Determination of minor components and oxidative indices of small-scale pressed sunflower oil during storage

Abstract

Oxidation is the main chemical reaction responsible for the deterioration of oil quality. However, the information available on the subject matter does not indicate the extent to which sunflower oil from poor quality-controlled small-scale processing plants deteriorates under different storage conditions. This study aimed to determine the contents of natural antioxidants and trace metals in crude sunflower oil and monitor the biweekly oxidation indices of samples stored in light and dark for three months. The average α-tocopherol concentration, 170.62 mg/kg, was lower than the recommended concentration (403–935 mg/kg), whereas those of β-carotene and total phenols were nutritionally appreciable. The concentrations of the trace metals; Fe (1.78 mg/kg) and Cu (0.13 mg/kg) were within the Codex and UNBS limits. After three months, acid values of oil samples stored under both conditions showed insignificant differences and compared well with the Codex and UNBS standards. The initial peroxide value (5.3 meq O₂/kg) increased dramatically with samples stored under light exhibiting a significantly greater content (66.7 meq O₂/kg) than those stored in the dark (44.4 meq O₂/kg). The peroxide values under both storage conditions at two weeks met the UNBS (10 meq O₂/kg) and Codex (15 meq O₂/kg) standards, and the average value (13.76 meq O₂/kg) in the dark was acceptable for the Codex standard until week four. On the basis of these results, it is advisable that consumption of crude sunflower oil from small-scale processing plants be limited to within one-month post-processing unless processors adopt practical measures to improve the shelf-life of oil.

Introduction

Lipids are the densest source of energy required in the daily lives of humans [1]. They are composed of triglycerides made of a glycerol backbone with three molecules of fatty acids (FAs): saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs) and polyunsaturated fatty acids (PUFAs) [2]. Vegetable oils like sunflower oil are the primary source of unsaturated fatty acids (UFAs); approximately 20% MUFAs and 69% PUFAs, and fat-soluble vitamins, which play distinctive roles in supporting human health [3]. The evidence of multiple health benefits of UFAs has placed the oil among the most recommended edible oils. Unfortunately, oils with significant amounts of UFAs are prone to oxidation, a chemical process that produces toxic compounds responsible for the general deterioration of oil quality with subsequent effects on nutritional value, safety and sensory properties [4]. According to Chew and Nyam (2020), bioactive compounds preferably natural (e.g., tocopherols, carotenoids, and total phenols) offer antioxidant activity necessary to prevent or delay oil oxidation, thus, preserves product quality and extends its shelf-life. Bioactive compounds with phenolic characteristics act as scavengers through chain-breaking antioxidant mechanism by donating their hydrogen to lipid radicals from the propagation chain of autooxidation [6]. In termination-enhancing antioxidant mechanism, compounds with non-phenolic characteristics self-conjugate with lipid free radicals, yielding radical that rearrange to more stable tertiary free radical and thereby terminate the lipid oxidation chain reaction [7]. However, undesirable minor components such as free fatty acids and trace metals act as prooxidants in the presence of factors that promote oxidation, such as high temperature and light, among others [5].

The increasing demand for edible oils in Uganda has led to the emergence of small-scale sunflower oil processors [8]. Oil extraction method these processors use determines the quantity and quality of the extracted oil [9]. Mechanical oil extraction, both cold and hot, operates at an affordable cost and remains the most common and widely used method [10]. Cold pressing gives low yield, but its high-quality oil is rich in bioactive compounds like tocopherols and phenols which enhance oxidative stability [11]. Small-scale processors hot press sunflower oil for an improved yield, unfortunately, at a continuously high temperature. This process results in the loss of natural antioxidants, hence increasing oxidation and reducing oil quality [9].

