Olive Oil Analysis with Gas Chromatography and Time-of-Flight Mass Spectrometry

In the food industry, food product analysis is crucial for QC purposes, authenticity of products and materials, and brand awareness. The combination of GC and high-resolution TOFMS provides reliable analyte determinations with unprecedented mass accuracy through isolation of individual analytes within complicated matrices at both mass spectral and chromatographic resolution.

This article discusses the application of these analytical tools for a non-targeted volatile analysis of aroma and flavor analytes present in a commercially available light and extra-virgin olive oils samples obtained from a single manufacturer, with data analysis using LECO'S ChromaTOF-HRT software.

Experimental Procedure

This experiment analyzed light and extra-virgin olive oils obtained from the same manufacturer by pipetting 2g of each sample into 10mL SPME vials and subsequent sealing with septum caps. A divinylbenzene/carboxen/polydimethylsiloxane fiber was used to perform HS-SPME sampling. The experiment involved incubation of each sample at 40°C for five minutes before performing the extraction for 25 minutes at the same temperature. GC-TOFMS (Pegasus GC-HRT) conditions are summarized in the following table:

GC-TOFMS (Pegasus® GC-HRT) Conditions
Injection SPME desorption for 2 min @ 250°C
Carrier Gas He @ 1.5 ml/min
Column Rxi-5ms, 30 m x 0.25 mm i.d. x 0.25 µm coating (Restek, Bellefonte, PA, USA)
Temperature Program 2 min at 40°C, ramped 12°C/min to 250°C, held 3 min
Transfer Line Temperature set to 250°C
Acquisition Mode High Resolution, R = 25,000 (FWHM)
Mass Range 33-400 m/z
Acquisition Rate 6 spectra/s
Source Temp 250°C

LECO'S ChromaTOF-HRT software was used for data analysis. The “Reference” feature within the ChromaTOF-HRT software was used as a selection tool to identify the differences of analytes present in the light and extra-virgin olive oils. The analyte’s relative concentration in the sample relative to a user-specified reference was calculated by this analysis tool.

Each analyte peak was then subsequently classified to reveal the correlation with the reference. Analytes found in both the sample and reference were designated as "Match" or "Out of Tolerance" based on their relative concentrations against a user-specified threshold. Analytes that were found only in the sample or reference are tagged “Unknown” and “Not Found,” respectively.

Experimental Results

LECO's Pegasus GC-HRT was used to characterize and discern between light and extra-virgin olive oil samples obtained from a single manufacturer. ChromaTOF's automated processing tools were employed to identify the analytes present in these samples. The detected compounds were terpenes, ketones, aldehydes, alcohols, esters, and much more. These aroma and flavor analytes may be helpful to gain insights into the sensory properties of the samples.

Figure 1 presents the overlaid TIC chromatograms for each sample, apparently showing many differences. These differences were then further characterized automatically using the “Reference” feature of the ChromaTOF-HRT software to determine sample-differntiating analytes, which may be helpful to detect food fraud.

Representative TIC chromatograms are overlaid for extra-virgin olive oil (orange trace) and light olive oil (green trace) from the same manufacturer.

Figure 1. Representative TIC chromatograms are overlaid for extra-virgin olive oil (orange trace) and light olive oil (green trace) from the same manufacturer.

In this experiment, the light olive oil was used as the sample and the extra-virgin olive oil was used as the reference. Peaks in the sample tagged "Out of Tolerance" or "Not Found" represent the extra-virgin olive oil, whereas "Out of Tolerance" and "Unknown" represent the light olive oil. a-cubebene shown in Figure 1 is an example for a "Not Found" analyte. It is a sesquiterpene exhibiting herbal odor properties.

The XIC chromatogram reveals that the analyte was present in the extra-virgin olive oil, but absent in the light olive oil. Figures 2 and 3 present two "Out of Tolerance" examples having low (phenylethyl alcohol) and high (heptanes) concentrations, respectively, with respect to the reference. Phenylethyl alcohol with floral odor properties represented extra-virgin olive oil, whereas heptanes with sweet and ethereal odor properties represented the light olive oil. In both cases, the analytes were identified by comparison with NIST library databases, with mass accuracies down to 1ppm for the molecular and fragment ions.

Phenylethyl alcohol, an "Out of Tolerance" analyte indicative of extra-virgin olive oil, is shown.

Figure 2. Phenylethyl alcohol, an "Out of Tolerance" analyte indicative of extra-virgin olive oil, is shown.

Heptane, an "Out of Tolerance" analyte indicative of light olive oil, is shown.

Figure 3. Heptane, an "Out of Tolerance" analyte indicative of light olive oil, is shown.

Conclusion

The study results show the advantage of using LECO's analytical tools in the characterization of complex food samples and identification of food fraud. With an unprecedented resolution and mass accuracy, the Pegasus GC-HRT differentiates and reliably determines the individual analytes present in the complex sample matrices, using its automated data processing tools. The mass accuracy of below 1ppm is in good agreement with the library search results.

The "Reference" feature in LECO's ChromaTOF-HRT software was used for the demonstration of a differential analysis approach to compare between light and extra-virgin olive oil samples, determining analyte similarities and dissimilarities between the samples. This data analysis approach provides feature selection capabilities to identify characteristic analytes present in each sample type. Determination of these characteristic analytes facilitates determining food fraud.

This information has been sourced, reviewed and adapted from materials provided by LECO Corporation.

For more information on this source, please visit LECO Corporation.

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