Friday, July 12, 2024

Nose Diving

The year 2020 was momentous. There was a global pandemic that killed millions of people and brought the world to a standstill for about a year. So most of us completely missed the release of Harold McGee's book, which is absolutely, with no hesitation, and nothing to even compare it to, the greatest and most important book ever written on the topic of smell. 

This person, Harold McGee, is already very well known for his 1984 book On Food and Cooking, which made him a legend of the culinary world. On Food is considered a Bible, if not the Bible, of cooking. He was the first person to look at food and cooking as a scientist. But he's not a scientist. He's not a chef either. He's just a really, really good writer.

When I heard that he was writing another book, this time about smells, I had to make sure it was the same person - this can't be true, not him. Personal note - I also wrote a book about smells, in 2015. I tried really hard to make sense out of the way we talk about the things we smell. I failed. But if there was ever a person that could do what I wanted to do, it was him. I read On Food back around 2010 when two of my closest friends were both going to cooking school. In fact, I had just finished reading it a second time circa 2020, thinking maybe I had learned enough about chemistry in the intervening years to help me digest the more technical parts of this seminal work. 

After I learned of his forthcoming book, but before it was released, I had hopes, but they weren't too high. Smell is too hard. There's just too much there to make sense of it, and for a lot of reasons, we're almost hardwired to NOT make sense of it. I thought it would be more like a primer, a survey, and introduction, a teaser. He certainly can't do to smell what he did to food and cooking. Nobody can. 

Then I read the book. It took me two years; I read every single word, including the notes, and some parts I read twice. But it didn't take long for me to realize what he had done. He wrote the most important book on smell ever written. I know it sounds like hyperbole, but it's not. The last time I checked, which was about 2015ish, there were about 30 books in the Library of Congress on the topic of smell. There were 300 books on perfume bottles, and 30 books on smell. People just don't write about it.

To say that McGee wrote the most important smell book ever is not an exaggeration; but the other side of the truth is that there aren't many books to compare it to. And of all the books that are written about smells, none of them tackle the language of smell (except my attempt, Hidden Scents). Ann-Sophie Barwich does a pretty good job with her 2020 book on the philosophy of smell, but even she avoids some of the messiest parts of olfactory perception, that being the language we use to talk about smells. (Here's my review)

I will cut short my praise and leave one final note, mostly out of personal interest - a fragrance friendly organization called The Perfumed Plume nominated this book Nose Dive alongside a coffeetable compendium by Gestalten called The Essence: Discovering the World of Scent, Perfume and Fragrance for the 2020 Fragrance Book of the Year. I wrote a couple chapters for The Essence. Needless to say, Nose Dive won. Actually, in the end, the pandemic won, because mostly nobody anywhere was paying attention to any of this at the time.

(^cool illustrations explaining how smells work via biology)

