Sweet-smelling vanillin lies at the heart of vanilla aroma. Yet comparing vanilla beans reveals different facets, including smokiness and an anise-like spiciness. A 2016 study compared three samples from Madagascar, Comoro, and Tahiti to investigate minor compounds associated with these differences.
In every sample, vanillin remained detectable through the greatest dilution. Alongside it, anise-related compounds stood out in the Tahiti sample, while smoky guaiacol provided an important clue in the Comoro sample.
Comparing three samples by smelling them through successive dilutions
The researchers used one commercial vanilla-bean product from each origin. The Madagascar and Comoro beans belonged to Vanilla planifolia, and the Tahiti beans to Vanilla tahitensis. The Madagascar sample was harvested in 2010 and the other two in 2011.
Combining solvent extraction with high-vacuum distillation while avoiding excessive heating, the researchers prepared aroma concentrates that retained the characteristics of the original samples well. They diluted these in fourfold steps and examined them by AEDA, a method in which people smell compounds as they are separated by an instrument.
The FD value indicates the greatest dilution at which a compound’s odor remained detectable. The researchers used the dilution level detected by at least two of three assessors. FD values help identify potentially important odorants, but they are neither compound concentrations nor measures of the overall intensity of vanilla aroma.
There were 49 odor-active peaks, of which 36 were identified or tentatively identified. The nine compounds newly reported in vanilla included tentative identifications, and some odors remained unidentified.
Shared vanillin, different supporting compounds
Vanillin had the highest FD value in all three samples. Beyond that common feature, the combinations of other compounds revealed characteristics of each sample.
The Madagascar sample was described as fatty and whisky-like. Unsaturated aldehydes with sweet, fatty odors had higher FD values than in the Comoro sample.
The Comoro sample had a characteristically smoky aroma. Apart from vanillin, guaiacol, with its burnt odor, had a particularly high FD value and was considered relevant to that character. Even within planifolia, the combination of compounds was not uniform.
The Tahiti sample had a spicy, anise-like aroma. Four compounds had characteristically high FD values: anisaldehyde, anisyl acetate, anisyl alcohol, and isovanillin. These included compounds contributing not only sweetness but also cherry-like and spicy qualities.
Differences in where a molecular group is attached
Alongside comparing aromas, the study examined the structures and amounts of characteristic aromatic compounds. It focused on the position at which a methoxy group was attached to the molecular ring.
In the two planifolia samples, vanillin and eugenol, which have a methoxy group at position 3 under the paper’s numbering convention, were relatively abundant. The Tahiti sample tended to contain more compounds with the group at position 4, including anisyl alcohol, anisaldehyde, and isovanillin.
The semiquantitative values for anisyl alcohol were 8 µg/g for Madagascar and 6 µg/g for Comoro, compared with 1,175 µg/g for Tahiti. Vanillin values were 6,201, 8,053, and 1,501 µg/g, respectively: it was present in Tahiti, but at a lower value than in the other two samples. These are semiquantitative values based on instrument responses relative to an internal standard, not percentages of aroma contribution.
From this structural pattern, the authors considered possible differences in the activity of methylating enzymes that produce methoxy groups and in biosynthetic pathways. The study did not measure enzyme activity or genes, however; this was a hypothesis based on the compound profiles.
Avoiding assumptions based on origin alone
The authors also suggested that processing conditions, including curing and drying, microorganisms, and maturity at harvest might contribute to the differences. For example, conditions during processing might have influenced the abundance of guaiacol in the Comoro sample.
Only one product from each origin was compared, however, and species, harvest year, growing conditions, and production conditions were not individually controlled. Many more products would need to be compared before concluding that all Tahitian vanilla has a particular ratio or all Comoro vanilla has the same aroma.
Nevertheless, the study showed that combinations of minor odor-active compounds, which a comparison of vanillin alone would miss, can provide clues to distinctive character.
Summary
Vanillin had the highest FD value in all three samples. Different combinations accompanied that shared sweet center, including fatty aldehydes in Madagascar, smoky guaiacol in Comoro, and anise-related compounds in Tahiti.
The Tahiti sample also contained greater amounts of compounds with particular structural features, such as anisyl alcohol. The study illustrates that understanding differences in vanilla requires looking beyond the main compound to substances perceptible at low levels and to how they are produced.
All three authors listed Ogawa & Co., Ltd. as their affiliation at publication. No separate funding or conflict-of-interest declaration section was identified.
References
Shigeto, A., Hachisuka, S., & Kumazawa, K. (2016). Characterization of Potent Odorants in Three Different Cultivars (Madagascar, Comoro and Tahiti) of Vanilla Bean by Aroma Extract Dilution Analysis (AEDA). Food Science and Technology Research, 22(6), 811–816. doi:10.3136/fstr.22.811 (Full original article)
