The research team at Nestlé Research in Lausanne, Switzerland, develops innovative solutions for food quality and authenticity. Their work, particularly in detecting adulteration in edible oils, plays a key role in ensuring the authenticity of the global food supply chain. By employing advanced chromatographic techniques, the team enhances analytical methods, making a significant contribution to food quality and authenticity. Tiên Do from CAMAG collaborated on this project, contributing to the development of the methods.
Introduction
The evaluation of edible oil authenticity has become increasingly important due to rising incidents of oil adulteration, where low-quality or non-edible oils are mixed with premium oils for economic gain. Such fraudulent practices not only erode consumer trust but also pose health risks. As adulteration methods become more sophisticated, reliable and efficient detection methods are needed.
This study evaluates the use of HPTLC as a cost-effective and efficient tool for monitoring oil authenticity. Both untargeted (fingerprint profiling) and targeted (mineral oil detection) methods were applied to palm, sunflower, and rapeseed oils, demonstrating the capability to detect adulteration at levels between 5% and 25%.
HPTLC offers numerous advantages, including the ability to analyze multiple samples simultaneously with lower solvent consumption. It is also adaptable to different detection protocols and highly reproducible across laboratories. As a result, HPTLC is positioned as an ideal method for industrial applications requiring rapid and user-friendly solutions for oil quality monitoring.
Sample preparation
Edible oils, including sunflower, rapeseed, and palm oil, were collected from various suppliers and prepared for analysis. Authentic oil batches were diluted using cyclopentyl methyl ether (CPME) as the solvent (25.0 μL of oil in 3.0 mL of CPME). The samples were vortexed for 5 seconds, and 1.0 mL of the resulting solution was transferred to a vial for single-use analysis.
Chromatogram layer
HPTLC silica gel 60 F254 plates (Merck) were used for vegetable oil analysis, while RP18 F254 plates (Merck) were employed for mineral oil adulteration detection. For mineral oil method, the plates were prewashed with methanol and heated at 110 °C for 15 minutes before application.
Sample application
Oil samples were applied as 6.0 mm bands onto the plates using an Automatic TLC Sampler 4.
Chromatography
Plates were developed in the ADC 2 to a migration distance of 70 mm for edible oils and 30 mm for mineral oil detection. A mixture of acetonitrile and CPME (7:3 V/V) was used as the developing solvent for vegetable oils, and cyclohexane was used for mineral oil detection. Relative humidity was adjusted to 33% for 10 minutes only for the edible oil method, and chamber saturation was maintained for 20 minutes for both methods.
Post-chromatographic derivatization
After development, chemical derivatization was performed using anisaldehyde reagent for edible oils and primuline reagent for mineral oils. The plates were sprayed with the respective derivatization reagent using the Derivatizer. In the case of anisaldehyde reagent the plates were heated at 100 °C for 3 minutes, and after primuline at 40 °C for 3 min.
Documentation
The plates were documented using the TLC Visualizer 2 at UV 366 nm for mineral oils after derivatization with primuline, and in white light (transmission) for edible oils after derivatization with anisaldehyde reagent. Peak profiles from images (PPIs) were analyzed with the visionCATS software, and peak heights were recorded to assess the presence of adulterants.
Data analysis
Statistical analysis was conducted to assess batch variability and adulteration detection. The peak heights from RF values ranging between 0.2 and 0.8 were used to evaluate oil authenticity. The detection limit for adulteration was established at 5% for both edible oils and mineral oils.
Results and discussion
The results demonstrate the successful application of HPTLC in detecting adulteration in edible oils. The method provided clear and reproducible chromatographic fingerprints for sunflower, rapeseed, and palm oils. Each oil type exhibited unique RF values, enabling the differentiation of authentic oils from adulterated ones.
Fingerprints of tested oils with corresponding RF (represented with a red line), HPTLC plate in white light (transmission) after derivatization with anisaldehyde reagent; sunflower oil (A), rapeseed oil (B), and palm oil (C); (https://creativecommons.org/licenses/by/4.0/legalcode)
The following HPTLC chromatograms reveal the detection of adulteration in sunflower oil. Samples adulterated with cotton, safflower, corn, sesame, and soy oils were analyzed, and the corresponding RF values for each adulterant are marked with dashed lines. Adulteration was detected at RF values specific to each adulterant, such as RF 0.38 for cotton oil and RF 0.49 for sesame oil. The clear distinction between authentic and adulterated sunflower oil samples demonstrates the sensitivity of the HPTLC method, which successfully detected adulteration at levels as low as 5%.
HPTLC chromatograms in white light (transmission) after derivatization with anisaldehyde reagent: Sunflower oil adulterated with cotton oil (A), safflower oil (B), corn oil (C), sesame oil (D), and soy oil (E) with the corresponding adulteration RF’s (represented with a dash lines); (https://creativecommons.org/licenses/by/4.0/legalcode)
Adulteration was detected at RF values around 0.8 for mineral oil and paraffin wax, clearly distinguishing them from the authentic palm oil sample. The high sensitivity of the HPTLC method allowed for the detection of adulteration at levels below 5%, demonstrating its effectiveness in identifying hazardous non-edible oil contaminants such as mineral oils.
HPTLC chromatograms in UV 366 nm after derivatization with primuline reagent: Palm oil adulterated with mineral oil (A) and paraffin wax (B); (https://creativecommons.org/licenses/by/4.0/legalcode)
Conclusion
HPTLC proved to be a valuable tool for detecting adulteration in edible oils, offering a high-throughput, reliable, and relatively simple method. The method is well-suited for industrial applications, ensuring food quality and authenticity in the global edible oil market.
Literature
[1] Paul Rogeboz et al. Food Analytical Methods (2024) 17:1336–1347
Further information is available on request from the authors.
Contact
Paul Rogeboz, Société des Produits Nestlé SA, Nestlé Research, 1000, Lausanne, Vers-Chez-Les-Blanc, Switzerland, paul.rogeboz@rd.nestle.com