Physicochemical Properties and Antioxidant Activity of Pulsed Electric Field-Treated Baobab Oil

Abstract

This study investigated the impact of pulsed electric field (PEF) pretreatment on the characterisation and antioxidant activity (AA) of baobab seed oil. Prior to extraction, PEF treatments of 1–3 kV/cm at 40–120 pulses and specific energies (SE) of 1.60–43.2 kJ/kg were applied. No differences in oil yield (9.50–11.85%) were observed; however, PEF at a SE of 19.20 kJ/kg produced a higher yield than the control at 9.55% (p < 0.05). PEF did not alter the refractive index, specific density, acid value (AV), free fatty acids, peroxide value (PV), iodine value and fatty acid profile (p > 0.05). The PV was less than the Codex specification (≤15 mEq/kg); however, the AV (5.54–10.50 mg KOH/g) were above the recommended limit of 4 mg KOH/g. The latter is likely attributed to the initial quality of the seeds irrespective of PEF treatment. Regarding antioxidants, DPPH-RS responded to PEF (p < 0.05), with a non-linear trend across treatments. The DPPH-RS of PEF-treated oils ranged from 38.89–76.23%, compared to 49.9% for the control. This demonstrates that PEF preserved the quality of baobab oil, while its effect on AA depended on treatment intensity: lower energy levels enhanced DPPH-RS, whereas higher intensities reduced it.

1. Introduction

As global challenges like climate change and conflict intensify, urbanisation rises, reducing self-sufficiency and increasing dependence on purchased food. To counter these challenges and achieve the Sustainable Development Goals of ‘No Poverty’ and ‘No Hunger,’ new sources of food are being explored, including non-forest plant species such as the drought-tolerant baobab tree. The resilient and nutrient-rich resource, Adansonia digitata L. (a member of the Malvaceae family), is Africa’s oldest and most well-known tree, endemic to the Savannah regions of Africa, and is vital for food security [1,2]. Due to its importance as a source of sustenance, the baobab is often referred to as the “magic tree” or “chemist tree” [3].

The whole baobab tree is useful, including the bark, leaves, and fruit (shell, pulp, and seeds). The tree produces distinctive, globose, hard-shelled fruits with seeds covered in a whitish pulp [4]. While the fruit pulp is used commercially or domestically to thicken various beverages, including smoothies and jams [3,5], the seeds also provide nourishment for a significant number of rural dwellers [6,7]. Traditionally, baobab seeds are consumed raw, roasted, boiled, or crushed into flour as thickeners or flavouring agents in soups and stews [4,7]. Furthermore, the oil extracted from the seed is valuable in traditional medicine, where it is applied to treat oral ailments such as toothaches and gum diseases, and it is also used to cure diarrhoea [5,7]. Due to its properties, the oil is used internationally in the cosmetics industry [8].

Oil production from seeds conventionally relies on methods such as pressing or solvent extraction, which often use high temperatures to maximise yield. However, high temperature can degrade heat-sensitive functional components, such as antioxidants, resulting in a less nutritionally potent product [9,10,11]. This challenge has driven the development of non-thermal extraction techniques, such as ultrasound, which aim to increase efficiency while preserving quality.

Another highly effective non-thermal approach is Pulsed Electric Field (PEF) treatment. PEF involves applying high-voltage electrical pulses to the food product at low temperatures for only a few milliseconds to microseconds. During PEF treatment, the food is placed between two electrodes [11]. PEF induces stress on cells, leading to electroporation, which, depending on the intensity, can cause reversible or irreversible permeabilisation of the cell membrane. Exceeding a critical transmembrane potential lead to the formation of pores in weak regions of the membrane, which subsequently increase permeability [10,11]. Low electric field strengths (e.g., 0.1 to 1 kV/cm) cause reversible permeabilisation, while moderate intensities (1 to 5 kV/cm) can cause irreversible permeabilisation in both plant and animal cells.

PEF is applied across various applications, including cold pasteurisation, texture softening (e.g., in the French fry industry), and enhancing mass transfer for releasing intracellular components from plant cells. PEF pretreatment of oilseeds increases oil extraction efficiency, reducing degradation of heat-sensitive ingredients [12,13].

Studies on several vegetable oils have shown that PEF pretreatment has little or no effect on the physicochemical characteristics of the oils [14,15,16], but substantially enhances yield and antioxidant profile. This is evidenced by the reported increase in virgin olive oil yield, ranging from 3 to 6% [15,16,17]. Regarding compounds with antioxidant activity, Mazroei Seydani et al. [14] reported a significant increase in the phenolic content of rapeseed oil as the PEF electric field increased from 1 to 7 kV/cm; the increase was more pronounced at 80 pulses than at 30 pulses. In another study, PEF treatment at an electric field strength of 1.6 kV/cm and an energy of 4.6 kJ/kg applied to olive paste increased the total phenolic and flavonoid content of the oil by 7.6% and 18.3%, respectively, compared to the control [15]. In the same breath, these authors also reported that PEF increased lipase activity, resulting in a higher acid value. However, in these cases, none of the acid values exceeded the recommended levels.

Although several studies have characterised baobab seed oil and evaluated its physicochemical and antioxidant properties, limited information is available regarding the use of pulsed electric field (PEF) pretreatment prior to oil extraction. Furthermore, no studies were identified during our literature survey that examined the effect of PEF pretreatment on the physicochemical properties and antioxidant activity of baobab seed oil. Therefore, this study aimed to evaluate the effect of PEF pretreatment on the physicochemical properties (yield, lipid characterisation, and colour) and antioxidant activity (DPPH radical scavenging and peroxide value) of the resultant oil from baobab seeds.

