Thursday, January 25, 2024

The Smell of Regular Things

We don't know why some things smell the way they do. What do you mean we don't know what a walnut smells like? You heat it up, run it through a gas chromatograph, and look for the spikes. Right? Not so fast. For some things, like walnuts, we didn't know how to recreate its odor without an actual walnut. Cannabis too; we all know the most easily identifiable characteristic of cannabis is it's stinky skunky odor, and yet we don't know where it comes from, down to the single molecule. 

The problem is that some odors that we identify as distinctive, indivisible, or unique are actually more than one molecule; the secret is in the ratio. In other words, the secret ingredient in the secret sauce is the recipe itself, not the ingredient:

Researchers isolate key compounds in the aroma of walnuts
Jun 2023,

As the team shows for the first time, the typical walnut aroma is created by the combination of two odorants that are present in the nuts in roughly a one-to-one ratio. The first substance is sotolon, which smells like Maggi Seasoning sauce and which, as a single component, characterizes the aroma of lovage, for example. The second compound is called (2E,4E,6Z)-nona-2,4,6-trienal. It is known from oat flakes and is responsible for the typical odor there.

British scientists had already olfactorily characterized numerous volatiles from walnuts about 50 years ago. However, none of the compounds they found had a specific walnut note. Thus, the researchers concluded that the characteristic walnut aroma is based on a combination of odorants. Despite this finding and further experiments, however, it had still not been clarified which odor-active compounds are decisive for the aroma of walnuts.

Not the components but the ratios of components -- "In our sensory tests, the walnut note intensified even further when we increased the natural concentrations of both odorants up to tenfold," reports Christine Stübner, a doctoral student who worked on the study. "However, it was important to maintain the one-to-one ratio," she continues.

(By the way, what's the purpose of all this -- based on these findings, new breeding strategies can now be developed to improve walnut aroma.) 

Finally, Instant Walnuts: Put a tablespoon of oatmeal in a glass, add a few drops of the well-known Maggi Seasoning seasoning sauce, shake it a bit and smell the mixture. (Maggi Seasoning smells like sotolon, fenugreek, hot transmission fluid.)

via Leibniz-Institut für Lebensmittel-Systembiologie (Inst for Food Systems Biology) -- Christine A. Stübner et al, Sotolon and (2E,4E,6Z)-Nona-2,4,6-trienal Are the Key Compounds in the Aroma of Walnuts, Journal of Agricultural and Food Chemistry (2023). DOI: 10.1021/acs.jafc.3c01002

A closer look at the compounds and molecules involved in giving cannabis its unique scent
Nov 2023,

(I was looking at the authors for Avery Gilbert, but no. I think some rec ognition is in order; he was the first to conduct smell research on cannabis.)

Using mass spectrometry, gas chromatography and flame ionization detection, researchers found that a molecule called 3-methyl-2-butene-1-thiol (321MBT), along with other volatile sulfur compounds (VSCs), appeared to play a prominent role in odor production. 321MBT is the same molecule that gives warm beer and skunk spray their distinctive smells. 

via terpene distributor Abstrax Tech: Iain W. H. Oswald et al, Minor, Nonterpenoid Volatile Compounds Drive the Aroma Differences of Exotic Cannabis, ACS Omega (2023). DOI: 10.1021/acsomega.3c04496

Research team identifies human odorant receptor for 'horse stable' odor, with implications for food testing
Aug 2023,

Para-cresol (4-methylphenol) is an aromatic compound with a strong horse stable-like odor, it is formed during the microbial degradation of certain amino acids, but also during thermal degradation processes, it's also a characteristic odorant in whiskey and tobacco.

  • The OR9Q2 receptor was the only one that responded to physiologically relevant concentrations of the substance.
  • Conversely, 4-ethylphenol was the only one of 176 aromas able to significantly activate the receptor. (and that's called being highly selective).
  • "The receptor fills a gap in the recognition spectrum of the phylogenetically older human odorant receptor OR2W1, which detects a wide range of structurally different odorants, but not para-cresol."

via Leibniz-Institut für Lebensmittel-Systembiologie aka Leibniz Institute of Food Systems Biology at the Technical University of Munich: Franziska Haag et al, The multi-faceted food odorant 4-methylphenol selectively activates evolutionary conserved receptor OR9Q2, Food Chemistry (2023). DOI: 10.1016/j.foodchem.2023.136492

Thursday, January 18, 2024

Electronic Hedonics

Electronic noses sniff out volatile organic compounds
May 2023,

Many e-noses generate different signals toward VOCs of the same concentration when the sensor is located in different parts of the "nose" chamber:

"To counteract this problem, the fluidic behavior of the gas flow needs to be well controlled," said author Weiwei Wu. "This ensures a uniform fluidic field and concentration of VOCs in the chamber and avoids generating any fake sensing characteristics."