Given that these processors have low control of oil extraction parameters, the contents of natural antioxidants and prooxidants in their crude oils cannot be predicted from the values reported for graded oils. From a preliminary assessment, their oil is usually consumed within 1 to 3 months of processing. This study addresses a significant research gap by evaluating the oxidative stability of crude sunflower oil sourced from informal small-scale processors, an underrepresented context in the literature. Unlike refined oils, these unregulated products lack compositional consistency and are commonly consumed within short periods post-processing. No systematic studies have evaluated the deterioration patterns of such oils under typical storage conditions in low-resource settings. Our work provides evidence to guide safe consumption timelines and highlights the implications for food safety in similar informal markets. The purpose of this study was, therefore, to determine the oxidative stability of sunflower oil produced by small-scale processors under light and dark storage conditions for three months to establish its safe consumption shelf-life.

Materials and methods

Collection of oil samples and handling

Nine samples of fresh Crude Sunflower Oil (CSO) were randomly purchased from 9 different small-scale processing plants located in Lira district, sunflower seed processing hub. Each processing plant is managed by a group of processors and we sampled oil from each of the nine plants, representing 100% of the population in that context. Two liters of oil each were purchased directly on 19th October 2019 and divided into two parts in dry 1 L capacity jerrycans, which were previously cleaned with nitric acid and deionized water. One liter of each sample was immediately taken to the Uganda Industrial Research Institute (UIRI) for the determination of natural antioxidants and trace metals. Another 1 L of oil was taken to the Laboratory of Food Chemistry at Gulu University for the determination of oxidation indices.

Determination of natural antioxidants

Vitamin E, general for tocopherols and tocotrienols, is well-known for its antioxidant activity. The two molecules have each four isomers (α-, β-, γ-, δ-) accessible in fatty part of seeds. Sunflower oil predominantly contains α-tocopherol, which accounts for up to 90% of the total tocopherol content [12]. Depending on the analytical method used, other tocopherols and tocotrienols isomers are often undetectable or present only in trace amounts in sunflower oil [13, 14]. Therefore, the analytical method of this research was optimized for α-tocopherol using HPLC [15]. A standard stock solution and three calibration standard solutions were prepared with ethanol (Table 1). α-tocopherol was directly extracted through a mixture of oil samples with methanol at a ratio of 1:3 (v/v). The mixture was vortexed and centrifuged at 3000 rpm for 7 min each. Mobile phase was sonicated methanol at a flow rate of 1.0 mL/min. α-tocopherol was detected at 292 nm with a 7 min retention time.

Table 1. Calibration standard solution preparation and corresponding peak areas of the HPLC chromatograms of α-tocopherol

Std S/No.	Stock standard concentration (mg/ml)	Volume pipetted (ml)	Final diluted volume (ml)	Concentration (mg/ml)	Ret. time (min)	Area response (m3)
1	0.1643	0.6	10	0.0099	7.408	45,155
2	0.1643	5	10	0.0822	7.392	334,516
3	0.1643	0	10	0.1643	7.367	650,759

The content of β-carotene was determined via a liquid HPLC system of filtered and sonicated (A) acetonitrile/water/glacial acetic acid (90/10/2) and (B) methanol/tetrahydrofuran (40/60) [16]. The column temperature was 30 °C and the absorbance was read at 450 nm. For every 5 min, 98% A 2% B and 20% A 80% B were first used then 100% B in the last 20 min during which peak of β-carotene appeared. For the calibration curve, 25 mg of dissolved β-carotene was diluted with PBS to obtain sample solutions.

The total phenol content was assessed spectrophotometrically with Folin-Ciocalteu reagent [17]. Ten grams of gallic acid was mixed with methanol to prepare a standard stock solution and four calibration standard solutions. Two half g of sunflower oil was dissolved in 2.5 mL of n-hexane and subsequently extracted three times by 5-minute centrifugation with 4 mL of methanol and 1 mL of purified water. The extract, 2.5 mL of Folin-Ciocalteu reagent and 5 mL of 7.5% Na₂CO₃ were made to volume. The solutions and samples were stored overnight and then analysed at a wavelength of 765 nm.

