Peanut oil is one of the most widely used cooking oils globally, valued for its rich nutritional profile and versatility. With global peanut production reaching 50.11 million tons in 2022/2023, peanuts contribute significantly to the world’s oil crop production, accounting for 8% of the total.
The oil extracted from peanuts is not only high in fat content (45%-60%) but also packed with essential nutrients such as vitamin E, phytosterols, and zinc.
However, despite its benefits, the safety and quality of peanut oil can be compromised by harmful substances like aflatoxin B₁ (AFB₁), benzo[a]pyrene (BaP), 3-chloro-1,2-propanediol esters (3-MCPDE), and trans-fatty acids (TFAs).
Introduction: The Importance of Safe Peanut Oil Production
Peanut oil is a dietary staple in many cultures, thanks to its balanced composition of monounsaturated fats (41%), saturated fats (19%), and polyunsaturated fats (38%). These fats, particularly oleic and linoleic acids, support heart health and overall well-being.
However, the journey from peanut cultivation to bottled oil is fraught with risks. Environmental factors, improper storage, and high-temperature processing can introduce harmful substances into the oil.
For example, peanuts are highly susceptible to fungal infections, especially from Aspergillus flavus, which produces the deadly carcinogen aflatoxin B₁. Similarly, refining processes like deodorization and frying can generate toxic compounds such as BaP and TFAs.
Understanding Aflatoxin B₁ (AFB₁) and Its Impact on Peanut Oil
Aflatoxin B₁, produced by molds like *Aspergillus flavus*, is one of the most dangerous contaminants in peanut oil. Classified as a Group I carcinogen by the World Health Organization (WHO), AFB₁ is 10 times more toxic than potassium cyanide.
It thrives in warm, humid conditions, making peanuts vulnerable during growth and storage. Once present in oil, AFB₁’s lipophilic nature allows it to dissolve easily, resisting traditional removal methods.
The WHO estimates that 25% of global crops are contaminated with aflatoxins, with 2% deemed unsafe for consumption.
This contamination not only threatens human health but also causes economic losses, especially in developing nations reliant on peanut farming.
To combat AFB₁, researchers have developed advanced detection methods. High-Performance Liquid Chromatography (HPLC) is widely regarded as the gold standard due to its precision, detecting AFB₁ at concentrations as low as 1 nanogram per liter.
Enzyme-Linked Immunosorbent Assay (ELISA) is another popular method, offering rapid results for large-scale screening.
Emerging technologies like Laser-Induced Fluorescence-High-Performance Capillary Electrophoresis (LIF-HPCE) further enhance detection sensitivity, ensuring even trace amounts of AFB₁ are identified.
Physical methods like UV irradiation can degrade up to 99% of the toxin, though excessive use may harm the oil’s nutritional value. Chemical treatments, such as ozone exposure, break down AFB₁’s toxic structure without altering the oil’s color or acidity.
Biological approaches, including the use of enzymes like laccase from *Bacillus licheniformis*, offer eco-friendly solutions by converting AFB₁ into harmless compounds. These methods, when combined, provide a robust defense against aflatoxin contamination.
Benzo[a]pyrene (BaP): A Hidden Threat in Processed Peanut Oil
Another critical contaminant in peanut oil is benzo[a]pyrene (BaP), a polycyclic aromatic hydrocarbon (PAH) formed during high-temperature processes like roasting and frying. BaP is a known carcinogen, linked to lung, liver, and skin cancers.
When ingested, BaP is metabolized into benzo[a]pyrene diol epoxide (BPDE), which binds to DNA and causes mutations. Its stability and lipophilic nature make it difficult to eliminate once it enters the oil. Detecting BaP requires sophisticated techniques.
High-Performance Liquid Chromatography (HPLC) paired with fluorescence detectors remains the most reliable method, achieving detection limits of 0.1 micrograms per kilogram. Solid Phase Extraction (SPE) is often used to purify oil samples before analysis, improving accuracy.
Recent innovations, such as gold nanoparticle-based immunoassays, promise faster and portable detection, though they are still under development.
To remove BaP, adsorption techniques are highly effective. Activated carbon, with its porous structure, traps BaP molecules, achieving removal rates above 90%.
Molecularly Imprinted Polymers (MIPs), designed to specifically bind BaP, offer even greater precision. Additionally, research into biodegradation using enzymes like cytochrome P450 1A1 (CYP1A1) shows potential, though practical applications in oil processing are still evolving.
3-Chloro-1,2-Propanediol Esters (3-MCPDE): Challenges in Oil Refining
3-MCPDE, a chlorinated compound formed during oil refining, poses significant health risks. When ingested, it breaks down into 3-MCPD, a possible human carcinogen associated with kidney damage and infertility.