A vertical chamber that looks much like a showerhead promotes vertical flow so gas spreads through holes at the bottom of the device and around to evenly distributed sensors.

via Interdisciplinary Research Center of Smart Sensors, School of Advanced Materials and Nanotechnology, Xidian University; Intelligent Perception Research Institute, Zhejiang Lab, Hangzhou: Controlling fluidic behavior for ultrasensitive volatile sensing, Applied Physics Reviews (2023). DOI: 10.1063/5.0141840

Note: This problem has come up in two other papers where they talk about how the two different nostrils cancel each other out because they can't rely on evenly distributed air; it messes up the statistics, so at least with two different nostrils, you can have some error correction. See "Domestic cat nose functions as a highly efficient coiled parallel gas chromatograph", We et al. PLoS Computational Biology (2023). DOI: 10.1371/journal.pcbi.1011 and "Odor representations from the two nostrils are temporally segregated in human piriform cortex", Dikeçligil et al, Current Biology (2023). DOI: 10.1016/j.cub.2023.10.021

Perceiving the smell of lemon, geranium or eucalyptus: A study on the electrical signals behind human olfaction
Jul 2023,

Somewhat related to electronic noses, real-live odor receptors obtained from nasal biopsies:

"Until now, nobody had measured in intact human tissue the electrical activity of cells, neurons and epithelial cells that form the olfactory epithelium of our nose in which odorant molecules are captured."

via International School of Advanced Studies, Aldo Moro University of Bari, University of Trieste, and the Otorhinolaryngology Clinic of Azienda Sanitaria Universitaria Giuliano Isontina: Andres Hernandez-Clavijo et al, Shedding light on human olfaction: electrophysiological recordings from sensory neurons in acute slices of olfactory epithelium, iScience (2023). DOI: 10.1016/j.isci.2023.107186

'Electronic tongue' holds promise as possible first step to artificial emotional intelligence
Oct 2023,

It sounds to me a bit of a stretch right now to call this emotional intelligence; it sounds like basic chemical detection to me, but with the addition of a memristor.

The memristor is the new part, and one day we will have gustatory chips, and olfactory chips, vision chips, etc.; chips for everything; everything will have its own chip. Christmas chips and new mother chips and traffic chips for cars and ambient energy harvesting chips for sneakers and even organic chemistry chips for med students so they don't have to study. Everything will have its own chip. There won't be categories of chips, instead every single thing will have its own chip. Just not today. 


The artificial tastebuds comprise tiny, graphene-based electronic sensors called chemitransistors that can detect gas or chemical molecules. The other part of the circuit uses memtransistors, which is a transistor that remembers past signals, made with molybdenum disulfide. This allowed the researchers to design an "electronic gustatory cortex" that connect a physiology-drive "hunger neuron," psychology-driven "appetite neuron" and a "feeding circuit."

"When detecting salt the device senses sodium ions. This means the device can 'taste' salt."

"We are trying to make arrays of graphene devices to mimic the 10,000 or so taste receptors we have on our tongue."

via Penn State: Subir Ghosh et al, An all 2D bio-inspired gustatory circuit for mimicking physiology and psychology of feeding behavior, Nature Communications (2023). DOI: 10.1038/s41467-023-41046-7

Thursday, January 4, 2024

Smells Throughout History

Proof that part of the Roman Empire smelled of patchouli
May 2023,

Two thousand years ago, in the Roman city of Carmo (today's Carmona), in the province of Seville, someone placed a vessel of ointment in a funerary urn. A small hyaline quartz rock crystal flask, carved in the shape of an amphora, contained the ointment.

The ointment was preserved because of the Dolomite used as a stopper, and the bitumen used to seal it.

Two components of the perfume have been identified: a base or binder, which allowed for the preservation of the aromas, and the essence itself; these findings according with descriptions by none other than Pliny the Elder. The base was a vegetable oil, possibly olive oil. The essence was of patchouli, widely used in modern perfumery, but whose use in Roman times was not known. 

via University of Córdoba: Daniel Cosano et al, Archaeometric Identification of a Perfume from Roman Times, Heritage (2023). DOI: 10.3390/heritage6060236

Unbottling the scent of the afterlife: New study of ancient Egyptian mummification balms
Aug 2023,

They used gas and liquid chromatography to reconstruct mummification substances, i.e., balm residues, found in two canopic jars from the mummification equipment used to embalm the noble lady Senetnay in the 18th dynasty, circa 1450 BCE.

The team found that the balms contained a blend of beeswax, plant oil, fats, bitumen, Pinaceae resins (most likely larch resin), a balsamic substance, and dammar or Pistacia tree resin.

Working closely with the French perfumer Carole Calvez and the sensory museologist Sofia Collette Ehrich, the team meticulously recreated the scent based on their analytical findings.

(Sensory museologist: exists)

via the Max Planck Institute of Geoanthropology and Moesgaard Museum in Denmark: Barbara Huber, Biomolecular characterization of 3500-year-old ancient Egyptian mummification balms from the Valley of the Kings, Scientific Reports (2023). DOI: 10.1038/s41598-023-39393-y.