Determination of trace metals

The trace metal (Fe, Mn, Cu, and Ni) contents were determined via Atomic Absorption Spectrometry Analyst 400 (PerkinElmer, Waltham, USA) [18]. Approximately 1 g of sunflower oil and 5 mL of concentrated nitric acid were heated at 70–80 °C for 2–3 h. Heating continued at 150 °C overnight with the occasional addition of 3–5 mL of concentrated sulfuric acid and 30% hydrogen peroxide until clear solutions were obtained. The resulting mass was dissolved in 5 mL of deionized water, filtered through Whatman # 42 paper, and brought to 25 mL with 2 N nitric acid. After 25 mL of this mixture was injected into the AAS, the metal contents were calculated from the prepared standard calibration curves.

Determination of oxidation indices

Sample storage

Each liter of CSO separately repacked in clean HDPE 500 mL were tightly sealed with minimal headspace to reduce exposure to oxygen. The oil samples were subjected to two different storage conditions at room temperature (24.5 and 26.7 °C). One set of bottled oils was placed on the laboratory table for storage in light [19], and the second set was wrapped 24 hourlies in aluminium foil (dark) for three months. This method of wrapping is consistent with practices in similar studies, ensuring the integrity of dark storage conditions that approximate common household practices such as storing oils in opaque containers [20]. It shielded samples from both UV and visible light, as these wavelengths are known to catalyse photooxidation in oils, particularly those rich in unsaturated fatty acids. The bottles remained sealed throughout the storage period, except during sampling, which was conducted at two-week intervals using sterile conical centrifuge tubes 50mL, non-wrapped and wrapped with aluminium foil were used to sample oil from each bottle under storage after shaking. The process minimizes oxidative artefacts and ensures that the observed changes in oxidation indices reflect genuine storage effects rather than handling-induced variability.

Determination of acid value and peroxide value

Peroxide value, which captures primary peroxides and AV, which indicates hydrolytic rancidity were measured to address the storage objective of the study because previous studies found them to be sufficient for assessing the early oxidative stability of oils [14, 21].

The American Oil Chemists’ Society method Ca 5a-40 [22] was used to determine the AV. Approximately 28 g of CSO and 50 mL of ethanol were dissolved in a flask. Two mL of phenolphthalein indicator was added, and the mixture was titrated with 0.1 N sodium hydroxide until a pink color appeared and remained for at least 30 s.

The American Oil Chemists’ Society Method Cd 8–53 [23] was used to determine the PV. Five grams of CSO was dissolved in 30 mL of 3:2 acetic acid-chloroform solution. After occasional shaking with 0.5 mL of saturated potassium iodide (KI) solution, 30 mL of distilled water was added, and the mixture was titrated with 0.1 N sodium thiosulfate until the yellow iodine color disappeared. The titration continued with 2 mL of starch indicator until the blue color almost disappeared.

Statistical analysis

Statistical Package for Social Sciences (SPSS) software version 25 and Microsoft Excel Office 2019 were used for data analysis. The results are reported as means ± SDs of independent measurements for each sample. For natural antioxidants and trace metals, the average mean for each parameter was compared with the UNBS and Codex standards via a one-sample t test. To compare the effects of storage conditions, the average means of PV or AV at each two-week interval were compared between light and dark storage conditions via independent sample t tests and between UNBS standards and Codex standards via one-sample t tests, which are represented in the graphics. A linear regression was then performed to define on which day the PV limit quality parameter is reached in the sample for both storage conditions. For all the statistical analyses, the level of significance was 5% (p ≤ 0.05).