2. Materials and Methods

2.1. Baobab Seeds and Reagents

The seeds were obtained from baobab (Adansonia digitata) fruits harvested in the Vhembe Region of Limpopo. 2,2-Diphenyl-1-picrylhydrazyl, ethanol, sodium hydroxide, hydrochloric acid, acetyl chloride, methanol, acetic acid, chloroform, potassium iodide, sodium thiosulfate, hexane, petroleum ether, and iodine monochloride were purchased from Merck (Modderfontein, Johannesburg, South Africa). The chemicals used in this study were of analytical grade, and chemical reagents were prepared according to standard analytical procedures. Prepared reagents were stored under conditions that prevented deterioration or contamination. The water used was purified with the Milli-Q water purification system (Millipore, Microsep, Bellville, Cape Town, South Africa).

2.2. Sample Preparation

Baobab seeds containing some adhering pulp were washed, dried at 65 °C for 24 h, and subsequently milled/ground (Fritsch, Idar-Oberstein, Germany) using a sieve with an aperture of 4.0 mm.

2.3. Pulsed Electric Field Treatment

Pulsed electric field treatment of baobab seeds was performed using the method of Mazroei Seydani et al. [14] with slight modifications. A floor-standing bench PEF system (DIL-Elea, Quakenbrück, Germany) was used, which generates exponentially decaying pulses with a maximum voltage of 30 kV at a pulse frequency of 2 Hz. Ground baobab seeds (100 g) in 300 g of water were placed in the treatment chamber with an electrode gap of 8 cm and exposed to 40–120 pulses at a field strength of 1–3 kV/cm, which resulted in specific energies ranging from 1.60–43.2 kJ/kg (

Table 1. PEF treatment settings applied to the baobab seed samples.

Treatments	Chamber Size	Voltage	Pulses	Field Strength	Specific Energy
	cm	kV	Count	kV/cm	kJ/kg
1	8	8	40	1.00	1.60
2	8	8	80	1.00	3.20
3	8	8	120	1.00	4.80
4	8	16	40	2.00	6.40
5	8	16	80	2.00	12.80
6	8	16	120	2.00	19.20
7	8	24	40	3.00	14.40
8	8	24	80	3.00	28.80
9	8	24	120	3.00	43.20

). The selected PEF parameters were chosen based on ranges previously reported for oilseed processing and extraction studies. Given the lack of published information on PEF-assisted extraction of baobab seed oil, a broad range of treatment intensities (low, moderate, and high) was investigated to evaluate the matrix response and identify conditions that could influence oil yield and quality characteristics. The untreated seed meal (control) was stored in water simultaneously to ensure comparability. The PEF-treated and untreated seeds were freeze-dried (SP Scientific, Warminster, PA, USA).

2.4. Proximal Composition of Baobab Seeds

The proximal composition of PEF-treated and untreated ground baobab seeds, such as moisture content (vacuum oven method 981.05), crude fat (soxtec system 920.85) and crude ash (muffle furnace 920.48), was carried out following AOAC methods [18].

The protein content was measured using the Dumas method with the TruSpec N (Leco Corporation, St. Joseph, MI, USA). The protein content was calculated using the nitrogen content and the conversion factor of 6.25 [7]. The carbohydrate content was determined by difference, accounting for the contributions of ash, moisture, crude fat, and protein.

2.5. Extraction of Fat

The oil from the PEF-treated and untreated control samples was extracted immediately after drying, following the modified methods of Abeer et al. [19] and Cissé et al. [9]. The ground baobab seeds (40 g) and n-hexane were mixed in a 1:9 (mass/volume) ratio in an Erlenmeyer flask (500 mL) and stirred continuously on a heating block with a magnetic stirrer at 1500 rpm for 6 h at 40 °C. The Erlenmeyer flasks were covered throughout the experiment to prevent the hexane from evaporating. The oil-hexane mixtures were centrifuged for 15 min at 10,000 rpm (Beckman Coulter, Limerick, Ireland) to remove the impurities. The oil-hexane mixture was kept overnight under a fume hood to allow the residual hexane to evaporate. The hexane-free oil was stored in the ultra-freezer at −80 °C until analysis.

2.5.1. Characterisation of the Oil

The oil extraction efficiency, reported as a percentage, was determined as the weight of the obtained oil divided by the weight of the primary ground seeds, multiplied by 100 [20]. Physicochemical properties, including acid value (969.17), iodine value (920.159), free fatty acids (940.28), peroxide value (965.33), saponification value (920.160), melting (920.157), freezing point (929.08), refractive index (921.08) and density, were determined by the AOAC methods [18].

The colour of the PEF-treated and untreated baobab seed oils was measured according to the modified method of Maraulo et al. [21]. The CIELab parameters L* (brightness, 100 = white, 0 = black), a* (+red; −green) and b* (+yellow; −blue) were measured with a spectrophotometer (CM-5, Konika Minolta, Japan) using a D65 daylight source, a large viewing area and an observer angle of 10°. Measurements were performed in triplicate, and the system reported the average.

2.5.2. The Fatty Acid Profile

Fatty acid composition of baobab oil was determined according to a modified method of Msalilwa et al. [6]. Fatty acid methyl esters (FAMEs) were prepared from the extracted oil samples following the AOAC Official Method 996.06 [18]. Briefly, 50 mg of oil sample was weighed into a 50 mL glass reaction tube and mixed with 3 mL of 0.5 M methanolic sodium hydroxide. The mixture was refluxed for 10 min, after which 3 mL of acetyl chloride was added, and the refluxing was continued for a further 10 min. The reaction mixture was then cooled to room temperature before adding 8 mL of hexane and 10 mL of distilled water. The mixture was allowed to stand for 5 min to facilitate phase separation. The upper hexane layer containing the FAMEs was collected and transferred into GC vials for analysis. Fatty acid methyl esters were analysed using an Agilent 6890 gas chromatograph coupled to a 5973 MS/FID system (Agilent Technologies, Santa Clara, CA, USA). Separation was achieved on an HP-88 fused silica capillary column (100 m × 0.25 mm i.d., 0.20 μm film thickness; Agilent Technologies). Nitrogen was used as the carrier gas at a constant flow rate of 1.0 mL/min. Samples (1 μL) were injected in split mode with a split ratio of 50:1. The injector and detector temperatures were maintained at 250 °C. The oven temperature programme was set at an initial temperature of 50 °C and held for 2 min, followed by heating at 5 °C/min to 250 °C and holding for 15 min.

