Have you ever thought that cilantro smells like a stink bug? A culinary herb and an insect that releases an odor when disturbed may seem an unlikely pair, but reading studies of their chemical composition side by side reveals molecules with the same names in both.
One is (E)-2-decenal. A molecule involved in an insect’s defensive odor also occurs in essential oil obtained from the herb’s leaves. Moreover, even for the same leaves, the compounds collected from fresh material differ from those in the essential oil. Two studies help us trace this unexpected connection.
A molecule found by two studies with different aims
The studies discussed here concern stink bugs in 2018 and coriander in 2022. Comparing their shared components is the approach taken in this article. The researchers did not conduct a side-by-side smelling test of cilantro and stink bugs.
The insect study asked whether compounds released by bugs could help locate them hidden in international freight. The plant study asked how the aroma rising from fresh leaves differed from the essential oil distilled from leaves of the same cultivars. Let us follow each question before returning to what they share.
Can stink bug odors help locate hidden aggregations?
Laura J. Nixon and colleagues studied adult brown marmorated stink bugs (Halyomorpha halys). Because aggregations formed for overwintering can become stowaways in freight, the researchers investigated whether the insects emitted detectable volatile compounds even during diapause.
The team sampled the air around undisturbed aggregations. They also prepared groups in diapause and groups whose diapause had been disrupted by changes in temperature and day length, and analyzed the compounds released after shaking their containers.
Groups that emitted defensive odors after agitation released (E)-2-decenal, tridecane, and 4-oxo-(E)-2-hexenal, among other compounds. Diapausing groups also emitted defensive odors, and were more likely to do so than the diapause-disrupted groups.
These findings suggest a possible way to locate aggregations in freight through their odors. However, tridecane, which was consistently detected, also occurs in other organisms and sources. The authors proposed looking at combinations of compounds, and identified separation from background odors and testing under real transport conditions as issues for further work.
Cilantro’s fresh leaves and essential oil present different profiles
In their 2022 study, Sunjeet Kumar and colleagues grew four cultivars of coriander (Coriandrum sativum) and examined their leaves using two methods. This is the plant used in cooking as cilantro. The study was not an analysis of the seeds used as a spice.
In one method, chopped fresh leaves were placed in a container and the air above them was sampled at room temperature. The other material was essential oil obtained by distilling the leaves for four hours. The two were compared using instruments including GC–MS, which separates and identifies components in mixtures.
It was the leaf essential oils in which (E)-2-decenal accounted for a large proportion. Across the four cultivars, it represented 15.7–25.1%. These are relative proportions based on analytical peak areas, not percentages of leaf weight or perceived odor intensity.
By contrast, (Z)-3-hexenyl acetate, associated with a green-leaf aroma, predominated among the compounds collected from fresh leaves. The fresh-leaf results table in this study does not list (E)-2-decenal. The paper therefore does not support saying that a quarter of the aroma rising from cilantro on a plate is the same compound found in stink bugs.
The researchers also tested the essential oils for radical-scavenging and antimicrobial activity, reporting differences between cultivars. These were laboratory evaluations, not studies of health benefits in people who ate the herb. The key finding for aroma is that air sampled from fresh leaves and distilled essential oil differed greatly in composition, despite coming from the same plant.
Does a shared component explain the whole odor?
Taken together, the studies identify the same molecule, (E)-2-decenal, in emissions from brown marmorated stink bugs and in essential oil obtained from coriander leaves. This is a more specific connection than simply saying that both contain aldehydes.
Two dishes need not taste the same just because they share an ingredient. A similar perspective may help with odors. What these studies establish is a chemical overlap; they did not test overall odor similarity, people’s preferences, or genetic associations. Those questions require investigating how much of each compound reaches the nose and how people respond when they actually smell the samples.
The distinction between an extract and its source plant also appears in a study comparing jasmine flowers and jasmine absolute. Understanding the difference between concentration in a bottle and concentration reaching the nose also helps reveal what a composition table alone cannot tell us.
Summary
Cilantro and stink bugs do indeed share an odor molecule. In these two original studies, (E)-2-decenal was found in emissions from brown marmorated stink bugs and in distilled essential oil from coriander leaves.
The stink bug study suggested that combinations of emitted compounds might help detect hidden diapausing aggregations in freight. The coriander study showed major differences between fresh-leaf and essential-oil composition, as well as differences in proportions between cultivars. This helps distinguish what is being examined when evaluating the aroma of a food ingredient from what is being examined when characterizing an essential oil.
The same molecule’s name appears in research aimed at detecting pests and in research aimed at understanding an herb. Findings from separate questions can reveal unexpected connections in nature.
References
- Nixon, L. J., et al. (2018). Identification of volatiles released by diapausing brown marmorated stink bug, Halyomorpha halys (Hemiptera: Pentatomidae). PLOS ONE, 13(1), e0191223. DOI and full original article.
- Kumar, S., et al. (2022). Chemical Composition of Fresh Leaves Headspace Aroma and Essential Oils of Four Coriander Cultivars. Frontiers in Plant Science, 13, 820644. DOI and full original article.