Results and discussion

Natural antioxidants

After chromatographic analysis, the peak areas were compared to compute the α-tocopherol content expressed in mg/kg (Table 2). The linearity range of the calibration curve was 0.01–0.164 mg/mL and the correlation coefficient is shown in the calibration plot (Fig. 1). The α-tocopherol content in the CSO ranged from 158.2 to 183.4, with an average of 170.6 mg/kg. The study samples contained two to four times lower amounts of α-tocopherol than the Codex standard recommendation (403–935 mg/kg) for that oil [13]. Similarly, the α-tocopherol of CSO was 511.7 mg/kg [24] and 460 mg/kg [12], among others. These values were greater than the average in our study. However, our work was partly consistent with other studies [25] and [26] reporting that the total tocopherol content in some lines of sunflower seeds ranged from 119 to 491 mg/kg and 178 to 189 mg/kg, respectively. Surprisingly, the α-tocopherol content in this study was greater than total tocopherol content (188 mg/kg) [27]. Sunflower oil is one of the richest sources of α-tocopherol [28], whose form, content and stability are dependent on several factors spread throughout the entire industrial chain, which could explain the marked difference. Previous authors reported that tocopherol content in oil strongly depends on the content of tocopherol accumulated in the seeds, the accumulation period, the cultivation season, the postharvest handling of seeds, and the conditions of oil extraction [29, 30]. In this study, the high temperature applied during the hot-pressing of sunflower seeds could have damaged up to four times the α-tocopherol content compared to cold-pressing. The lower α-tocopherol content implies that sunflower oil produced by small-scale processors may not resist oxidation for a long period.

Table 2. Concentrations of α-tocopherol in different samples of crude sunflower oil

Samples ID	Samples weight (g)	Retention time (mins)	Area response (m3)	Concentration (mg/kg)
CSFO 1	2.526	7.239	255,456	183.426 ± 5.137c
CSFO 2	2.540	7.208	231,147	164.476 ± 7.323ab
CSFO 3	2.558	7.200	250,110	177.193 ± 5.148c
CSFO 4	2.530	7.192	224,260	159.977 ± 4.040a
CSFO 5	2.517	7.180	249,068	179.316 ± 5.462c
CSFO 6	2.560	7.180	225,926	159.460 ± 9.225a
CSFO 7	2.552	7.432	223,581	158.172 ± 9.225a
CSFO 8	2.553	7.195	251,386	178.491 ± 6.593c
CSFO 9	2.536	7.205	245,222	175.082 ± 9.486cb
Average ± SD				170.621 ± 11.034
Codex 210–2001				403–9037

Different letters in the same column indicate significantly different means (P < 0.05)

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Fig. 1

Calibration curve for standard solutions of α-tocopherol

Carotenoids were expressed as β-carotene equivalents (Table 3). The linearity range was 0.005–0.5 mg/mL, and the correlation coefficient is shown in the calibration plot (Fig. 2).

Table 3. Concentrations of β-carotene in different samples of crude sunflower oil

Samples ID	Samples weight (g)	Retention time (mins)	Area response (m3)	Concentration (mg/100 g)
CSFO 1	1.092	11.213	201,808	19.297 ± 1.318c
CSFO 2	1.096	11.213	87,751	7.632 ± 0.491a
CSFO 3	1.038	11.210	113,403	10.824 ± 1.008b
CSFO 4	1.111	11.210	240,386	22.789 ± 0.291d
CSFO 5	1.057	11.213	81,384	7.296 ± 1.444a
CSFO 6	1.020	11.209	85,249	7.923 ± 0.897a
CSFO 7	1.039	11.209	130,052	12.602 ± 1.394b
CSFO 8	1.107	11.207	278,556	26.701 ± 0.852e
CSFO 9	1.101	11.209	136,254	12.474 ± 1.711b
Average ± SD				14.171 ± 6.936

Different letters in the same column indicate significantly different means (P < 0.05)

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Fig. 2

Calibration curve for standard solutions of β-carotene

Beta-carotene was present in all the study samples at various concentrations between 7.3 and 26.7 mg/100 g, with an average content of 14.2 (mg/100 g). Three levels of clustering of processors were apparent, including processors with CSO contents below 10, between 10 and 20 and above 20 mg/100 g. The significant variability in values observed in our study is consistent with the differences reported in carotenoid content within the same plant variety under the same cultivation conditions [31]. Neither internationally nor nationally recognized standards have established an official recommended limit of β-carotene content in CSO. Surprisingly, the average value for β-carotene in this study was up to six times greater than that reported in the literature for CSO [32, 33–34]. Several factors, including genetic and ambient factors, agronomic practices, postharvest management, and processing and storage conditions, could explain the above differences [31]. Through synergistic reactions with other carotenoids and antioxidants, the β-carotene content of CSO in our study is likely to increase the oxidative stability of the oil.