Fatty acids were identified by comparing retention times with those of fatty acid methyl ester standards analysed under the same chromatographic conditions in accordance with AOAC Official Method 996.06 [18]. Quantification was performed using the FAME100M calibration method, and the relative concentration of each fatty acid was calculated by peak area normalisation and expressed as a percentage of the total identified fatty acids.

2.5.3. Antioxidant Activity via the DPPH Radical Scavenging Activity

The 1,1-diphenyl-2-picryl-hydrazyl radical scavenging (DPPH-RS) activity procedure was initiated by 0.4 mL of oil samples with 2 mL of DPPH (0.12 mM) in absolute ethanol. The reaction mixture was incubated for 30 min in the dark, and then the absorbance of the resulting solutions was measured at 517 nm using a spectrophotometer (Lambda 25, Perkin Elmer, Singapore, Singapore). The control was prepared similarly, except that ethanol was used [22]. The percentage of inhibition was calculated using the formula:

% DPPH−RS = [(A₀ − A₁)/A₀] × 100

where: A₀ is the absorbance of the control, and A₁ is the absorbance of the oil test sample at 517 nm.

2.6. Statistical Analysis

Statistical analysis was performed using SPSS 29.0 for Windows^®. Analysis of variance (ANOVA) established the significance of each dependent factor. Descriptive statistical analyses determined the triplicate’s mean and standard deviation (n = 3). Duncan’s multiple-range tests indicated significant differences among the means. The level of confidence required for significance was selected at 95%.

3. Results and Discussion

3.1. Baobab Seeds Composition

Table 2. Proximal composition of pulsed electric field-treated baobab seeds.

Sample	Proximal Composition (%)
SE (kJ/kg)	MC	CA	P	C	F
Control	4.34 ± 0.12 ab	4.54 ± 0.26 a	17.98 ± 3.10 ab	41.34 ± 4.42 a	22.19 ± 0.00 a
1.60	5.82 ± 0.94 cd	4.39 ± 0.06 a	21.91 ± 3.12 b	35.74 ± 1.34 a	23.07 ± 0.00 a
3.20	6.91 ± 0.55 d	4.24 ± 0.62 a	17.03 ± 2.17 ab	40.08 ± 2.98 a	22.18 ± 0.00 a
4.80	6.82 ± 0.35 d	4.20 ± 0.33 a	17.33 ± 2.95 ab	41.93 ± 1.93 a	22.61 ± 0.00 a
6.40	6.09 ± 0.66 d	4.38 ± 0.16 a	21.10 ± 1.77 ab	35.42 ± 4.26 a	22.44 ± 0.00 a
12.80	4.88 ± 0.72 bc	4.39 ± 0.23 a	19.78 ± 3.53 ab	37.86 ± 3.67 a	23.32 ± 0.00 a
19.20	3.84 ± 0.51 ab	4.56 ± 0.34 a	18.46 ± 2.18 ab	38.77 ± 2.5 a	22.18 ± 0.00 a
14.40	4.13 ± 0.02 ab	4.10 ± 0.07 a	19.21 ± 1.46 ab	40.27 ± 1.12 a	22.28 ± 0.00 a
28.80	3.46 ± 0.24 a	4.18 ± 0.07 a	18.05 ± 4.48 ab	41.61 ± 6.59 a	22.45 ± 0.00 a
43.20	4.34 ± 1.16 ab	4.42 ± 0.39 a	16.40 ± 1.37 a	41.52 ± 3.69 a	22.29 ± 0.00 a

SE-specific energy. Data presented as mean ± standard deviation (n = 3) of MC-moisture content, CA-crude ash, P-protein, C-carbohydrates and F-fibre of PEF-treated baobab seeds. ANOVA and Duncan’s multiple-range tests were performed. ^a–d Means with different letter superscripts in the same column denote significant differences (p < 0.05).

depicts the proximal composition of PEF-treated baobab seeds. The proximal composition of PEF-treated ground baobab reported was within the range of those reported in the literature for Adansonia digitata. Values of 4.1–4.56% for crude ash, protein 16.4–21.91%, carbohydrates 35.42–41.93%, fibre 22.19–23.32%, and moisture content 3.46–6.91% were similar to those reported by Asogwa et al. [3], Dhlakama et al. [4] and Muthai et al. [7]; with authors such as Asogwa et al. [3] and Wapwera & Egila [23] reporting lower and higher values than the above. In terms of the effect of PEF treatment, no significant differences (p > 0.05) were reported for crude ash, protein, carbohydrates and fibre of all ground baobab seeds. This might be attributed to the total measurement, rather than the extraction of those components from the seeds. Even if PEF can help release these from sources, they still remain in the system for analysis. The effect of PEF on moisture content (MC) varied with treatment parameters. Regarding the MC, samples treated at specific energy (SE) of 12.80–43.20 showed no significant differences (p > 0.05) from the control; however, SE of 1.60–6.40 exhibited significantly higher (p < 0.05) MC than the control. The higher moisture content observed at lower PEF energy levels may be related to a lower degree of cellular disruption, resulting in reduced mass transfer and less efficient moisture removal during subsequent freeze-drying. Since PEF treatment was performed in an aqueous medium, increasing energy inputs may have promoted greater cellular permeabilisation, facilitating moisture migration and sublimation during drying. However, the mechanisms responsible for the observed differences in moisture content cannot be conclusively established from the present data, as no direct microstructural analyses were performed. Further studies employing techniques such as scanning electron microscopy or cryo-SEM would be valuable for elucidating the structural changes induced by PEF treatment and their influence on drying behaviours [12]. Of importance to this study is the effect of PEF on the yield of the fat; results thereof will be depicted in

Table 3. Physicochemical properties of PEF-assisted extracts of baobab seed oil.

