Spice seasons humans as well as foods The yellow seeds from the fenugreek herb are used in the food industry as a seasoning and as an important component of curry powders but they have one conspicuous disadvantage. After they have been eaten, they exact their revenge by imparting an unpleasant odour to the consumer. Described as maple syrup, the odour manifests itself in the urine and sweat but also passes from mother to infant via breast milk. On some occasions, it has led to false diagnoses of maple syrup urine disease (MSUD), an inborn error of metabolism that is characterised by the same maple syrup odour in the sweat and urine of babies. This odour also emanates from meat and milk when fenugreek is used as a supplement to cattle feed. So, it is clear why the use of fenugreek has been limited as a food ingredient. One of the compounds thought to be responsible for the malodour is sotolon, known chemically as 3-hydroxy-4,5-dimethylfuran-2(5H)-one. This compound has been detected in the urine of MSUD patients and in the aroma profile of fenugreek, as well as burnt sugar. It has a particularly strong odour but, in itself, it cannot be held responsible for the whole aroma profile. In fact, there have been no published reports of the active aroma compounds present in human sweat and urine following fenugreek consumption, an omission which has now been corrected by a team of scientists from AgroParisTech in France. Valerie Camel, Riadh Mebazaa and Barbara Rega undertook a study of the armpit odour of two male volunteers after they had drunk infusions of crushed fenugreek seeds.

Sniffing for fenugreek The two men, who had similar diets, took samples of their own sweat before and during the fenugreek ingestion period to provide two profiles, corresponding to the normal sweat profile and the fenugreek profile. The sweat was collected using sterile gauze pads which were fixed in place in each armpit for 24 hours. Immediately after removal, the patches were halved to double the number of samples and placed in sealed vials before analysis. The odour compounds were sampled by headspace SPME using a triple-coated fibre for analysis by GC/MS and GC-O using the same column on both occasions. The polar nitroterephthalic acid-modified polyethylene glycol-coated column was selected as it provides better separation of organic acids, which the researchers anticipated would be present in the sweat. For GC-O, a panel of eight sniffing experts with previous experience of armpit sweat extracts and fenugreek extracts were employed to assess the odours as they emitted from the port. The output was split to synchronise the odours with compound detection using a flame ionisation detector. They recorded the time of each odour stimulus and noted the description, such as roast beef, pine resin, herbaceous and musty green. The data from all eight were cumulated using the frequency of detection method. The compounds were identified by GC/MS with electron ionisation, matching the mass spectra to those in the NIST mass spectral library and the retention indices to those in the Pherobase database of insect pheromones and semiochemicals.

Fenugreek aroma compounds found in sweat A total of 44 compounds were identified in sweat and the odours were described for the vast majority. They included some never previously reported for normal human armpit sweat, either in the absence or presence of fenugreek, such as nonan-2-one, isovaleric acid and 2-methyl-4-pentenal. From the total, eight compounds were associated solely with fenugreek ingestion. They were beta-pinene, 3-octen-2-one, camphor, 2,5-dimethylpyrazine, terpinen-4-ol, 4-isopropyl-benzaldehyde, neryl acetate and beta-caryophyllene. The first three compounds have been detected earlier in fenugreek seeds. 2,5-Dimethylpyrazine had the highest detection frequency with the eight panellists and is a likely candidate. Pyrazines have been reported in methanolic extracts of fenugreek seeds. However, the only zone in the chromatogram that was described as having a fenugreek odour contained a compound that could not be identified because it was below the detection limit of the GC/MS system. Given that it must possess a strong odour, the researchers speculated that it might be a metabolite of the key fenugreek odorant sotolon. Several other odour compounds remained unidentified due to low abundances or coelution, with high resolution mass spectrometry a possibility for tackling the latter. The team have suggested that odour recombination tests could be carried out to determine which particular compounds were most prominent in the characteristic odour profile. In the meantime, the maple syrup odour of human sweat following fenugreek ingestion has been partially characterised. The results will help to devise methods for reducing or eliminating the presence of this unpleasant smell. The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.