Truffles (Tuber spp.) are part of the ascomycota phylum of the fungi kingdom and are found underground, growing as symbionts with specific trees by forming ectomycorrhizae [1]. They are highly prized by local people and food connoisseurs worldwide, for the unique aromas they add to dishes. However their cultivation is hard to control and depends on many factors such as soil conditions, temperature, humidity, surrounding flora and fauna [2]. Hence truffles are amongst the most expensive foodstuffs in the world, reaching prices from 600€ to 6000€ per kilogram in 2006 [3]. Tuber magnatum (white truffle) is considered to have the most complex aroma and is hence more expensive compared to T. melanosporum (black or Périgord truffle) and T.aestivum (summer truffle). The latter being the least flavoursome and more readily available truffle [4]. These three most common truffles in Europe are mainly found in Mediterranean regions, notably Italy, France and Spain [5,6] and they are also the most studied (3). Some truffles have had their aromas characterised. However this is no easy task as the aromas were found to be specific to a species and influenced by many factors: geographical origin, maturity, hydration, and storage conditions of the truffle for example. For example bis(methylthio)methane (also known as 2,4-dithiapentane) is a key compound in the aroma of T.magnatum and dimethylsulfide (DMS) in all black and summer truffles. More specifically 2- and 3-methylbutanal are characteristic of T.melanosporum and B-phenylethanol of T.aestivum. Aromas are made of volatile organic compounds and HS-SPME-GC/MS (Headspace-Solid Phase Microextraction-Gas Chromatography-Mass Spectrometry) is a technique that has proved useful in their identification [7]. Sampling from the headspace of a vial ensures only the volatile compounds are taken into account. SPME is a solvent-less extraction process that allows an easy transfer of these volatiles from the vial to the GC/MS as they adsorb onto a fused silica fibre coated with polymers of different polarities. The sample then passes through the GC column carried by a constant flow of helium and compounds separate. The MS finally produces a spectrum for each isolated fraction. The identification of analytes then relies on a simple process: the analysis of a mass spectrum from each peak in the gas chromatograph and retention indices. GC⁄MS instruments are less sensitive than the human nose [8] but the technique is simple, fast, requires very little sample preparation, will incur no sample modifications during its use, and provides accurate, reproducible results. Having strong aromas, truffles are ideal candidates for HS-SPME-GC/MS analysis. The aim of the study was thus to identify molecules characteristic of a truffle species (black T.melanosporum, summer T.aestivum, and white T.magnatum) in the aroma of various natural and artificial truffle products. The efficacy of these products to mimic the aromas of raw truffle was assessed from these results. For every SPME analysis 1 g of sample with 500 µL of water (purified with the milli-Q system) were measured into a vial (20 ml), and a magnetic stirrer added. A PTFE-silicon septum was used to close the vial and make it air-tight. The vial was heated under stirring at around 1300 rpm until the equilibrium temperature was reached. The fibre was then exposed to the headspace of the sample for a determined extraction time. Once the extraction time had ended the fibre was removed from the vial and placed in the injection port of the gas-chromatogram. A desorption time of 15-20 min was adequate to desorb most of the analytes from the fibre in all conditions. After desorption from the fibre, the extract was directly transferred to the analytical column. The fibres were cleaned daily to prevent contamination. Cleaning was done by performing a blank GC-MS run with the same conditions. It was found that the analysed samples whether naturally or artificially produced, were not able to adequately replicate the aromas of the species of truffle stated. Oils made with the natural aromas or extracts of truffle did not transmit many characteristic VOCs, nor in similar amounts. The artificially made oils and sauces were mainly dominated by bis(methylthio)methane. This was not always appropriate for the species of truffle stated on the labels. It was also found that one artificial white truffle aromatised oil aroma seemed to mimic the profile of black truffles more.