SE	OY	SD	RI
kJ/kg	(%)	(g/cm)
Control	9.55 ± 1.26 a	0.8960 ± 0.00 c	1.4693 ± 0.00 a
1.60	9.50 ± 0.21 a	0.9100 ± 0.00 d	1.4689 ± 0.00 a
3.20	9.55 ± 0.59 a	0.8803 ± 0.00 b	1.4681 ± 0.00 a
4.80	10.2 ± 1.47 ab	0.8910 ± 0.00 c	1.4680 ± 0.00 a
6.40	10.48 ± 0.26 ab	0.9141 ± 0.00 d	1.4684 ± 0.00 a
12.80	10.50 ± 1.64 ab	0.8710 ± 0.00 ab	1.4684 ± 0.00 a
19.20	11.85 ± 1.33 b	0.8803 ± 0.00 b	1.4692 ± 0.00 a
14.40	10.48 ± 0.45 ab	0.8641 ± 0.00 a	1.4696 ± 0.00 a
28.80	10.52 ± 1.93 ab	0.9100 ± 0.01 d	1.4693 ± 0.00 a
43.20	10.76 ± 0.45 ab	0.8803 ± 0.00 b	1.4693 ± 0.00 a

SE-specific energy. Data presented as mean ± standard deviation (n = 3) of OY-oil yield, SD-specific density and RI-refractive index of PEF-assisted extraction of baobab oil. ANOVA and Duncan’s multiple-range tests were performed. ^a–d Means with different letter superscripts in the same column denote significant differences (p < 0.05).

. A study aimed at assessing the effect of PEF treatment on olive oil extraction reported no significant differences in the MC of dried olive pomace treated at specific energies of 3.2 and 5.1 kJ/kg compared with the control, in agreement with the results of the present study.

3.2. Physicochemical Properties of the Seed Oil

The fat content and quality of baobab seeds are important, as these oils are valuable in the cosmetic industry [8]. The fat content of 9.55–11.85% reported in the present study (Table 3) falls within the low range of the spectrum compared to other studies, where values between 11.20% and 29.6% were reported [1,3,23]. Variations in seed composition are influenced by factors such as regional climate and soil type, as noted by Schulte et al. [24]. It should also be noted that the baobab seeds used in this study originated from a single geographical region and harvest batch; the findings may not fully capture the natural variability associated with different populations, growing environments, seasons, and genetic diversity of baobab trees. Nevertheless, using a single seed source reduced variability arising from raw material differences, thereby enabling a more focused evaluation of the effects of pulsed electric field pretreatment on the physicochemical and antioxidant properties of baobab seed oil.

Although the treatment corresponding to a specific energy input of 19.20 kJ/kg produced a significantly higher yield than the control, no consistent increase in oil yield was observed across the PEF treatments, as seen in Table 3. Therefore, the overall findings suggest that PEF had a limited effect on baobab oil extraction under the investigated conditions. Nevertheless, the response observed at 19.20 kJ/kg indicates a potential treatment optimum that should be explored in future optimisation studies. Nevertheless, our results are similar to those reported by Tamborrino et al. [17], who found that PEF treatment of olive pomace before extraction at SE of 3.1 kJ/kg did not have a significant effect on enhancing oil extraction compared to the control; however, at SE 5.1 kJ/kg, oil extraction was improved by 5.64%. Leone et al. [16] also reported a 3.18% increase in oil extraction at 4 kJ/kg compared to the untreated olive pomace.

The physical properties of oil, such as refractive index (RI) and specific density (SD), are crucial for identifying and assessing its quality. Both RI and SG can be used to monitor degradation, such as oxidation and hydrolysis. The RI value is based on the high levels of fatty acid unsaturation. As a result, baobab oil is categorised as a non-drying oil [8]. The RI was reported to range from 1.4680–1.4696 (Table 3), and PEF treatment had no significant effect on the RI (p > 0.05). Our observed values are similar to those reported at 1.425–1.431 [2], 1.436 [19], 1.4666 [8] and 1.498 [25]. However, lower values of 1.04–1.05 were also reported [6].

Regarding SG, the observed values ranged from 0.8641 to 0.9141 g/cm³. Although slight significant differences were observed between PEF-treated and the control, the observed values are within the range reported in the literature for baobab oils: 0.869–0.928 g/cm³ [6,8,19,25].

3.3. Chemical Properties

The chemical properties of PEF-treated oils are depicted in

Table 4. Chemical properties of PEF-assisted extracts of baobab seed oil.

SE	pH	AV	FFA	IV	PV
kJ/kg		(mgKOH/g)	(%)	(gI2/100 g)	(mEq/kg)
Control	5.61 ± 0.01 j	7.43 ± 3.48 a	3.73 ±1.75 a	72.60 ± 0.01 i	4.93 ± 1.35 abc
1.60	4.81 ± 0.00 f	7.73 ± 4.93 a	3.88 ± 2.47 a	73.48 ± 0.00 j	4.59 ± 0.66 abc
3.20	4.89 ± 0.00 g	10.43 ± 3.60 a	5.24 ± 1.81 a	64.11 ± 0.00 f	5.19 ± 0.92 abc
4.80	4.65 ± 0.00 d	5.54 ± 0.04 a	2.79 ± 0.01 a	57.67 ± 0.00 c	3.67 ± 0.95 ab
6.40	4.67 ± 0.00 e	6.40 ± 2.12 a	3.22 ± 1.07 a	54.16 ± 0.00 a	6.22 ± 0.73 c
12.80	4.63 ± 0.00 c	10.43 ± 3.61 a	5.24 ± 1.81 a	55.33 ± 0.02 b	3.50 ± 1.21 a
19.20	4.47 ± 000 a	9.77 ± 1.51 a	4.91 ± 0.76 a	62.64 ± 0.00 d	5.50 ± 1.77 abc
14.40	4.56 ± 0.00 b	9.81 ± 1.40 a	4.93 ± 0.70 a	63.21 ± 0.01 e	5.84 ± 0.86 bc
28.80	5.04 ± 0.00 i	7.03 ± 4.28 a	3.53 ± 2.14 a	65.87 ± 0.00 g	5.67 ± 1.53 abc
43.20	5.03 ± 0.00 h	10.50 ± 0.70 a	5.28 ± 0.35 a	67.04 ± 0.00 h	6.13 ± 1.3 c

SE-specific energy. Data presented as mean ± standard deviation (n = 3) of pH, AV-acid value, FFA-free fatty acid, IV-iodine and PV-peroxide value of PEF-assisted baobab oil. ANOVA and Duncan’s multiple-range tests were performed. ^a–j Means with different letter superscripts in the same column denote significant differences (p < 0.05).

