(Alt text – A cotton candy vendor walking under the forest canopy during a morning in Bardiya National Park in Nepal, light filtering through the canopy. By Gaurav Aryal, Shutterstock.com)
Like everyone else, the start of the new school year has been incredibly stressful for me. Going for walks in the arboretum on campus has been a huge coping mechanism, especially on the days when I just want to go home and curl up in a ball with the blankets over my head.
The arboretum is a spectacular sight this time of year, with maples, birches, and beeches showing off in russets, scarlets, and golds. But there’s a quiet little grove in the middle of this amazing space that also has a treat for your nose: if you’re standing in the right spot and inhale deeply, be ready for caramel, fresh-out-of-the-oven cake cooling on the counter, or, in my opinion, cotton candy. The source of this incredible scent is the katsara tree (Cercidiphyllum japonicum), a tree native to Japan and China that was imported to North America in the mid-1800s.
As the heart-shaped leaves begin to turn from green to yellow to brown every autumn, an aromatic molecule called maltol is released to the air, in concentrations high enough that it can smell like walking past the waffle station at your favourite brunch spot. The scent is so strong and so distinctive that katsuras are known as “kuchenbaum” (cake tree) in German or “arbre à caramel” (caramel tree) in French.
Maltol, chemical formula C6H6O3, occurs naturally in certain foods like coffee and cocoa, getting converted from sugars to this amazing smelling molecule in the baking or roasting process. Maltol is also found in pine needles, the bark of larch trees, and red ginseng. The white crystalline powder with the butterscotch fragrance is extensively used in the food industry as a flavouring agent as well as an additive in perfumes.
When I first noticed the smell a few years ago, I was honestly completely baffled. It was always in the same spot but it wasn’t always noticeable. Some days it would be incredibly strong but then months would go by without the slightest whiff. Looking around for the source of the scent, there are no flowers (or bakeries) in sight. But, with the help of the arboretum signage and Google, the mystery was revealed. And I was greatly relieved to find out that I wasn’t having some kind of stress-induced olfactory hallucination!
The map of the arboretum – the katsura collection is #6 here 
The legend from the arboretum map 
The sign at the foot of the katsura tree that helped me to figure out the source of this amazing smell 
The path through the katsura grove in the Arboretum at the University of Guelph. Trees on either side of a dirt path, a light dusting of yellow/brown leaves on the ground.
With a little digging, I found myself reading about some pretty incredible properties of this deliciously scented molecule. Researchers are exploring its antioxidant capabilities and its potential application in treating a huge array of concerns, from liver disease to osteoarthritis, glaucoma to bacterial resistance to common antibiotics. Among other functions, maltol works to control the amount of metal in the human body, forming stable complexes with metallic ions like Al+3, Fe+3, Zn+2, etc. Some of these complexes have been investigated as possible treatments for anemia, Alzheimer’s, cancer, and diabetes. So it turns out that my favourite spot to destress in the arboretum is full of amazing science, right under my nose.
References
Maltol, a Food Flavoring Agent, Attenuates Acute Alcohol-Induced Oxidative Damage in Mice. Ye Han, Qi Xu, Jiang-ning Hu, Xin-yue Han, Wei Li and Li-chun Zhao Nutrients 2015, 7(1), 682-696
Novel Synthesis of Maltol Capped Copper Nanoparticles and Their Synergistic Antibacterial Activity with Antibiotics. Naqvi et al 2021 Plasmonics https://doi.org/10.1007/s11468-021-01452-3
Maltol prevents the progression of osteoarthritis by targeting PL3K/Akt/NF-kB pathway: in vitro and in vivo studies. Lu et al 2021 J Cell Mol Med25: 499-509 https://doi.org/10.111/jcmm.16104