Volatile profile characterization of truffle oils and natural aroma products by HS-SPME-GC-MS

G. Sagratini;S. Vittori;G. Caprioli;
2015-01-01

Abstract

Truffles (Tuber spp.) are part of the ascomycota phylum of the fungi kingdom and are found underground, growing as symbionts with specific trees by forming ectomycorrhizae [1]. They are highly prized by local people and food connoisseurs worldwide, for the unique aromas they add to dishes. However their cultivation is hard to control and depends on many factors such as soil conditions, temperature, humidity, surrounding flora and fauna [2]. Hence truffles are amongst the most expensive foodstuffs in the world, reaching prices from 600€ to 6000€ per kilogram in 2006 [3]. Tuber magnatum (white truffle) is considered to have the most complex aroma and is hence more expensive compared to T. melanosporum (black or Périgord truffle) and T.aestivum (summer truffle). The latter being the least flavoursome and more readily available truffle [4]. These three most common truffles in Europe are mainly found in Mediterranean regions, notably Italy, France and Spain [5,6] and they are also the most studied (3). Some truffles have had their aromas characterised. However this is no easy task as the aromas were found to be specific to a species and influenced by many factors: geographical origin, maturity, hydration, and storage conditions of the truffle for example. For example bis(methylthio)methane (also known as 2,4-dithiapentane) is a key compound in the aroma of T.magnatum and dimethylsulfide (DMS) in all black and summer truffles. More specifically 2- and 3-methylbutanal are characteristic of T.melanosporum and B-phenylethanol of T.aestivum. Aromas are made of volatile organic compounds and HS-SPME-GC/MS (Headspace-Solid Phase Microextraction-Gas Chromatography-Mass Spectrometry) is a technique that has proved useful in their identification [7]. Sampling from the headspace of a vial ensures only the volatile compounds are taken into account. SPME is a solvent-less extraction process that allows an easy transfer of these volatiles from the vial to the GC/MS as they adsorb onto a fused silica fibre coated with polymers of different polarities. The sample then passes through the GC column carried by a constant flow of helium and compounds separate. The MS finally produces a spectrum for each isolated fraction. The identification of analytes then relies on a simple process: the analysis of a mass spectrum from each peak in the gas chromatograph and retention indices. GC⁄MS instruments are less sensitive than the human nose [8] but the technique is simple, fast, requires very little sample preparation, will incur no sample modifications during its use, and provides accurate, reproducible results. Having strong aromas, truffles are ideal candidates for HS-SPME-GC/MS analysis. The aim of the study was thus to identify molecules characteristic of a truffle species (black T.melanosporum, summer T.aestivum, and white T.magnatum) in the aroma of various natural and artificial truffle products. The efficacy of these products to mimic the aromas of raw truffle was assessed from these results. For every SPME analysis 1 g of sample with 500 µL of water (purified with the milli-Q system) were measured into a vial (20 ml), and a magnetic stirrer added. A PTFE-silicon septum was used to close the vial and make it air-tight. The vial was heated under stirring at around 1300 rpm until the equilibrium temperature was reached. The fibre was then exposed to the headspace of the sample for a determined extraction time. Once the extraction time had ended the fibre was removed from the vial and placed in the injection port of the gas-chromatogram. A desorption time of 15-20 min was adequate to desorb most of the analytes from the fibre in all conditions. After desorption from the fibre, the extract was directly transferred to the analytical column. The fibres were cleaned daily to prevent contamination. Cleaning was done by performing a blank GC-MS run with the same conditions. It was found that the analysed samples whether naturally or artificially produced, were not able to adequately replicate the aromas of the species of truffle stated. Oils made with the natural aromas or extracts of truffle did not transmit many characteristic VOCs, nor in similar amounts. The artificially made oils and sauces were mainly dominated by bis(methylthio)methane. This was not always appropriate for the species of truffle stated on the labels. It was also found that one artificial white truffle aromatised oil aroma seemed to mimic the profile of black truffles more.
2015
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11581/407283
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