Driving by and smelling a behemoth wisteria plant, approximately 45 feet (15 m) high, I could not resist the temptation to sample and extract for analysis its beautiful and fragrant blossoms. As has become my custom, I photographed the plant, then used 15 g of methylene chloride to extract two whole blossoms (including stems) on-site to minimize any degradation or changes.
I am keenly aware that this method does not always hinder degradation or enzymatic changes, which can occur as soon as the blossoms are cut from the plant. Nonetheless, I have had a reliable degree of success in identifying the odoriferous components and character contributors from the blossoms using this technique.
I analyzed the concentrated samples by GC-MS T-1 shows the majority of the compounds found, with some novel results.
Interestingly, I have not found any previous literature or work identifying the following three compounds (see F-1): 6 Methoxy 4H-1-benzopyran-7-ol: C10H8O4; MW 192, 6Amino-4H-1-benzopyran-7-ol (or) 7-amino-4H-1-benzopyran-7-ol and 6,7 Dimethoxy-4H-1-benzopyran: C11H8O4; MW 206; CAS 120-08-1.
The component percentages of this extract analysis roughly reveal these odorous principles exist in the lipophilic portion of the flower, including stems. It also reveals the relatively low level of the components as they exist in the blossom. Looking at the information in this manner, one can appreciate the balance and blend along with the release of the components relative to one another.
Finding the Fragrance
Additional trace items, i.e., less than 0.05-0.01%, included: acetophenone, 3-(methylthio) propanal, vinyl guaiacol, homovanillic acid and solanone. While these chemicals are at low levels, they do significantly contribute to the aroma profile. Acetophenone and vinyl guaiacol, for example, contribute a spicy carnation and hay aroma to the overall effect. Also, the solanone (6,8-nonadien-2-one, 5-isopropyl-8-methyl-, (E)-(S)-(+)-), contributes a green and vegetable-like aroma.
The 3-(methylthio) propanal may be due to the breakdown of methionine, a naturally occurring amino acid, which I have seen in other plant extracts in previous work. This is a musty, earthy aroma that is reminiscent of potato. In my view, it is a negative aspect of the wisteria blossom and undesirable breakdown component that can be eliminated from the aroma profile with only positive effect. A component with a similar odor, 2,3-dimethylpyrazine, might be viewed in the same manner: it exhibits a powerful, earthy, potato-like character and negatively impacts the beautiful floral character of wisteria.
There also are trace amounts of beta damascone, which is a star performer in fruity tobacco with a berry aroma that envelops and beautifies any natural composition. This is routinely found in flower and fruit extracts, and keeps showing up in natural product analyses.
As I continue to examine floral and other botanicals annually, I am confident that all the materials responsible for the aroma of wisteria are not yet identified. I look forward to new discoveries as analytical sensitivity and detection improve. This, coupled with improved identification and reference spectra, make the future both interesting and exciting.