. The pH values of the baobab oil samples ranged from 4.47 to 5.61 and differed significantly for all samples, with the control exhibiting the highest pH at 5.61. Ibrahim & Yassin [8] and Oyeleke et al. [25] reported pH values of 6.12 and 6.2 for baobab oil, respectively, in the slightly acidic range. Within PEF-treated samples, no specific pattern was observed across treatments. However, the lowest pH values were observed in the order of intermediate (12.8–19.2 kJ/kg), low (1.6–6.4 kJ/kg), and high (28.8–43.2 kJ/kg) intensity PEF. The pH of oil depends on its free fatty acid (FFA) content. The more triglycerides are hydrolysed by inherent lipase activity, the more FFA are produced, thus lowering pH. PEF has been reported to increase the acidity of olive oil by increasing the extraction of phenolic acids and accelerating lipase-catalysed hydrolysis, thereby increasing the acid content and affecting the pH [15].

The acid value of 5.54–10.50 mg KOH/g and the free fatty acid (FFA) of 2.79–5.28% are depicted in Table 4. Applying PEF treatment did not affect the AV and FFA of baobab oil (p > 0.05). Authors who characterised baobab oil reported AV of 0.43, 5.8, 6.52, and 6.8 [2,8,19,25] and FFA of 1.03–1.06 KOH/g [6], with the latter lower compared to values reported in this study.

However, a study by Ofori et al. [2] reported an AV of 9.31 for screw-pressed baobab oil, compared with 4.57 mg KOH/g for Soxhlet-extracted baobab oil. This indicated that the characterisation of oils can also be influenced by preparation methods other than their natural composition. Moreover, our AV values and those reported in the literature exceed the 4 mg KOH/g threshold set for virgin and cold-pressed oils and fats [26] (Codex Alimentarius Commission, 1999). A high acid and free fatty acid is an indication of hydrolysis. In the present study, PEF did not significantly affect AV or FFA. Our results are in accordance with Leone et al. [16] and Tamborrino et al. [17], who reported no significant increases in FFA of extra virgin olive oil. Leone et al. [16] recorded 0.24 and 0.25% for the control and PEF treated (2.4 kV/cm at a specific energy of 4 kJ/kg), meanwhile, values of 0.24, 0.23 and 0.24% were reported for the control, 3.2 kJ/kg and 5.1 kJ/kg [17]. However, contrary to the afore-mentioned results of our study, Yang et al. [15] reported a 12.5% increase in acid value of virgin olive oil at an energy input of 4.6 kJ/kg and an electric field strength of 1.6 kV/cm. In another study, rapeseed oil treated at 0–7 kV/cm with 30 and 80 pulses showed an increase in AV as the electric field strength and the number of pulses increased [14]. Both authors attributed the increase in AV to electroporation-induced lipase activity, leading to hydrolysis and the formation of FFA. It should be noted that in this study, we reported high AV and FFA for both PEF-treated and control samples; the elevated AV and FFA content may suggest that partial hydrolysis occurred prior to treatment, extraction and analysis. Such hydrolysis could be associated with endogenous lipase activity influenced by storage and handling conditions. However, the specific cause could not be determined within the scope of the present study.

The iodine value (IV) of an oil or fat indicates its level of unsaturation. The iodine value of PEF-treated baobab seed oils was reported at 54.16–73.48 gI₂/100 g as shown in Table 4. The highest values reported for the control and treatment at SE 1.6 at 72.6 and 73.48 gI₂/100 g, respectively. Based on our results and those reported by the afore-mentioned authors, baobab oil is classified as low in unsaturated fatty acids and non-drying. The IV of baobab oil was reported within the range (56 to 98.30 gI₂/100 g) by several researchers for baobab oil [1,6,8,19,25,27]. With IV reported by Ghislain et al. [1] and Abubakar and Afolayan [27] closely resembling the lower spectrum of our range at 53.35 and 54.41 gI₂/100 g, respectively. These authors applied hexane extraction conditions similar to ours. Variations in seed composition are influenced by factors such as regional climate, soil type, genotype, growing conditions, and harvesting season. The wide range of values reported for baobab oil in the literature may therefore be attributed to differences in geographical origin, environmental conditions, and extraction methods. Testament to this, referenced studies were conducted in Nigeria, Sudan, Cameroon, and Tanzania, with the latter country comparing baobab oils from three different regions. These studies employed both cold pressing and solvent extraction methods. Evidently, the IV of hexane-extracted hulled rapeseed oil (106 gI₂/100 g) was significantly lower than that of pressed oil (116 gI₂/100 g). Cissé et al. [9] reported the highest IV for pressed baobab oil (99.11 gI₂/100 g) compared to 56.27, 83.30 and 90.78 gI₂/100 g for chloroform, acetone and hexane, respectively. However, Ofori et al. [2] reported a contradiction: they did not observe any significant differences (p > 0.05) in the IV of mechanical and Soxhlet extraction of baobab oil at 85.89 and 88.45 gI₂/100 g⁻¹, respectively. The low IV values reported for solvent extraction may be due to the prolonged exposure to oxygen during extraction and solvent evaporation, which can lead to oxidation and lower unsaturation levels.