The total phenols content was expressed in terms of milligrams of gallic acid equivalents (GAE) per 100 g and varied from 4.2 to 10.9, with an average of 7.3 mg GAE/100 g (Table 4). Neither internationally nor nationally recognized standards have established an official recommended limit for this an antioxidant in sunflower oil. The average content in this study was relatively similar to the previous value reported for CSO [35] and was within the range (1–12 mg GAE/100 g) recorded by Fine et al. [36]. However, other researchers Kostadinovic-Velickovska and Mitrev [37] and Xuan et al. [38] reported extremely high contents, i.e., 192.8 mg/100 g GAE and 439 mg/100 g GAE, respectively, compared with our results. The differences observed could be associated with environmental characteristics, seed varieties, parts of seeds processed, oil extraction process, and total phenols extraction method [39]. Owing to the antioxidant effect of total phenols, the content recorded in this study may contribute to the oxidation stability of CSO [40].

Table 4. Total phenolic content in different samples of crude sunflower oil

Samples ID	CSFO1	CSFO2	CSFO3	CSFO4	CSFO5
TPC (mg/100 g GAE)	4.840 ± 0.729 ab	5.831 ± 0.317bc	7.995 ± 0.640d	6.727 ± 0.244cd	4.174 ± 0.573a
Samples ID	CSFO6	CSFO7	CSFO8	CSFO9	Average ± SD
TPC (mg/100 g GAE)	7.761 ± 0.408d	10.012 ± 1.191e	7.519 ± 0.293d	10.924 ± 1.080e	7.309 ± 2.214

Different letters in the same column indicate significantly different means (P < 0.05)

Concentrations of trace metals

The CSO samples contained variable amounts of Fe and Cu, except for Mn and Ni, which were undetectable spectrophotometrically (Figs. 3 and 4). The content ranged from 1.2 to 2.6 mg/kg for Fe and 0.1 to 0.2 mg/kg for Cu, with averages of 1.8 and 0.13 mg/kg, respectively. The averages were acceptably below the maximum permissible limits of Fe (5 mg/kg) and Cu (0.4 mg/kg) according to Codex [13] and national [41] standards for crude edible oils (Table 5). These findings are consistent with the results of previous studies conducted in Uganda. Mukasa-Tebandeke et al. [42] and Mukasa-Tebandeke et al. [43] reported Fe contents of 1.75 and 1.70 mg/kg, respectively, and Cu contents of 0.3 and 0.25 mg/kg, respectively, in CSO. This similarity may be attributed to the natural background Fe and Cu contents in the soil and the homogeneity of sunflower cultivation and seeds processing practices across the northern and eastern regions of the country. Farzin and Moassesi [44] reported relatively high contents of Fe (17.66 mg/kg) and Cu (0.25 mg/kg), whereas Bashir et al. [45] reported relatively low contents (0.6–1.1 mg/kg). The difference might be attributed to differences in the geographical environment, oil processing process, storage methods and metal determination techniques used [46]. The results of the present study indicate that the Fe and Cu contents in CSO are acceptable and pose fewer risks to oxidation and human health.

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Fig. 3

Concentration of iron in small-scale pressed sunflower oil compared to Codex and Uganda standards

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Fig. 4

Concentration of copper in crude sunflower oil compared to Codex and Uganda standards

Table 5. Comparison of trace elements concentrations with standards

References	Trace elements concentrations (mg/kg)
	Fe	Cu	Mn	Ni
This study	1.784 ± 0.492a	0.126 ± 0.050a	ND¹	ND
Uganda Standard 299:2013	5b	0.4b	NA²	NA
Codex Standard 210–2001	5b	0.4b	NA	NA

¹ND: not detected; ²NA: not available; different letters in the same column indicate significantly different means

Oxidative indices

Acid value and PV are common indicators of oxidative stability in oils [14, 21].

