Truffle volatiles

Virtually all people lack the ability to detect some specific odors. A striking example of such an anosmia is the inability to smell the volatile steroid androsten-one (5a-androst-16-en-3-one), a constituent of perspiration, of some pork products, truffles, and celery.922... 

The volatile constituents of canned Black Perigord Truffles (Tuber Melanosporum) were analysed by dynamic headspace concentration gas chromatography - mass spectrometry. A total of 36 compounds were identified and described for the first time as canned black truffle aroma constituents. The modification of flavor and the possible formation of the compounds due to the heating treatment are discussed. 

Since cooks report that processed black truffles have a particular aroma which is different and stronger than fresh truffle aroma, we decided to investigate the volatiles of canned black truffles. 

The aim of this study was to identify the volatiles of canned black truffles by capillary gas chromatography - mass spectrometry in order to assess the modification of aroma due to the thermal processing. 

Sensory Validation of Sampling and GC Techniques. The sensory evaluation was carried out by a panel of three judges (employees of Pebeyre Ltd.). For this study, an external odor port was attached to the gas vent of the D.C.I. system. After the thermal desorption of the volatiles from the trap, the rotary valve was positioned so that the unresolved aroma isolate went to our sniffing port. The response was mesured as similarity or dissimilarity to canned black truffle aroma. 

The volatile isolate desorbed and sensorially assessed at our odor port was described as typical of processed black truffle, showing that the Tenax had adsorbed and desorbed volatile components responsible for canned black truffle aroma. 

Identification of volatiles compounds. Separate gas chromatographic - mass spectrometric analysis were made on five different canned truffles processed during the January - March 1987 period. 

A typical total ion current chromatogram of the Tenax trapped canned black truffle (Tuber Melanosporum) juice volatiles is shown in Figure 2. The compounds identified by GC-MS are listed in Table I in the order of elution from the GC column with their characteristic mass spectral data. The identification of these compounds was based on comparison of the mass spectra obtained with those stored in the NIH/EPA library and also with those of authentic compounds. Moreover, an additional search of published standard mass spectra to confirm the identity of unknowns was undertaken (16). 

The major volatile components identified in canned black truffles were alcohols and carbonyls, including acetaldehyde, acetone, 2-butanone, 2-methyl-l-propanol and the two methyl-1-butanols. Also in relatively large amount was dimethyl sulfide. 

Modification of Flavor Due to Thermal Processing. Despite the similarity of the chromatographic profiles of headspace volatiles of canned and fresh truffles, a sensory analysis carried out by a panel of experts reported a marked difference between the two aromas. 

Figure 2. Reconstructed capillary GC-total ion current chromatogram of headspace volatiles of canned black truffle (Tuber Melanosporum) juice.

Table I. Volatile compounds identified in canned Black Truffle...

The headspace technique developed in the present study to isolate volatiles from canned black truffles performed satisfactorily. The aroma isolate obtained was described as typical, and 36 compounds were identified for the first time as canned clack truffle constituents. The formation of the major part of them could be correlated to the thermal treatment applied. 

The volatile compounds in the atmosphere of cold stored Black Perigord Truffles (Tuber Melanosporum) were adsorbed onto a Tenax trap by means of a vacuum pump. The efficiency of the sampling method was sensorially validated. The volatiles eluted from the trap by heat desorption were analysed by capillary gas chromatography - mass spectrometry. A total of 26 compounds was identified. Their contribution to the final aroma impression was discussed. 

The atmosphere of cold stored Black Truffles is particularly rich in volatile compounds which impart the truffle aroma. We therefore developed a modified gas headspace sampling procedure for their isolation. 

The aims of this study were to evaluate the efficiency of our sampling method for trapping volatile components important to the aroma of Black Perigord Truffles, eind the cinalysis of minor volatiles via their identifcation with capillary gas chromatography-mass spectrometry. 