Regarding the effect of PEF, the IV of the control did not differ (p > 0.05) from that of the lowest SE (1.6 kJ/kg) at 72.60 and 73.4 gI₂/100 g, respectively. However, as the PEF intensity increased to 6.4 kJ/kg, a decrease in IV (73.4–54.16 gI₂/100 g) was reported (p < 0.05), followed by an increase (55.33–67.04 gI₂/100 g) from 12.8 to 43.2 kJ/kg (p < 0.05). However, most researchers reported no significant effect of PEF on fat characterisation (IV, saponification, AV, RI, density). A study involving PEF treatment of cannabis oil at electric field strengths of 0, 3 and 6 kV/cm revealed that the IV correlated negatively with electric field strength. The lowest IV was reported in cannabis oil exposed to medium PEF intensity (3 kV/cm). Their results are similar to those of the current study, in which intermediate PEF intensities at SE of 6.4 to 12.80 kJ/kg exhibited the lowest IV of 54.16–55.33 gI₂/100 g⁻¹. Moreover, they also reported that the AV of the cannabis oil was unaffected, similar to the present study [20].

The PV of PEF-treated baobab oil is presented in Table 4. No significant differences in PV were observed among samples (p > 0.05); thus, PEF did not affect PV. The average PV was 5 mEq/kg, which is a third of the limit set for cold-pressed and virgin oils at 15 mEq/kg [28] (Codex Alimentarius Commission, 1989). Research on baobab oil reported values ranging from 3.2 to 21.73 mEq/kg. Most Authors who reported low PV values ≤15 mEq/kg, also reported an AV of ≤4 [8,19,27], and vice versa [1], except Cissé et al. [9] who reported a PV of ≤3 mEq/kg, but had AV above the recommended levels ranging from of 5.57–18.83 mg KOH/g for oils extracted using pressing and different solvents. Their results are similar to ours: a high AV and a low PV.

To further explain the non-significant effect of PEF treatment on PV, the results of Leone et al. [16] and Tamborrino et al. [17] on extra-virgin olive oil were consistent with the present study. Leone et al. [16] reported no significant changes in PV (5.85 ± 0.93 and 5.68 ± 0.93) for PEF-treated oil (4 kJ/kg), while Tamborrino et al. [17] varied the SE from 3.2–5.1 kJ/kg and obtained PV of 6.4–7.6 mEq/kg. However, Yang et al. [15] reported a 4.49% increase in PV and a 12% increase in AV in virgin olive oil treated with 4.6 kJ/kg and 1.6 kV/cm. Nonetheless, these increases were well below the limits set for olive oil, with AV of 6.6 mg KOH/g and PV of 20 mEq/kg [28].

3.4. Fatty Acid Composition

The fatty acid (FA) composition of PEF-treated baobab oil ranged from 38.01–43.03%, 31.37–39.30%, 18.09–21.21%, for the major FAs: oleic, linoleic and palmitic acid, respectively (

Table 5. Fatty acid composition of PEF-assisted extracts of baobab seed oil.

Sample	Major Fatty Acids (%)			Minor Fatty Acids (%)
SE	O	L	P	S	A	M	E	AL
kJ.kg−1	C18:1	C18:2	C16:0	C18:0	C20:0	C14:0	C20:1	C18:3
Control	41.10 ± 1.80 cde	32.14 ± 1.41 a	18.26 ± 0.80 a	2.18 ± 0.11 a	1.32 ± 0.11 bc	0.29 ± 0.06 ab	0.39 ± 0.02 c	0.14 ± 0.02 bc
1.60	39.35 ± 1.80 abc	33.06 ± 1.48 abc	18.71 ± 0.84 a	2.76 ± 0.41 a	1.29 ± 0.06 bc	0.22 ± 0.66 a	0.36 ± 0.02 bc	0.16 ± 0.04 bc
3.20	38.01 ± 0.57 a	34.43 ± 0.57 bc	21.12 ± 7.39 a	2.93 ± 0.92 ab	0.89 ± 0.08 a	0.32 ± 0.92 bc	0.26 ± 0.20 ab	0.21 ± 0.16 c
4.80	40.47 ± 0.47 bcd	34.70 ± 0.76 c	19.73 ± 0.48 a	2.60 ± 0.01 a	1.49 ± 0.11 bc	0.22 ± 0.95 a	0.43 ± 0.00 c	0.08 ± 0.05 ab
6.40	41.18 ± 0.56 cde	32.95 ± 0.46 abc	19.20 ± 0.49 a	2.83 ± 0.08 a	1.30 ± 0.03 bc	0.25 ± 0.73 ab	0.43 ± 0.20 c	0.20 ± 0.03 c
12.80	38.35 ± 2.52 ab	32.56 ± 2.08 ab	18.61 ± 1.22 a	2.25 ± 0.20 a	1.75 ± 0.62 d	0.20 ± 1.21 a	0.38 ± 0.02 c	0.14 ± 0.03 bc
19.20	38.43 ± 1.19 ab	39.30 ± 0.54 d	18.14 ± 8.34 a	2.29 ± 1.05 a	0.95 ± 0.10 a	0.36 ± 1.77 b	0.22 ± 0.10 a	0.12 ± 0.07 abc
14.40	43.03 ± 0.57 e	31.88 ± 2.17 a	21.21 ± 0.12 a	3.82 ± 1.18 b	1.33 ± 0.01 bc	0.28 ± 0.86 bc	0.43 ± 0.00 c	0.14 ± 0.03 bc
28.80	42.11 ± 2.68 de	31.37 ± 1.26 a	18.09 ± 0.59 a	2.96 ± 0.34 ab	1.08 ± 0.09 ab	0.26 ± 1.53 ab	0.46 ± 0.03 c	0.03 ± 0.03 a
43.20	42.23 ± 0.35 de	33.41 ± 0.40 abc	18.80 ± 0.4 a	2.76 ± 0.15 a	1.05 ± 0.04 ab	0.27 ± 1.3 ab	0.37 ± 0.01 bc	0.06 ± 0.00 ab

SE-specific energy. Data presented as mean ± standard deviation (n = 3) of fatty acid composition of PEF-assisted extraction of baobab oil. O-oleic acid; L-linoleic; P-palmitic, S-stearic; A-arachidic; M-myristic; E-eicosanoic and AL-alpha linolenic acid. ANOVA and Duncan’s multiple-range tests were performed. ^a–e Means with different letter superscripts in the same column denote significant differences (p < 0.05).