Acid value quantifies free fatty acids resulting from triglyceride hydrolysis, often expressed as mg KOH/g oil. Alternatively, AV is defined as the amount in milligrams of potassium hydroxide needed to neutralize FFA present in 1 g of oil sample. FFA was expressed as a percentage of oleic acid and converted into AV by multiplying factor of 1.99. Figure 5 shows the variations in the AV of CSO stored at room temperature in light and dark conditions over three months. The initial average AV (2.4 mg KOH/g) slowly increased to 3 mg KOH/g in light, and a similar trend was observed in the dark over the storage period. This slow increase in AV across the two storage conditions may result from the hydrolysis of triglycerides due to residual enzymatic activity and/or limited moisture presence. This is consistent with findings of Crapiste et al. (1999) that reported a slow hydrolytic degradation in sealed oil during ambient storage, particularly due to residual enzymatic activity and/or limited moisture presence. Statistically, no significant difference (p >0.05) was observed between the two storage conditions, and the values were within the acceptable limits of 4 mg KOH/g according to the standards for cold-pressed and virgin oils [13, 41]. It is obvious that irrespective of the storage period and conditions, the AV of CSO stored at 30 °C for 98 days remained nearly constant [47]. In contrast, Kucuk and Caner (2005) reported a significant increase in AV for refined sunflower oil exposed to light over those kept in the dark after 3, 6 and 9 months of storage. The difference is highly dependent of the experimental conditions, but, AV, while a useful parameter, does not necessarily correlate with oxidation unless combined with exposure to oxygen or light [49]. Besides, it may not be sensitive to changes in oxidative status in the absence of moisture or microbial lipase activity.

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Fig. 5

Evolution of average acid value in crude sunflower oil stored in light and dark for three months compared with standards

PV measures the concentration of hydroperoxides formed in the early stages of lipid oxidation and is reported in meq O₂/kg. Peroxide value measures the status of oxidation at the early stage where hydroperoxides are the predominant products. It is expressed as milliequivalents of active oxygen per kilogram of oil. On average, the initial PV increased from 5.3 to 66.7 meq O₂/kg for samples stored in light and 44.4 meq O₂/kg for those stored in the dark over three months (Figs. 6 and 7). Peroxide values from both storage conditions were used to perform a linear regression to define on which day the PV limit quality parameter is reached in the samples as per Uganda (10 meqO2/Kg) and Codex (15 meqO2/Kg) standards. On average in dark, PV reached the end point for rancidity per Uganda standard at 16.9 days and Codex standard at 27.3 days (Table 6; Fig. 6). On average in light, PV reached the end point for rancidity per Uganda standard at 13.1 days and Codex standard at 19.7 days (Table 7; Fig. 7). A significant difference (p < 0.05) between the two storage conditions was observed from week four (Fig. 8). Importantly, the rapid increase in the PV irrespective of the storage conditions could be related to the high linoleic acid in the oil and the lower α-tocopherol contents, hence increasing the susceptibility to oxidation [43]. The greater increase in the PV in light could be attributed to the penetration of light photons in oil samples exposed to light, which trigger photo-oxidation [50], where light photons catalyse the reaction of singlet oxygen with UFAs that generate free radicals. Other than that, the permeability of oil packaging material to oxygen and presence/absence of headspace also interfere and cause variations in PV [48]. The general composition of oils and factors promoting oxidation can adversely accelerate oxidation, thus reducing the shelf-life of the product. There is a high chance that the CSO under study could contribute to adverse health outcomes.

