica should give confidence to the use of this plant as suitable antioxidant. The FT-IR data obtained in this study was similar to those reported by Ibrahim and Sani29. This may have been responsible for the beneficial chemical properties exhibited by the crude extract of the plant leaf in treated palm oil samples. However, further studies would be required to elucidate the structural identification of these constituents and the mechanisms of their actions in bequeathing antioxidant properties to the plant leaf and possible contribution to phytoremediation as a panacea for environmental degradation occasioned by oil spillage.

A measure of oxidative stability of the oil samples was determined through the measurement of peroxide values, anisidine value as well as iodine values. The range of peroxide values for treated samples (P100-P800) was comparable to the reports of Frank et al.30 but lower than those reported by Amata and Ozuor31, which may be due to the application of different plant extracts and techniques of extraction. The peroxide values recorded for samples treated with synthetic antioxidant (PBHT) were lower than the samples treated with the plant extract but higher than the control samples, indicating the potential of the plant extract to improve the oil quality upon storage. Generally, change in peroxide values was in a concentration-dependent manner and the values for all samples correspond to normal CODEX 210 values32, which recommended a maximum PV of 15 meq O2 kg1. Anisidine values for samples treated with the extracts were lower than those for the control sample indicating that the extract had significant effects in reducing anisidine value of palm oils upon storage. Again, it is observed that the anisidine value increased slightly but steadily as storage time extended and indicated that anisidine value reduced as the concentration of extracts increased. According to White33, an acceptable AV for well-refined oils is between 1 and 10 mmol kg1, whereas oils with high levels of polyunsaturated fatty acids might have higher levels even when fresh. Acid values showed a gradual decline in values as concentration of A. indica increased similar to reports by Van der Merwe et al.34 who observed a gradual and then sharp increase in free fatty acid in oil stored over 52 weeks. The trend shown in iodine value establishes a relationship between extract efficacy and oil saturation. In general, the greater the degree of unsaturation, the more readily the oil or fat becomes rancid. This trend was similarly observed for saponification value, which was found to be higher than previous studies35,36. Saponification values fell within range set by both national and international regulatory agencies. Since hydrolysis depletes esters, this accounts for why there is a decrease in the saponification value of oil samples in agreement with the findings of Akubor and Ogu37.

Results of sensory evaluation showed that sample treatment with A. indica leaf extracts were generally acceptable. However, in terms of appearance and colour, control sample was most desirable. The presence of green pigments in treated oil samples may have impacted on the appearance and colouration of the oil, which may affect their high rating on the scale.

CONCLUSION

This study showed that ethanolic extracts of A. indica has constituents that have been severally reported to have antioxidant properties including phytol and palmitic acid and other important phytochemicals. This assertion was confirmed by the antioxidant assays, which showed significant radical scavenging ability for the extracts as well as oxygen reducing antioxidant power with lower IC50 doses compared to standard antioxidants. In addition, the results also clearly indicated that the oxidative stability of palm oil significantly (p<0.05) improved by the application of A. indica ethanolic extracts in the order P800 P400 P200 P100, making the plant leaf a promising alternative for synthetic antioxidants for oil preservation. The encouraging sensory acceptability also affirms that palm oil treated with A. indica are marketable with good economic potential.

SIGNIFICANCE STATEMENT

As concerns for use of synthetic chemicals such as preservatives and other additives continue to grow, the need to embrace healthier alternatives becomes more imperative. This study discovered that A. indica leaf extracts contain valuable health-promoting phytochemicals and possess antioxidant ability in preventing oil spoilage, thus documenting important contributions to evidence in support of natural preservatives. This discovery is key to streamlining key suspects that would enable other researchers explore further details on the candidate plant.

REFERENCES
AOAC., 2000. Official Methods of Analysis. 17th Edn., Association of Official Analytical Chemist, Washington, DC., USA.

Ajani, E.N., E.A. Onwubuya and H.U. Nwalieji, 2012. Assessment of oil palm production and processing among rural women in Enugu North agricultural zone of Enugu State, Nigeria. Int. J. Agric. Sci., 2: 322-329.
Direct Link  |  

Akinola, F.F., O.O. Oguntibeju, A.W. Adisa and O.S. Owojuyigbe, 2010. Physico-chemical properties of palm oil from different palm oil local factories in Nigeria. J. Food Agric. Environ., 8: 264-269.
Direct Link  |  

Akubor, P. and G.I. Ogu, 2012. Quality attributes of fresh palm oils produced from selected communities around Anyigba, Kogi state, Nigeria. Niger. J. Nutr. Sci., 33: 12-17.
Direct Link  |  