). The minor FA content decreased in the order from stearic, arachidic, eicosanoic, myristic, to linolenic acid (Table 5). The FA reported in our study is within the ranges reported by several authors for baobab oil. These are oleic 32.09–42.51%, linoleic 19.62–28.15% and palmitic 14.95–22.32% [7,19,29]. PEF pretreatment of baobab seeds did not affect the FA composition of the oil, with a few outliers. For instance, oil with an SE of 19.20 kJ/kg exhibited the highest linoleic acid content.

The fatty acid content and profiles of olive treated at 2.4 kV/cm; 4 kJ/kg 6 µs pulse width [16], rapeseed (0, 1, 4, and 7 kV/cm) with 30 and 80 pulse numbers and pulse width of 20 μs [14] remained unchanged following PEF pretreatment. Although these parameters were not evaluated in the present study, previous studies on other oil matrices have shown that PEF may influence minor bioactive constituents and oxidative stability. For example, Leone et al. [16] reported increases in decarboxymethyl oleuropein-aglycone di-aldehyde (14%), oleuropein derivatives (11%), and total hydrophilic phenols (9%), while Mazroei Seydani et al. [14] observed increases in carotenoid (2–16%), chlorophyll (0.3–23%), and total phenol (43–70%) content. These changes were associated with improved oxidative stability. Such findings suggest that future studies should investigate whether similar effects occur in PEF-treated baobab oil.

However, contradictory results to the above: studies on the effect of PEF (50 kJ/kg) on oil obtained from the valorisation of five different berry seeds reported an increase in saturated fatty acid content and a decrease in unsaturated fatty acid content. However, those noted changes were insufficient to affect the overall chemical characteristics of the oils. The authors also attributed the decrease in MUFA and PUFA to possible oxidation induced by higher temperatures [30]. Although the extraction temperature was not specified, it may have increased due to the high specific energy of 50 kJ/kg. In another study, the combination pretreatment of Niger seed oils with microwave (900 W; 0–200 s) and PEF (0–5 kV/cm, with a 30-pulse width of 20 microseconds) resulted in a significant reduction in unsaturated fatty acids and an increase in the content of saturated fatty acids. They attributed these changes to the susceptibility of unsaturated fatty acids to high temperatures during microwave treatment and heat generated by high screw press speeds during extraction [31]. However, this study did not evaluate the effect of PEF alone.

3.5. Antioxidant Activity via DPPH Radical Scavenging Activity (DPPH-RS)

The DPPH-RS of methanol, acetone, and aqueous extracts of baobab seeds is well documented [4,29,32,33]. The DPPH-RS of baobab seeds is attributed to a range of compounds, including ascorbic acid, polyphenols (such as phenolic acids and flavonoids), and tocopherols, among others. Baobab seeds were reported to contain 668.97 mg GAE/100 g DW of total soluble phenolics. The detected phenols were cinnamic (72.44 mg/100 g DW), caffeic (9.09 mg/100 g DW), quercetin (27.82 mg/100 g DW), and catechin (19.09 mg/100 g DW) [29]. Dhlakama et al. [4] reported total phenolic and flavonoid contents of 450 mg GAE/100 g and 780 mg TE/100 g in baobab seeds, respectively. DPPH-RS of 60% was reported for 200 µg/mL methanolic extracts of baobab seeds [1]. It can be noted that baobab seeds contain a range of hydrophilic and lipophilic antioxidants. Whole seeds are characterised by hydrophilic compounds such as phenolic acids, flavonoids, and tannins. Therefore, baobab oil contains mainly a lipophilic antioxidant fraction, comprising tocopherols, phytosterols, and lipid-soluble phenolics. Although these chemicals contribute to antioxidant action, their overall concentration is lower than in the whole seed. As a result, baobab seed extracts often exhibit stronger DPPH radical-scavenging activity than the oil [34].

There are numerous reports on the DPPH-RS of baobab oil [9,34,35,36]. Cisse et al. [9] reported on the effect of pressing vs solvent extraction on the DPPH-RS of baobab oil. These authors reported that DPPH-RS decreased to 32%, 26%, 25%, and 9% for pressing, acetone, hexane, and chloroform, respectively. Thompson et al. [34] reported an IC₅₀ of 1617 mg/L for baobab oil, which was 13% lower than the seed extract’s IC_{50 of} 1402.05 mg/L. These findings reiterate our statement mentioned above. In another study, Hussein & Mohammed Hamad [36] reported a DPPH-RS value of 19% for hexane-extracted baobab oil. Of importance is the result reported for hexane extraction, since we also used the same solvent. The values of 19–26% are still lower than the 49.9% in our control sample. However, values ranging from 86.13 to 92.3% were reported for baobab oil, with concentrations of 0.12 to 10 mg/mL [35]. It should be noted that Cisse used 0.1 mM DPPH in methanol, which is similar to the 0.12 mM used in our study in ethanol. The lower 19% reported by Hussein & Mohammed Hamad [36] can also be attributed to their DPPH being three times as concentrated at 300 µM. Higher concentrations of DPPH have been reported to increase the IC₅₀ or decrease the percentage of radical scavenging in samples [37,38]. The marked difference in DPPH radical-scavenging activity between Nigerian baobab oil (30% inhibition at 0.25 mg/mL) [27] and Cameroonian baobab oil (60% inhibition at 0.20 mg/mL) [1] is evident despite the minimal difference in sample concentration, which further confirms the variability in the antioxidant potential of baobab oils. This variability is evidently due to factors such as geographical origin, post-harvest or extraction practices, and oil DPPH concentration in the assay.