Nose Dive: A Field Guide to the World's Smells
Harold McGee, Penguin, 2020

--see below a note on punctuation "*"
--"osmcosm" (the universe of smells) pxi
--"original volatiles" are birds because volatile means "to fly" pxii
--"The smell of a person's body ... is the body with the flesh removed" -Sartre pxx; meaning the smell is the vaporous molecules, not the substance of the flesh
--"minerality", mineral, mine - smell of moist stones, used in wine-tasting but not the smell of actual minerals which come from inside the earth where it smells like sulfur p23-24
--First, on Earth, life ran on iron and sulfur, then oxygen. Today, some of us, our cells, still run on iron and sulfur, and so oxygen is toxic p25
--"sulfidic" p37
--"catty" cat ketone p80-81
--skin aldehydes Japanese kareishu, nonenal p112
--Essay: Olfactory Comfort in Close Relationships: You aren't the only one who does it, by Donald McBurney, 2014 p125
--The confusion is the very nature of plants and in the way we perceive smells. Plants deposit countless different molecules in their wood and leaves and flowers and fruits because they can. The smell of any particular item is a composite of many different volatiles, of which perhaps a dozen or two predominate. So several different molecules can remind us of the same item. And then on our end, we encounter many of the same molecules in different plants: so one molecule can remind us of several different items. In fact, that's part of the interest of paying close attention to flavor. When we do, we notice echoes and rhymes in many different things. p142
--Plant Metabolic Highways, see charts on page 150 and 152
--on terpenes, again, because we are usually exposed to many of them all at once and from the same source, we *encode* them ambiguously, and so when we try to *decode* them, we get mixed up. p164
--"Plants are profligate chemists" p186
--stinking goosefoot has a "fishy, ammonia-like smell due to an unusual stockpiling of trimethylamine - hence vulvaria, "vulva-like," for the supposedly similar smell of female genitalia (see p116) p203
--The creosote bush, Spanish name hedionilla, from heder, "to stink" (hedione?) p204
--On Flowers and Smell: volatile and pigment molecules share biochemical resources, so that more color means less scent, in part because some scent volatiles are also plant hormones that shorten vase life p211
--Corn salad or mâche, small spinach-like rosette, called lamb's lettuce, a mix of John Milton's garden of Eden and valerian; unlike any other salad green p247
--cilantro - similar culantro, in the celery family, popular in Southern Asia and Mexico, despised elsewhere, described as soapy. "This difference in taste is likely due to genetic differences in sensitivity to the volatiles, cultural differences in exposure to them, and also t their unusual nature. They're neither terpinoids nor benzoids, the usual herb volatiles, so they don't immediately suggest aromatic plants, instead, these aldehydes are commonly encountered in everyday life as breakdown fragments of a the long-chain lipids in soaps and cosmetics: materials that are inedible and distasteful. They're also emitted by various insects, including stinkbugs." p258
--Harold McGee is one of the few people who can start out as a layperson, but through the process of writing, rises to the level of scientist, but while maintaining his lay-language. His writing is so effortless to read, and yet so crystal clear in what it's trying to say, that you are immediately smarter by the end of the sentence. He also has the determination, and the ability, to follow every one of the paradoxes and conundrums the plague the field of olfaction, like the way he describes the Cilantro Problem [above] Part geneticist, part cultural anthropologist, food chemist, flavor chemist, and finally entomologist. Oh, etymologist too, sure.
--This "field guide" takes you to a global grocer featuring every odiferous organism possible, neatly arranged (so neatly arranged) in rows and stands, and all available for us to smell them, albeit only by the words we call them and the names of their molecules. (p266)
--He states that while trying to do his research, "Surprisingly, I haven't found any published studies of raw corn kernels or grits or flour." p276 Note that he has found studies on about a thousand other things, so it's not like he doesn't know what he's doing. Just weird. (And I'm looking at you Big Corn, all that glyphosate, biofuel, whatever. Remove the research remove the competition.)
--methyl sulfyanylhexanol is in passionfruit and underarm sweat p301
--citron is so terpentine-y that Greeks associated it with cedar and juniper p320
--"strawberry furanone" = "pineapple ketone" p331
--Finishing the fruit chapter with Durian: Most plant volatiles are defensive warnings and weapons, but by controlling our exposure to them, we manage to enjoy the sensation they stimulate - so much so that we volunteer to protect them ourselves. p335
--he refers to geosmin as an "olfactory landmark", sort of a way of organizing odor networks. p348
--octenone, a ketone, metallic and bloodlike, generated by reactive metals from keys and coins, etc. p350-351
--When he introduces terms, he often provides disambiguating context: "To students of the fungal kingdom, mushrooms are "fruiting bodies". And he goes on to explain how mushrooms are like fruit. He is a master teacher. p352
--melons, cucumbers and mushrooms all smell like fish, because fish (and oysters etc) were the first to emit these volatiles hundreds of millions of years before melons p382
--merior is terrior but for the sea, like the tastes of oysters p392
--The volatiles of squid, cuttlefish and octopus have "next to nothing" of research p395
--Toxic smell p401 (add to IH notes)
--Vanilla and clove smell like smoke (not vice-versa, like fish and melons), they are similar to guaiacol, and lignin breaks into vanillin and eugenol in fire (and in people) p412-413
--He calls fossil fuels fossil organics, because they instigated so much of our understanding p419
--He doesn't call benzene "aromatic" but "solvent" and "sweet" p421
--"The volatiles of modern materials," a section between the end of the book, in the chapter on Smoke, Asphalt, and Industry, he describes the smells of polystyrene, rubber, Bakelite, carpets, auto tires, 3-D printers, polyethylene water bottles and food wraps. It's probably the craziest chapter, and section, in the whole book. 
-"I smell it as I type paragraph when I sniff through the keyboard of my warm laptop computer." (Bakelite-like circuit boards)
-"One polymer often used in screwdriver handles (celluloste acetate butyrate) is notorious for breaking down into vinegary and cheesy acetic and butyric acids that accumulate in the toolbox."