The European Union has set strict limits for 3-MCPDE in vegetable oils (1.25 micrograms per kilogram), pushing the industry to adopt safer practices.
Detecting 3-MCPDE involves advanced chromatography. Ultra-Performance Convergent Chromatography (UPC²) uses supercritical carbon dioxide to separate 3-MCPDE from other components, ensuring high accuracy.
Gas Chromatography-Mass Spectrometry (GC-MS) with isotope labeling is another reliable method, minimizing errors during analysis. Reducing 3-MCPDE levels requires refining process adjustments.
For example, dividing deodorization into two stages—low-temperature distillation followed by high-temperature steam stripping—can cut 3-MCPDE by 40-60%.
Enzymatic treatments, such as using *Candida rugosa* lipase to break down 3-MCPDE, also show promise, though scalability remains a challenge.
Trans-Fatty Acids (TFAs): Risks and Mitigation in Peanut Oil
Trans-fatty acids (TFAs), formed during hydrogenation and high-heat processing, are notorious for raising LDL cholesterol and increasing heart disease risk. The WHO recommends limiting TFA intake to less than 1% of total energy consumption, prompting stricter regulations worldwide.
Detecting TFAs relies on techniques like Gas Chromatography (GC), which separates fatty acid isomers with high precision. Infrared Spectroscopy (IR) offers a quicker alternative, identifying trans double bonds at specific wavelengths, though it struggles with low concentrations.
To reduce TFA formation, manufacturers are adopting low-temperature deodorization (below 200°C) and electrochemical hydrogenation, which minimizes trans-fat production.
Antioxidants like resveratrol and ascorbic acid also play a role by neutralizing free radicals generated during heating, further protecting oil quality.
The Generation and Harm of 3-MCPDE in Peanut Oil
3-MCPDE are chlorinated process contaminants formed during edible oil refining, particularly during deodorization (180–270°C). They originate from the reaction of chloride ions (e.g., from bleaching earth) with glycerol esters.
Upon ingestion, 3-MCPDE hydrolyzes into 3-MCPD, a Group 2B carcinogen (possibly carcinogenic to humans) linked to kidney damage and infertility. The European Union mandates a maximum limit of 1.25 μg/kg for 3-MCPDE in vegetable oils.
Ultra-Performance Convergent Chromatography (UPC²): Uses supercritical CO₂ as a mobile phase to separate 3-MCPDE with high resolution.Gas Chromatography-Mass Spectrometry (GC-MS): The 13C isotope dilution method quantifies 3-MCPD with <10% margin of error, making it the regulatory standard.
Conclusion:
Ensuring the safety and quality of peanut oil demands a multi-faceted approach. From advanced detection technologies like HPLC and GC-MS to innovative removal methods such as ozone treatment and enzymatic degradation, the industry is making strides in combating harmful contaminants.
Equally important are preventive measures, such as storing peanuts in low-humidity environments and using nitrogen flushing to preserve oil freshness.Ongoing research into nanomaterials and genetically modified enzymes offers exciting possibilities for the future.
For instance, graphene oxide-based adsorbents could revolutionize toxin removal, while tailored enzymes might break down contaminants more efficiently. Collaboration between scientists, policymakers, and manufacturers will be key to implementing these advancements globally.
Power Terms
Aflatoxin B1 (AFB1): A toxic compound produced by molds like Aspergillus flavus and Aspergillus parasiticus. It is highly carcinogenic and commonly found in crops like peanuts stored in warm, humid conditions. AFB1 is critical in food safety because even small amounts can cause liver cancer. Detection methods include chromatography and immunoassays. For example, moldy peanuts contaminated with AFB1 must be removed to prevent toxic oil production.
Benzo[a]pyrene (BaP): A polycyclic aromatic hydrocarbon (PAH) formed during high-temperature cooking or incomplete combustion. BaP is dangerous because it damages DNA, increasing cancer risk. It enters the body through food, air, or skin contact. Grilled meats or smoked foods often contain BaP. Regulatory limits ensure its levels in edible oils, like peanut oil, remain low.
3-Chloro-1,2-Propanediol Esters (3-MCPDE): Harmful compounds formed during oil refining, especially at high temperatures. These esters break down into 3-MCPD, which may harm kidneys and fertility. Found in refined vegetable oils, their levels depend on processing methods. For example, deodorization steps in peanut oil production can generate 3-MCPDE. Reducing refining temperatures helps minimize their formation.
Trans-Fatty Acids (TFAs): Unsaturated fats with a trans chemical structure, often created during hydrogenation or high-heat processing. TFAs raise bad cholesterol (LDL) and lower good cholesterol (HDL), increasing heart disease risk. Fried foods and baked goods are common sources. In peanut oil, TFAs form during deodorization. Health guidelines recommend limiting TFA intake to less than 1% of daily calories.