Numerous authors reported on varying effects of PEF pretreatment on the DPPH-RS capacity of oil. For virgin olive oil, PEF treatment at 4.6 kJ/kg and field strength of 1.6 kV/cm significantly enhanced its ability to scavenge DPPH free radicals, resulting in a 30.0% increase in antioxidant activity [15]. In rapeseed oil, PEF treatment increased DPPH-RS by approximately 12% compared to the untreated control, although no apparent effect was observed at specific energies of 21.4 and 84 kJ/kg. Notably, PEF induced a substantial increase in total phenolic content in rapeseed oil by 64% and 72% at these respective energy levels [10]. In contrast, pecan nut oil showed no significant differences in DPPH-RS or phytosterol content across treatments ranging from 0.8 to 15 kJ/kg, with values around 46–49 mg TE/100 g [39]. These results suggest that while PEF can enhance antioxidant capacity associated with phenolic content in some oils, such as virgin olive and rapeseed oil, the effect may be limited or absent in others, such as pecan nut oil, possibly reflecting differences in their phytosterol composition and their correlation with DPPH-RS. In addition, the above-mentioned researchers who reported on the DPPH-RS of baobab oil correlated their results with phenolic compounds and other antioxidant assays such as FRAP, TAC or ABTS.

The DPPH-RS of PEF-assisted baobab oil is shown in

Table 6. Antioxidant activity of PEF-assisted extracts of baobab seed oil.

Sample	Antioxidant Activity
SE (Kj/kg)	DPPH-RS
Control	49.90 ± 0.01 c
1.60	66.07 ± 0.01 i
3.20	49.37 ± 0.01 b
4.80	76.23 ± 0.00 j
6.40	57.76 ± 0.01 f
12.80	57.72 ± 0.00 e
19.20	63.46 ± 0.01 h
14.40	52.15 ± 0.00 d
28.80	57.89 ± 0.00 g
43.20	38.89 ± 0.01 a

SE-specific energy, DPPH-RS-1,1-diphenyl-2-picryl-hydrazyl radical scavenging. Data presented as mean ± standard deviation (n = 3) of DPPH-RS of PEF-assisted extraction of baobab oil. ANOVA and Duncan’s multiple-range tests were performed. ^a–j Means with different letter superscripts in the same column denote significant differences (p < 0.05).

. The DPPH-RS activity of baobab oil exhibited a non-linear and statistically significant (p < 0.05) response to varying PEF specific energy levels, as indicated by the Duncan superscripts, which show that all treatments differ. This illustrates how each PEF intensity has a distinct impact on the oil’s antioxidant capacity. There was a significant difference (p < 0.05) between the DPPH-RS of all PEF-treated baobab oils (38.89–76.23%) and the control (49.9%). Some PEF treatments showed lower scavenging activity than the control. The lowest and highest DPPH-RS were reported for the samples treated at specific energies of 43.2 and 3.20 kJ/kg, respectively.

The highest DPPH-RS was observed at 4.8 kJ/kg (76.23%), followed by 1.6 kJ/kg (66.07%) and 19.2 kJ/kg (63.46%). Moderate antioxidant activity was observed at 6.4, 12.8, and 28.8 kJ/kg, with values of approximately 57%, while 14.4 kJ/kg resulted in a slightly lower activity of 52%. The control sample showed 49%, which was comparable only to the 4 kJ/kg treatment. The lowest DPPH-RS value was obtained at 43.2 kJ/kg (38.89%), indicating a decline in radical-scavenging activity at very high PEF intensity.

The observed trend suggests that PEF intensity significantly affects the antioxidant capacity of baobab oil. Compared with the control, low-energy treatments (2–5 kJ/kg) significantly increased DPPH-RS. Mild electroporation, which enhances membrane permeability and facilitates the release of phenolic compounds, tocopherols, and other antioxidants, is responsible for this improvement. Moderate improvements were observed at mid-range intensities (8–30 kJ/kg), indicating partial cell rupture and moderate release of antioxidant constituents.

In contrast, the rapid reduction in activity at 45 kJ/kg suggests that high PEF energy may accelerate the degradation of sensitive bioactive molecules or induce oxidative alterations, thereby diminishing antioxidant potential. Although PEF is considered a non-thermal technique, high specific energy inputs can nonetheless create localised temperature rises and reactive species that contribute to antioxidant depletion. Previous research has shown similar non-linear responses to PEF intensity, supporting the notion that PEF’s positive effects are intensity-dependent.

4. Conclusions

This study demonstrated that PEF pretreatment did not affect the physicochemical properties and fatty acid composition of baobab oil. Key quality parameters remained unaffected, while oil yield showed minor variation; only the 19.20 kJ/kg treatment resulted in a significantly higher yield than the control.

In contrast to the physicochemical properties, antioxidant activity was significantly influenced by PEF pretreatment, with responses varying according to treatment intensity. At the highest treatment level of 43.20 kj/kg, DPPH-RS activity decreased significantly to 38.89%, which was lower than that of the control. Lower energy inputs, particularly 1.60 and 4.8 kJ/kg, enhanced DPPH-RS, whereas higher intensities, such as 43.20 kJ/kg, resulted in reduced activity. These findings suggest that PEF may facilitate the release or extraction of antioxidant constituents while maintaining overall oil quality when appropriately optimised. Overall, PEF preserved the physicochemical and nutritional quality of the oil while showing potential to enhance its functional antioxidant properties, highlighting its value in baobab seed oil processing.

Future studies should incorporate optimisation and additional antioxidant assays and bioactive compound analyses to provide a more comprehensive assessment of the effects of PEF on oil quality and stability.