-"To this day I sniff pre-packages sandwiches before I buy them." p428-499
--In addition to the common tree-wood volatiles, rotos have unique sesquiterpenoids, probably to defend against soil microbes - shyobbunones, acorenone, costols, and zizaenones appear nowhere else in this book. p463
--In India, wild khus roots (like vetiver) are woven into shades and mats that are sprinkled with water to cool and scent the air. p463
--musks - "animal protein machinery" by-products, "not especially unpleasant but they do get our attention, subliminally or overtly. A touch of musk or beaver is a way of asserting the wearer's animal presence by prestigious proxy rather than poor hygiene: a refined means of visceral communication." p465
--synthetic "white musks" are used for a "hot-iron-on-fresh-laundry" quality - the opposite of the original musk's underside-of-wild-mountain-creature quality! The rare, strange, ambivalent animal materials became a stepping stone to the ubiquitous reassurance of domesticity and cleanliness. p475
--Hedione is named in a chart on p475, the molecule methyl dihydrojasmonate, c.1960, smells like fresh, floral, "transparent," "over-ripe lemons"; and was found later in black tea 1974, and jasmine osmanthus, lima sweet orange p475 (?)
--Hedione again: Edward Roudnitska's Eau Savage, "Wild Water" added to an eau de Cologne citrus-herb mix the newly discovered Hedione and its fresh, bright, "transparent" volatility, which soon became a standard ingredient in modern perfumes. (p475?)
--Monko, or listening to smells (Japanese); It can be exhilarating to listen to beautiful or strange aromatics. It's also exhaustingly inward to focus on the invisible and intangible, and rack the memory for precedents or comparables. But it's building a database, and nose and a sensory work. p483 [he's referring then to the smell lexicon as a "database"]
--He doesn't talk about foods until Chapter 18 Cooked Foods. p484
--The combinatorial code of food: Liebniz Institute for Food Systems Biology near Munich, 2014, Peter Schieberle, Thomas Hofmann, and colleagues reviewed several decades of work and reported that only 230 molecules account for the majority of important volatiles in a wide range of foods, and that any given food aroma can be reasonably simulated with about a dozen of these key molecules in specific proportions. This "combinatorial code"; I assume this is the reference: A Dunkel, M Steinhaus, et al. (2014). Nature's chemical signatures in human olfaction: A foodborne perspective for future biotechnology. Angewandte Chem Int Ed 53: 7124-7143 [key food odorants] 
--Thai scented candle dessert - tian op, beeswax, incense, benzoin, frankincense, sandalwood, citrus peels, herbs, spices, essential oils, even musk p493
--Blood - we usually describe the smell as "metallic" because it's similar to the smell left on our fingers when we handle coins, or in the air when we scrub a bare metal pan or sink. But metals themselves aren't volatile: we're actually smelling the fragments created when stray heme iron and other metals help oxygen attack the carbon chains in our cell membranes, skin oils, or dish soap. Polyunsaturated chains, kinked at several points by double bonds between adjacent carbon atoms, are the most successful metallic-smelling. In the case of blood and exposed surfaces of raw meat, the key fragment is a ten-carbon, one-kink aldehyde with an oxygen atom riding its middle:an epoxy decenal (also see octenone, nonenone ,octadienone, hexenone, heptanone, nonenol) p502-503
--Olfactory Camouflage - force-feeding birds, castrating hogs, and grain-feeding cattle are all venerable versions of a kind of olfactory camouflage, a pre-cooking on the hoof that emphasizes generically fatty smells over the specifically animal and bloody p506; and this is because livery-ness in game meats and grass-fed cattle, because animals that live on open pasture take lots of multi-kinked carbon chains from whole plants, but are otherwise lean, so their metallic fragments are prominent p505
--Cooked fish bouquet - geranium leaf and cooked potato (methional and octadienone) p507
--Distinctly fishy - when fish or shellfish are less fresh or cooked more thoroughly, the long exposure to oxygen or to heat energy breaks their kinked chains mainly into seven- and ten-carbon fragments, - and this is the mix that smells distinctly fishy p507 ["distinctly fishy" just sounds funny]
--Lovage and the "Maggi plant" - many main dishes in the European tradition begin with the preparation of a base of "aromatic" vegetables (onion, carrot, celery) [~p507-512?]
--MMP gene - German flavor chemists in 2009 and 2011 published major volatiles of meat stews. The dominant "gravy-like"note came from onions and leeks being chopped and then heated, for both chemical and heat enzymes to break them into mercaptomethyl pentanol (MMP). ... MMP activates a receptor from Neanderthals which he calls "sweat-adjacent", suggesting this highly sensitive single receptor may have been about human sweat p512-513 
--rancid oils and stale food charts! p537-538
--"sweaty salty feet" - is a close relative of the Brevibactererum that ferments brine-washed Epoisses and Limberger  and makes it orange, also related to salt water sediment and fish p550
--Pseudofermentation - [my term - true pickles vs acid pickles] true pickles are fermented, modern pickles are "manufactured by simple acidification" p552
--The Industrial Approximation of Soy Sauce - soybeans pressure cooked with strong hydrochloric acid, generates an aroma surprisingly similar to the fermented version p558; see chart: fermented vs acid hydrolyzed p559
--smells like vomit - pecorino romano is a sheep's milk cheese coagulated with the protein-and-fat-digesting-enzymes in an extract of lamb stomach, so it's rich in butyric and sweaty fatty acids [smells like vomit] (and when aged, it smells like pineapple, ie ethyl butyrate, from the butyric acid) p568
--Arcaridial is an unusual molecule, found in the rinds of aged mimolette, which develop colonies of mites that leave behind a powder that smells fatty-nutty or "surprisingly good" for spider pheromones p569
--Fruit fly taint - female drosophila carry a wax-floral aldehyde as a pheromone to attract males, and can leave a detectable off-odor in the [wine] glass within minutes p575
--Hefewizen is banana-like p578
--Japanese buckwheat shochu is a rare grain [rice] spirit without long aging p589
--Yeast travel on insects, and came before flowers p591-592
--In the conclusion he says the tables of molecules and notes "only indicate notes that you may perceive in the overall smells of things. They're not prescriptions for what you should perceive. Smell perception simply isn't prescribable, for reasons that would fill another book." p595 [ahem]