Volatile collection was generally begun the day after receiving the packages. 1000 kg of xmbrushed truffles were in storage when atmosphere capture was carried out. Three isolations were carried out in duplicate during February 1987. 

Identification of volatiles compounds A typical total ion current chromatogram of the Tenax trapped Black Truffle (Tuber Melanosporiim) volatiles is shown in Figure 4. 

The similarity of the chromatographic profiles of headspace volatiles of brushed (1,2) and unbrushed truffles (obtained in this study) allowed us to give scientific support to the informal subjective observation that unbrushed and brushed truffle aroma are not significantly different. 

Table I. Volatiles identified in atmosphere of cold storage for Black Truffles (Tuber Melanosporum)...

The headspace sampling technique developed in the present study to collect volatiles from cold stored Black Truffles performed adequately. Indeed, the aroma Isolate obtained was described as typical, and 11 minor compounds could be described for the first time as Black Truffle aroma constituents. Moreover, these results allowed the formulation of the first Nature-Identical Black Truffle aromatizer. 

Several sulfur compounds have been detected as volatile constituents of truffles. 2,4-Dithiapentane is a major component of the volatile aromatic compounds of the Italian white truffle, Tuber magnatum. Over 120 compounds have been detected in the black Perigord truffle, T. melanosporum. These include dimethyl sulfide, 2-methylbutanol, 2-methylpropanal and2-methylpropan-l-ol. The nutty and earthy flavour is attributed to anisoles and polymethoxybenzenes. Truffles also produce a volatile steroid, androst-16-en-3-one (7.67), which when more concentrated has an unpleasant smell. The combination of these compounds produces an odour that is a powerful animal attractant. The capacity of animals to detect the presence of underground black truffles by these substances has been evaluated by burying samples of the different compounds. The animals located the dimethyl sulfide lure as well as the black truffle flavouring. 

On keeping the truffle, the volatile sulfur compounds evaporate faster than other molecules. After a while, the smell becomes mushroomy and is now mainly due to l-octen-3-ol, the principal compound responsible for the smell of mushrooms (it is known as mushroom alcohol ) as well as the related l-octen-3-one, which also has a mushroom smell (see p381). 

F. Pelusio, T. Nilsson, L. Montanarella, R. TiUo, B. Larsen, S. Facchetti, and J. Madsen, Headspace solid-phase microextraction analysis of volatile organic sulfur compounds in black and white truffle aroma, J. Agiic. Food Chem. 43 2138 (1995). 

Pelusio et al. (2) studied volatiles, including organic sulfur compounds, in black and white truffles, comparing results with SPME extraction to a purge-and-trap sample preparation technique using Tenax as the adsorbent. 

In the SPME extraction method, the fiber was exposed to the headspace above the truffle sample for 30 min at either 80°C or at room temperature. In the HS Tenax adsorption procedure, thin strips of sample material were placed between plugs of glass wool in an empty stainless steel tube, which was then mounted in a desorber oven. The oven was heated to 60°C, and approximately 20 mL of He gas was used to flush the tube to the Tenax-filled cold (-40°C) trap over a 4-min period. The trapped volatiles were desorbed by rapid electrical heating to 250°C for 45 seconds and transferred to a GC column. 

Table 1 lists volatiles identified in white and black truffle aromas by head-space SPME (lOO-pm PDMS) GC/MS, and Table 2 lists results by purge-and-trap (Tenax) GC/MS. Results obtained by HS-SPME-GC/MS agreed well with those obtained by headspace Tenax adsorption GC/MS for the volatile organic sulfur compounds, and the expected discrimination of the polar or very volatile compounds by HS-SPME was confirmed. Pelusio et al. concluded that HS-SPME-GC/MS is a powerful technique for analysis of volatile organic sulfur compounds in truffle aromas, but because HS-SPME (with PDMS fibers) strongly discriminates more polar and very volatile compounds, it is less suited for quantitative analysis. 

Table 1 Volatiles Identified in White and Black Truffle Aromas by HS-SPME GC/MS...

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