Aluyor, E.O. and M. Ori-Jesu, 2008. The use of antioxidants in vegetable oils-A review. Afr. J. Biotechnol., 7: 4836-4842.
Direct Link  |  

Amata, I.A. and E. Ozuor, 2013. The effect of different processing methods on the quality of Crude Palm Oil (CPO) in Delta North agricultural zone of Delta State Nigeria. Int. J. Agric. Biosci., 2: 116-119.
Direct Link  |  

Anwar, F., A. Siddiq, S. Iqbal and M.R. Asi, 2007. Stabilization of sunflower oil with Moringa oleifera leaves under ambient storage. J. Food Lipids, 14: 35-49.
CrossRef  |  Direct Link  |  

Azeez, O.T., K.O. Ejeta, E.O. Frank and N.E. Gerald, 2013. Effects of antioxidants on the oxidative stability of vegetable oil at elevated temperature. Int. J. Applied Sci. Technol., 3: 107-115.
Direct Link  |  

Baldioli, M., M. Servili, G. Perretti and G. Montedoro, 1996. Antioxidant activity of tocopherols and phenolic compounds of virgin olive oil. J. Am. Oil Chem. Soc., 73: 1589-1593.
CrossRef  |  Direct Link  |  

Codex Alimentarius Commission, 2005. Codex standard for named vegetable oils (CODEX-STAN 210-1999). Codex Alimentarius Commission, Joint FAO/WHO Food Standards Programme, Rome, Italy.

Coelho, D.F., L.O. Pereira-Lancha, D.S. Chaves, D. Diwan and R. Ferraz et al., 2011. Effect of high-fat diets on body composition, lipid metabolism and insulin sensitivity and the role of exercise on these parameters. Braz. J. Med. Biol. Res., 44: 966-972.
CrossRef  |  Direct Link  |  

Dewanto, V., X. Wu, K.K. Adom and R.H. Liu, 2002. Thermal processing enhances the nutritional value of tomatoes by increasing total antioxidant activity. J. Agric. Food Chem., 50: 3010-3014.
CrossRef  |  Direct Link  |  

Evbuomwan, B.O., I. Felix-Achor and C.C. Opute, 2015. Extraction and characterization of oil from neem seeds, leaves and barks. Eur. Int. J. Sci. Technol., 4: 1-7.
Direct Link  |  

Fan, L. and N.A.M. Eskin, 2015. The Use of Antioxidants in the Preservation of Edible Oils. In: Handbook of Antioxidants for Food Preservation, Shahidi, F. (Ed.). Chapter 15, Woodhead Publishing, USA., ISBN-13: 978-1-78242-089-7, pp: 373-388.

Farag, R.S., A.Z.M.A. Badei, F.M. Hewedi and G.S.A. El-Baroty, 1989. Antioxidant activity of some spice essential oils on linoleic acid oxidation in aqueous media. J. Am. Oil Chem. Soc., 66: 792-799.
CrossRef  |  Direct Link  |  

Farag, R.S., E.A. Mahmoud and A.M. Basuny, 2007. Use crude olive leaf juice as a natural antioxidant for the stability of sunflower oil during heating. Int. J. Food Technol., 42: 107-115.
CrossRef  |  Direct Link  |  

Frank, N.E.G., M.M.E. Albert, D.E.E. Laverdure and K. Paul, 2011. Assessment of the quality of crude palm oil from smallholders in Cameroon. J. Stored Prod. Postharvest Res., 2: 52-58.
Direct Link  |  

French, M.A., K. Sundram and M.T. Clandinin, 2002. Cholesterolaemic effect of palmitic acid in relation to other dietary fatty acids. Asia Pac. J. Clin. Nutr., 11: S401-S407.
CrossRef  |  Direct Link  |  

Gallego, M., M. Skowyra, M. Gordon, N. Azman and M. Almajano, 2017. Effect of leaves of Caesalpinia decapetala on oxidative stability of oil-in-water emulsions. Antioxidants, Vol. 6, No. 1. 10.3390/antiox6010019

Girgih, A.T., D. Chao, L. Lin, R. He, S. Jung and R.E. Aluko, 2015. Enzymatic protein hydrolysates from high pressure-pretreated isolated pea proteins have better antioxidant properties than similar hydrolysates produced from heat pretreatment. Food Chem., 188: 510-516.
CrossRef  |  Direct Link  |  