*I vacillate between American and British punctuation with the quotations and commas, apologies.

Thursday, March 7, 2024

Hyperdimensional Navigation Syndrome


How humans use their sense of smell to find their way
Oct 2023,

28 participants each entered a virtual three-dimensional smellscape four times. The placement of eight "odor objects" in the environment (smells like orange or banana) always stayed the same. What changed was where participants were placed in the virtual reality arena and which target odor they needed to find.

Results? "Human subjects can actually navigate spaces using their nose in the context of a particular type of virtual reality environment."

"We also demonstrated that this behavior was associated with the emergence of a particular neural signature indicative of what we might call 'cognitive maps.' This neural signature not only appeared in areas traditionally associated with navigation behavior, but also in olfactory-related brain regions."

Their findings suggest that these two sets of brain regions share a common spatial code, something that hadn't previously been known.

via University of Pennsylvania Jay Gottfried's lab: Clara U. Raithel et al, Recruitment of grid-like responses in human entorhinal and piriform cortices by odor landmark-based navigation, Current Biology (2023). DOI: 10.1016/j.cub.2023.06.087

Thursday, February 29, 2024

Chromatic Classification of Odor Identities

Scientists are smart - the way they figured this out is really clever, because they literally "blinded" the participants to the study; they're not asking you to tell them what color comes to mind, they ask you to just choose the neutral gray. This is how they figure out racial bias too:

Our sense of smell alters the colors we see, show scientists
Oct 2023,

"In a previous study, we had shown that the odor of caramel commonly constitutes a crossmodal association with dark brown and yellow, just like coffee with dark brown and red, cherry with pink, red, and purple, peppermint with green and blue, and lemon with yellow, green, and pink," explained Ward.

Ward and colleagues tested 24 adult women and men between 20 and 57 years of age with one of six odors chosen at random from caramel, cherry, coffee, lemon, and peppermint, plus odorless water as a control, and asked to manually adjust two sliders - one for yellow to blue, and another for green to red - to change its color to neutral gray. 

Participants had a weak but significant tendency to adjust one or both of the sliders too far away from neutral gray. For example, when presented with the odor of coffee, they wrongly perceived 'gray' to be more of a red-brown color than true neutral gray. 

An exception was when the odor of peppermint was presented: here, the participants' choice of hue was different from the typical crossmodal association demonstrated for the other odors. As expected, the participants' selection likewise corresponded to true gray when presented with the neutral scent of water. 

via John Moores University in Liverpool: Ryan J. Ward et al, Odors modulate color appearance, Frontiers in Psychology (2023). DOI: 10.3389/fpsyg.2023.1175703

Thursday, February 22, 2024

How Robots Will Learn to Smell

Parenting a 3-year-old robot
Aug 2023,

RoboAgent, an artificial intelligence agent that leverages passive observations and active learning to enable a robot to acquire manipulation abilities on par with a toddler. The team's agent learns through a combination of self-experiences and passive observations contained in internet data. As a parent would guide their child, researchers teleoperated the robot through tasks to provide it with useful self-experiences.