Polycyclic Aromatic Hydrocarbons (PAHs): A group of chemicals produced by burning organic materials. PAHs like BaP are carcinogenic and enter food through smoke or polluted environments. Peanut oil can absorb PAHs if exposed to smoke during roasting. Regulatory agencies monitor PAH levels to ensure food safety.
Chloropropanol Esters: Contaminants formed when chloride reacts with fats during oil refining. 3-MCPDE is the most studied type. These esters are linked to organ damage and are common in processed oils. Reducing chloride content in raw materials lowers their formation.
Thin-Layer Chromatography (TLC): A lab method to separate and identify compounds like AFB1. A sample is placed on a plate, and solvents move components at different speeds. TLC is cost-effective but less precise than modern techniques. It’s used in initial screenings for toxins.
High-Performance Liquid Chromatography (HPLC): A precise technique to detect contaminants like AFB1 or BaP. It pumps a liquid sample through a column, separating components based on chemical properties. HPLC is widely used in labs for its accuracy, often achieving detection limits as low as nanograms per liter.
Enzyme-Linked Immunosorbent Assay (ELISA): A test using antibodies to detect toxins like AFB1. It’s fast and suitable for large-scale screening. For example, ELISA kits can quickly identify contaminated peanut batches. However, cross-reactivity with similar compounds may affect accuracy.
Gas Chromatography-Mass Spectrometry (GC-MS): Combines gas chromatography and mass spectrometry to identify chemicals like TFAs. It separates compounds (GC) and analyzes their molecular structure (MS). GC-MS is highly accurate but requires expensive equipment and skilled operators.
Adsorption: A process where materials like activated carbon trap toxins. For example, modified clays can adsorb BaP from peanut oil. Adsorption preserves oil quality but may require multiple treatments for full toxin removal.
Biodegradation: Using microbes or enzymes to break down toxins. Certain bacteria and fungi degrade AFB1 into harmless substances. This eco-friendly method is promising but needs more research for large-scale oil detoxification.
Physical Refining: Oil processing steps like filtration or steam distillation to remove impurities. Unlike chemical refining, it avoids harsh solvents. Physical refining minimizes 3-MCPDE formation but may retain more natural nutrients.
Chemical Treatments: Using acids, bases, or oxidants to neutralize toxins. Ozone degrades AFB1 by breaking its toxic structure. However, chemicals like sodium hydroxide may alter oil flavor or nutritional value.
Deodorization: A high-temperature step in oil refining to remove odors. While necessary, it can form TFAs and 3-MCPDE. Optimizing temperature and time reduces harmful byproducts.
Hydrogenation: Adding hydrogen to oils to solidify them, creating TFAs. Partially hydrogenated oils are banned in many countries due to health risks. Alternatives like interesterification produce zero-TFA oils.
Oxidation: A reaction where oxygen degrades fats, causing rancidity. Oxidized oils lose nutritional value and develop harmful compounds. Antioxidants like vitamin E slow oxidation in peanut oil.
Nutritional Value: The health benefits of peanut oil, including monounsaturated fats and vitamin E. Preserving nutrients while removing contaminants is key to producing high-quality oil.
Food Safety: Practices to ensure edible oils are free from toxins. Monitoring AFB1, BaP, and 3-MCPDE levels protects consumers. Regulations and testing protocols are critical for industry compliance.
Carcinogen: A substance that causes cancer. AFB1 and BaP are classified as Group 1 carcinogens by the WHO. Avoiding exposure through proper storage and processing is vital.
Mycotoxins: Toxic compounds from molds. AFB1 is a mycotoxin threatening global food supplies. Preventing mold growth in peanuts reduces contamination risks.
Antioxidants: Compounds that prevent oxidation. Natural antioxidants like vitamin E in peanut oil extend shelf life and protect against harmful free radicals.
Pathogens: Microbes causing contamination. Aspergillus molds producing AFB1 are pathogens controlled through drying and proper storage.
Quality Control: Procedures to maintain oil safety and consistency. Testing raw materials, refining processes, and final products ensures standards are met.
Lipophilicity: A substance’s ability to dissolve in fats. AFB1’s lipophilicity lets it accumulate in peanut oil, making removal challenging. Adsorption or chemical methods target these fat-soluble toxins.
Reference:
Ni, Z., Ouyang, X., Nie, A., Huang, L., Li, R., Li, J., & Chen, P. (2025). The control technology of harmful substances impacting the quality of peanut oil: A review. Grain & Oil Science and Technology.