Hameed, A., S.A. Hussain, J. Yang, M.U. Ijaz, Q. Liu, H.A.R. Suleria and Y. Song, 2017. Antioxidants potential of the filamentous fungi (Mucor circinelloides). Nutrients, Vol. 9, No. 10. 10.3390/nu9101101

Harada, H., U. Yamashita, H. Kurihara, F. Fukushi, J. Kawabata and Y. Kamei, 2002. Antitumor activity of palmitic acid found as a selective cytotoxic substance in a marine red alga. Anticancer Res., 22: 2587-2590.
PubMed  |  

Hossain, M.A., W.A.S. Al-Toubi, A.M. Weli, Q.A. Al-Riyami and J.N. Al-Sabahi, 2013. Identification and characterization of chemical compounds in different crude extracts from leaves of Omani neem. J. Taibah Univ. Sci., 7: 181-188.
CrossRef  |  Direct Link  |  

Ibrahim, M.B. and S. Sani, 2015. Neem (Azadirachta indica) leaves for removal of organic pollutants. J. Geosci. Environ. Protect., 3: 1-9.
CrossRef  |  Direct Link  |  

Iqbal, S. and M.I. Bhanger, 2007. Stabilization of sunflower oil by garlic extract during accelerated storage. Food Chem., 100: 246-254.
CrossRef  |  Direct Link  |  

Jacobs, M.B., 1999. The Chemical Analysis of Foods and Food Products. 3rd Edn., Litton Educational Publishing Inc., USA., ISBN-13: 978-8123906430.

Lim, S.Y., M. Meyer, R.A. Kjonaas and S.K. Ghosh, 2006. Phytol-based novel adjuvants in vaccine formulation: 1. Assessment of safety and efficacy during stimulation of humoral and cell-mediated immune responses. J. Immune Based Ther. Vaccines, Vol. 4. 10.1186/1476-8518-4-6

Nadeem, M., M. Abdullah, I. Hussain, S. Inayat, A. Javid and Y. Zahoor, 2013. Antioxidant potential of Moringa oleifera leaf extract for the stabilisation of butter at refrigeration temperature. Czech. J. Food Sci., 31: 332-339.
Direct Link  |  

Onwuka, G.I. and B.I. Akaerue 2006. Evaluation of the quality of palm oil produced by different methods of processing. Res. Biol. Sci., 1: 16-19.
Direct Link  |  

Prashanth, G.K. and G.M. Krishnaiah, 2014. Chemical composition of the leaves of Azadirachta indica Linn (Neem). Int. J. Adv. Eng. Technol. Manage. Applied Sci., 1: 21-31.
Direct Link  |  

Ryu, K.R., J.Y. Choi, S. Chung and D.H. Kim, 2011. Anti-scratching behavioral effect of the essential oil and phytol isolated from Artemisia princeps Pamp. in mice. Planta Medica, 77: 22-26.
CrossRef  |  Direct Link  |  

Santos, C., M. Salvadori, V. Mota, L. Costa and A. de Almeida et al., 2013. Antinociceptive and antioxidant activities of phytol in vivo and in vitro models. Neurosci. J., Vol. 2013. 10.1155/2013/949452

Tabee, E., 2008. Lipid and phytosterol oxidation in vegetable oils and fried potato products. Ph.D. Thesis, Department of Food Science, Faculty of Natural Resources and Agricultural Sciences, Swedish University of Agricultural Sciences, Uppsala, Sweden.

Van der Merwe, G.H., L.M. du Plessis and J.R. Taylor, 2004. Changes in chemical quality indices during long-term storage of palm-olein oil under heated storage and transport-type conditions. J. Sci. Food Agric., 84: 52-58.
CrossRef  |  Direct Link  |  

Wahab, O.M. and Q.C. Elabor, 2016. Variation in the phytochemical constituents of seeds, mature and immature leaves of Moringa oleifera Lam. growing in five local government areas of Oyo State, Nigeria. J. Nat. Sci. Res., 6: 54-60.
Direct Link  |  

Wang, J., D. Wu and W.C. Shen, 2002. Structure-activity relationship of reversibly lipidized peptides: Studies of fatty acid-desmopressin conjugates. Pharmaceut. Res., 19: 609-614.
CrossRef  |  Direct Link  |  

White, P.J., 1995. Conjugated Diene, Anisidine Value and Carbonyl Value Analysis. In: Methods to Access Quality and Stability of Oils and Fat-Containing Foods, Warner, K. and N.A.M. Eskin (Eds.). Chapter 9, AOCS Press, Champaign, IL., USA., ISBN-13: 9780935315585, pp: 159-178.

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