Characterization of Adulterated Olive Oils in Cases of Food Fraud by Comprehensive Two-Dimensional Gas Chromatography with Time-of-Flight Mass Spectrometry (GC×GC-TOFMS)

Significance of the topic

Adulteration of olive oil is among the most prevalent food frauds, driven by economic incentives. Reliable detection methods are critical for protecting consumers, preserving product integrity and ensuring compliance with quality standards. Comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC×GC-TOFMS) offers enhanced separation and sensitivity for complex oil matrices, making it a powerful tool in authenticity testing.

Objectives and study overview

This study aimed to evaluate GC×GC-TOFMS for the characterization of extra virgin olive oil (EVOO) and common adulterant oils. Key goals included:

• Developing chromatographic fingerprints for pure EVOO and other edible oils (peanut, vegetable, grape seed).
• Simulating adulteration at 50% and 10% levels.
• Identifying marker compounds that differentiate oil varieties and detect blending.

Methods and instrumentation

Sample preparation involved diluting each oil 1:10 in cyclohexane. Adulteration mixtures of EVOO with peanut, vegetable or grape seed oil were prepared at 50% and 10% ratios. GC×GC-TOFMS analyses were performed on a Pegasus® 4D system with:

• Agilent 7890 GC with GERSTEL MPS2 Autosampler
• Dual-stage quad jet thermal modulator and secondary oven (+10 °C offset)
• Rxi-5Sil MS primary column (30 m×0.25 mm×0.25 µm)
• Rxi-17Sil MS secondary column (1.25 m×0.18 mm×0.18 µm)
• Transfer line and source at 250 °C, modulator period 3 s (+15 °C offset)
• Carrier gas: helium at 1.0 mL/min, splitless injection (1 µL at 250 °C)
• TOFMS acquisition at 200 spectra/s over m/z 35–500
• Data processed with ChromaTOF® 4.50 software

Main results and discussion

GC×GC chromatography produced detailed two-dimensional fingerprints, revealing both common and unique volatile profiles. Feature selection using Fisher Ratio highlighted analytes with the greatest between-class variance relative to within-class variance. Key findings included:

• Identification of approximately 15 marker compounds in EVOO, including norbornane, octane, nonanal and α-farnesene.
• Peak area differences for these analytes across pure oils and adulteration mixtures, demonstrating sensitivity to as little as 10% blending.
• PCA without feature selection showed overlapping clusters, while PCA with selected markers achieved clear separation of each oil type and adulteration level.

Benefits and practical applications

GC×GC-TOFMS coupled with statistical feature selection provides:

• High confidence in detecting low-level adulteration through targeted markers.
• Robust chemometric models for rapid screening and quality control in production and regulatory labs.
• Comprehensive profiling that supports both targeted and non-targeted fraud detection.

Future trends and opportunities

Advancements to further improve olive oil authentication may include:

• Optimized sampling and extraction protocols for minor component enrichment.
• Expansion of marker libraries covering diverse geographic and varietal origins.
• Integration of machine learning algorithms for automated pattern recognition.
• Application to solid-phase extraction and consumer-grade screening devices.

Conclusion

This work demonstrates that GC×GC-TOFMS, combined with Fisher Ratio feature selection and PCA, can effectively characterize edible oils and detect adulteration at low blending levels. The approach yields distinct chromatographic fingerprints and marker panels suitable for routine authenticity testing, supporting food safety and industry quality assurance.