Our novel policy architecture allows our agents to reason even with limited experiences, using temporal chunks of movements instead of commonly used per-timestep actions, and learning from videos on the internet, akin to how babies acquire knowledge and behaviors by passively observing their surroundings.

via Carnegie Mellon University and Facebook: RoboAgent and RoboSet Project - Towards Sample Efficient Robot Manipulation with Semantic Augmentations and Action Chunking. Homanga Bharadhwaj et. al. 

Post Script: Partnership between Carnegie Mellon University and Meta, which is exactly how you wanted this to happen.

Thursday, February 15, 2024

Calling All Chemosignals

Chemical communication between female rats exists and is complex
Jun 2023,

I'm just here because today I learned that mice urine and rat urine are very different:

At this point, MUP (major urinary proteins) enter into play. MUPs are key in the transmission of odors through marks, yet function differently in mice (found in the urine with which they mark) as opposed to rats (whose marks contains sebaceous secretions, in addition to urine).

But the research found that a variety of these scent marking proteins came from the clitoral glands of the females, and we didn't know that before. ... the combination of urine and the secretion from the clitoral glands is necessary for the marks of the females to arouse interest in other females.

via University of Córdoba, University of Liverpool: Guadalupe Gómez-Baena et al, Unraveling female communication through scent marks in the Norway rat, Proceedings of the National Academy of Sciences (2023). DOI: 10.1073/pnas.2300794120

Post Script: Scent marking in rats has been studied in depth when it comes to males, but, in the case of females,  there's a knowledge gap.

Hand odor can reveal a person's sex, study shows
Jul 2023,

Statistical analysis and mass spectrometry analyze the volatile scent compounds present on the palms of 60 individuals - half male and half female predicted a person's sex with a 96.67% accuracy rate.
via Florida International University: Multivariate regression modelling for gender prediction using volatile organic compounds from hand odor profiles via HS-SPME-GC-MS, PLoS ONE (2023). DOI: 10.1371/journal.pone.0286452

Post Script: On Handshakes and Animal Behavior, 2021

Thursday, February 8, 2024

Flood the Dataspace

A new approach to warding off mice eating wheat seed using camouflage scents
May 2023,

Spraying wheat fields with wheat germ oil after seeding deters mice that feed on seeds.

Mice consume approximately 70 million tons of maize, rice and wheat grains each year around the globe

Colleagues in New Zealand had tried smearing the scents of endangered birds over areas where the birds would never visit. This led to predators growing suspicious of such scents, because when followed, there was no payoff. That led them to ignore the smell of the birds even when they were present.

To see if the approach might work with mice, the team treated 60 10x10 plots with wheat germ oil, which contains the scent of the wheat germ - the part of the wheat the mice want to eat. To gauge its effectiveness, the team sprayed it on plots before planting seeds and others after seeding. They also left a few plots untreated.

They were surprised to find that the oil did not serve as a false signal; the mice still ate the seeds where the plots had been pretreated. But they also found that the mice largely left alone the plots where treatment had occurred after planting. This, the researchers suggest, was likely because an overabundance of aroma had confused the mice, making it nearly impossible for them to find the seeds.

via University of Sydney: Finn C. G. Parker et al, Olfactory misinformation reduces wheat seed loss caused by rodent pests, Nature Sustainability (2023). DOI: 10.1038/s41893-023-01127-3

Post Script: In the modern world where we scavenge for data more than we do food, and in an effort to protect our own personal data, quite valuable in this modern world, we would call this "data poisoning," where you might use a different name every time you register for a webservice or purchase an e-ticket, filling the spreadsheet with similar but not the same names, confusing the predictive analytics machine with dirty data. On this note, one bonus we can expect from the deluge of artificially-generated digital detritus coming our way, is that it will fill the entire internet with fake people, which will fill the entire data-bundle of your favorite data broker with fake people, all with fake addresses and fake phone numbers and fake preferences for consumer products, and this will collapse the surveillance advertising industry.  

Thursday, February 1, 2024

Interpersonal Olfactory Intelligence

One of the few people who really understands the intersection of language and smell, and what they mean for the truly scientific pursuit of knowledge in a field of study that refuses to submit to objective observation --

Meditations on Scent With Andreas Keller, the Socrates of Smell
Mar 2023, High Snobiety

"It’s very difficult to find a middle ground in talking about smell that conveys what's interesting and fascinating to you in a way that other people can understand,” Keller notes. “The limited vocabulary, the differences in perception between people, the emotional connection to smells… One way is to describe what a smell does to you, how it makes you feel – but that probably tells us more about yourself than about the smell.”

Unrelated image credit: This is not a picture of Andreas Keller, and it's not even a real person, because it's artificially generated. It's a "Rave Party for Jesus Birthday." Also pay artists for their work. 

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.