Table 6. Regression coefficients and determination coefficients (R²) for peroxide values (PV) from crude sunflower oil during storage in dark

Parameters	Values
Slope (a)	0.4811
Intercept (b)	1.8635
R3	0.9786
Estimated time for Uganda standard, 10 meq O₂/kg	16.9 days
Estimated time for Codex standard, 15 meq O₂/kg	27.3 days

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Fig. 6

Linear regression of peroxide values from crude sunflower oil stored in dark compared to Uganda standard

Table 7. Regression coefficients and determination coefficients (R²) for peroxide values (PV) from crude sunflower oil during storage in light

Parameters	Values
Slope (a)	0.7555
Intercept (b)	0.0851
R3	0.981
Estimated time for Uganda standard, 10 meq O₂/kg	13.1 days
Estimated time for Codex standard, 15 meq O₂/kg	19.7 days

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Fig. 7

Linear regression of peroxide values from crude sunflower oil stored in light compared to Codex standard

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Fig. 8

Comparison of peroxide values in crude sunflower oil under dark and light storage conditions

Conclusion

The study demonstrated that crude sunflower oil from small-scale processing plants contains appreciable levels of natural antioxidants, including β-carotene and total phenols. However, the concentration of α-tocopherol, the principal form of vitamin E in sunflower oil, was significantly lower than Codex recommended levels. The concentrations of trace metals were within safe limits as established by both Codex and UNBS standards for crude edible oils. Acid values remained within acceptable thresholds throughout the three-month storage period, indicating limited hydrolytic degradation. In contrast, peroxide values increased markedly under both storage conditions, particularly when oil samples were exposed to light. While peroxide levels met Codex and UNBS standards within the first two weeks, oil samples stored in dark exceeded the Codex limit after approximately one month. These findings suggest that crude sunflower oil from small-scale processors may undergo quality deterioration beyond one month of storage, especially under suboptimal conditions. To reduce potential risks associated with oxidation, it is advisable that consumption of such oil be limited to within one-month post-processing unless enhanced preservation methods are employed. Small-scale processors are encouraged to adopt cold-pressing techniques to retain natural antioxidants or consider refining and fortifying edible oils with approved antioxidants to improve shelf-life and product stability.

Practical application

These findings offer practical insights not only for local consumers and processors but also for food safety policymakers working to improve nutritional standards in informal food systems. The results are applicable across many low- and middle-income countries where small-scale oil production is widespread, and regulation is limited. This study supports broader global efforts to promote sustainable and safe food systems under resource-constrained conditions.

Limitations and recommendations

This study focused on oxidative stability and minor components of crude sunflower oil sourced from small-scale processing plants. However, detailed information on seed characteristics and processing parameters that influence oxidation, such as seed variety, pressing temperature, and postharvest handling was not available, as these are typically undocumented in informal production settings. While capacity-building efforts should support small-scale processors in documenting these critical factors, future research should also account for seed variety, growing season and environmental conditions, postharvest management, and pressing conditions to improve traceability and facilitate quality control. Second, the study focused exclusively on α-tocopherol, given its predominance in sunflower oil. Future studies to investigate the full profile of vitamin E isomers and deepen understanding of their individual antioxidant roles in oils produced by small-scale processors, particularly during storage. Finally, this study measured only primary oxidation indices. Future research should include both primary and secondary oxidation markers, as well as screen for potential food safety hazards, to provide a more comprehensive assessment of oil stability and safety in small-scale processing systems.

Acknowledgements

We are grateful to Gulu University and the MasterCard Foundation (MCF) through the Regional UniversityForum for Capacity Building in Agriculture (RUFORUM).

Author contributions

Mededode Monique Sognigbe: Conceptualization, methodology, data collection and analysis, writing the original draft.Solomon Olum: Supervision, review & editing.Duncan Ongeng: Supervision, review & editing.

Funding

This research was supported by RUFORUM.

Data availability

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

Approval to carry out this research was obtained from Gulu University Research Ethics Committee (GUREC) under application No. GUREC-022-20. Sampling of small-scale pressed sunflower oil in Lira adhered to corresponding regulations not to reveal the identities of the processing plants.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.

Publisher’s note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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