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Note 98: Flavor and Aroma Profiles of Truffle Oils by Thermal Desorption GC/MS

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Ronald E. Shomo, II, Robert Frey, John J. Manura, and Christopher Baker
Scientific Instrument Services
1027 Old York Road, Ringoes, NJ 08551
(presented at ASMS 2014)

Introduction

The fraudulent food business costs consumers in excess of $100 billion dollars per year.1 Not only are consumers paying big bucks for falsely advertised foods, but what is in the bogus foods could be deadly to consumers. An example would be virgin olive oil that has been found to contain various nut oils a possibly deadly combination for those with nut allergies.2

We have focused our efforts for this presentation on truffle oils. Truffles are among the most expensive foods in the world with white truffles yielding up to $14,000 per kg.3 The record price paid for a single white truffle is $330,000 that was spent on a 1.5 kg specimen.3 With such a high value coupled with a high demand it is not surprising that truffle oil was ranked in the top 10 of most frequently fraudulent foods.4

A truffle is the fruiting body of a subterranean Ascomycota fungus, predominantly one of the many species of the genus Tuber. White truffle (Figure 1) or trifola d’Alba (Tuber magnatum) comes from the Langhe and Montferrat areas of the Piedmont region in Northern Italy most notably around Alba and Asti.5,6 It is also found in Croatia, Slovenia as well as in the Drome area in France. Black Truffles (Figure 2) or black Perigord truffle (Tuber melanosporum) is named after the Perigord region in France and grows with Oak and Hazelnut trees.

Truffle oils are usually composed of virgin olive oil with a small sample of crushed truffle (usually less than 250 mg) in the bottle. The olive oil is subtle enough in flavor and aroma to not over power the truffle essence. Some manufacturers actually filter out the truffle making it even more difficult to determine if an actual truffle were used in the oil production.

The use of direct extraction Thermal Desorption GC/MS was used to determine the authenticity of several white and black truffle oils advertised as pure.

Figure 1 - White Truffle Figure 2 - Black Truffle

Materials and Methods

A total of four truffle oil samples were analyzed, two black and two white varieties. They will be identified as the following:

Sample Description

    1. Black Truffle oil origin Italy
    2. Black Truffle oil origin UK
    3. White Truffle oil origin Italy
    4. White Truffle oil origin UK

The tubes are baked out at 320ºC for four hours with a stream of high purity nitrogen passing through at 50 mL/min. The tubes are Silco coated and have a 4 mm ID. The overall dimensions of the tubes are 0.25” x 4.0”. A small aliquot (10-50 mg) of truffle oil was pipetted onto a small plug of glass wool in a preconditioned thermal desorption tube.

The Desorption tube was placed on a SIS Autodesorb 2000 thermal desorption system. (Figure 3) and a 35 mm preconditioned SS Desorption needle was attached. The ADS2000 was coupled to an Agilent 6890 GC utilizing a 5973 MSD as a mass detector. The 6890 GC had a SIS Cryotrap installed on the injector that was cooled to -45ºC with liquid CO2 to cryofocus the sample during the desorption process. The ADS2000 was programmed to allow for a 1 minute dry purge to remove any residual air from the sample. The sample was desorbed at 200ºC for a duration of 5 minutes. During the desorption process a divert valve is actuated by the desorption software and allows the injection port helium flow to pass through the desorption tube needle and into the injection port. After the desorption has concluded the divert valve switches the flow back through the GC inlet in a seamless fashion.

During the desorption the cryotrap remains at -45ºC, after the 5 minute desorption period the cryotrap is ballistically heated to 200ºC for 3 minutes and the GC/MS data acquisition is initiated. The MSD is scanning a mass range of 35-350 with a 1 second scan rate.

The GC column used in this analysis was a J&W DB-5MS (0.25 mm ID x 60M) with a 0.25 µm film and was operated at 40-250ºC with a ramp rate of 10C/minute. The GC operated in the split mode with a 5:1 split ratio. All desorption parameters were controlled by the ADS2000 software that is integrated within Chemstation program. Mass spectral data was compared with the NIST11 AMDIS software for component identification.

Results & Discussions

All four of our truffle oil samples that were tested contained significant quantities of adulterants. The most prevalent was 2,4-dithiapentane. 2,4-dithiapentane is a known aroma enhancer for truffle oil and its origin is in the refining of petroleum.4 A standard sample of 2,4-dithiapentane was run under identical experimental conditions and the impurities, heptane, octane, and DMSO were observed. Figure 4 shows the chromatogram of the Black truffle oil originating in Italy (sample #1). In addition to the 2,4-dithiapentane, there is also present heptane, octane, and dimethylsulfoxide (DMSO). Figure 5 contains the chromatogram of the black truffle oil originating from the UK (sample #2). The predominate impurity is 2,4 dithiapentane, heptane, octane and DMSO are also present but in lower concentration then in sample #1. Figure 6 pictures the chromatogram from white truffle oil from Italy (sample #3). The profile indicates the presence of heptane, octane and 2,4-dithiapentane. Figure 7 is the chromatogram from the white truffle oil sample produced in the UK (sample #4). The profile contains heptane, octane, DMSO and 2,4 dithiapentane. Also present is alpha-farnesene a sesquiterpene that is found naturally in olive oil. Alpha-farnesene was also found in all samples except for sample #3, which suggests that the Virgin olive oil in the sample is fraudulent as well.

Conclusion

All four samples tested were fraudulent as they all were advertised as pure truffle oil in virgin olive oil, but were all found to contain significant quantities (as high as 0.2%) of 2,4-dithiapentane as well as several hydrocarbons. Three of the samples (#1, 2 & 4) also contained DMSO. Sample #3 also appeared to contain at least some additional oil other than the advertised pure virgin olive oil as it did not contain the alpha-farnesene typically associated with the presence of olive oil.7

The TD/GC/MS is a valuable analytical tool to identify potential contaminants or adulterants found in food products. The ability to use a different transfer line (the desorption tube needle) with each sample eliminates the potential cross contamination or carry over associated with most thermal desorption systems.

References

    1. Food Fraud Costs Italian Farmers Billions, Italy magazine, 11-28-2007.
    2. Connecticut puts the Squeeze on Olive Oil Fraud, Diane Orson, NPR, 12, 2008.
    3. “Giant Truffle Sets Record Price” (http://news.bbc.co.uk/1/hi/world/europe/7123414.stm) BBC News. 2007-12-02.
    4. Food Fraud: 10 Counterfeit Products We Commonly Consume; Melissa Breyer, www.mnn.com/food/healthy-eating/stories/food-fraud-10-counterfeit- products-we-commonly-consume.com
    5. “White Truffles From Alba” (www.lifeinitaly.com/food/truffle.asp). Lifeinitaly.com.
    6. “Wine and Truffles Adventure-Piemonte” www.savoryadventures.com/piemonte /wine-and-truffles-adventurepiemonte.html. Savoryadventures.com
    7. Analysis of Virgin Olive Oils of Southern Italy: Chemical Composition and Sensory Attributes; Romani, A.; Pinelli, P.; Galardi, C; Mulinacci, N.; Cimato, A; Prucher, D.; Biologically-active phytochemicals in food; analysis, metabolism, bioavailability and function. Proceedings of the EUROFOODCHEM XI Meeting, Norwich, UK, 26-28 September 2001, pp. 186-189.