To detect aroma, airborne chemicals must enter into our nasal passages. Volatile aromatic oils carried in when we breathe, interact with receptors located along those passages.
Though flavor is somewhat influenced by our sense of smell, flavor primarily requires substance solubility in order to reach the different kinds of receptors located in various parts of the tongue. Let’s explore a little lemon chemistry.
Lemon Chemistry: Flavor
The tongue detects four, perhaps five, flavors. They are sweet, salty, sour, and bitter. Some add savory¹. There can be no doubt the primary taste of lemon is sour. Mention sour and the organic chemist thinks of organic acids. Lemons are rich in three organic acids: citric, malic, and ascorbic (AKA Vitamin C). Citric acid predominates. Suck on of citric acid and you’ll think of lemons.
Lemon Chemistry: Aroma
The odor of a lemon is a more complex matter. Much of its smell is located in the peel or zest. For this reason, zest is commonly used in gourmet cooking. But lemon peels are also of historical importance to furniture aficionados.
Many are familiar with lemon oil in furniture treatment compositions. Aromatic oil from the lemon includes and terpenes such as L-limonene². D-limonene, the stereoisomer of L-limonene distinguishes the aroma of oranges. Additional fragrant compounds include certain coumarins.
Unfortunately, today much “lemon oil” is not really lemon oil. It often is, as the Smithsonian Institution suggests, “mineral oil with colorants and perfumes added.”
Did You Know?
What exactly are terpenes? They are a class of organic compounds or structures that can be built from the building block, isoprene². The reader may note the similarity between the words isoprene and neoprene. Chlorinated isoprene or chloroprene was used to produce artificial rubber or neoprene during WW2. In fact, some researchers, even today, seek a commercially feasible process for reclaiming limonene by vacuum pyrolysis of used tires.
As is suggested above, the lemon aroma ingredient limonene is of great importance. It not only imparts the fragrance of the lemon in cooking and deodorants, it is useful in the treatment of furniture. It is also a highly valued “natural” cleansing agent to replace more toxic cleansers in general purpose use. Practical results from showing an interest in lemon chemistry suggests we avidly pursue the chemistry of every living thing in the ecosystem.
¹ Or, umami.
² For further information concerning terpenes and the isoprene rule, see Terpenes and Terpenoids: Isoprene Rule
- The Chemistry of a Lemon
- ACS: Volatile Components of Peel and Leaf Oils…
- Smithsonian Institute: Smell the Difference
- Harvard University: The Bittersweet Truth of Sweet and Bitter Taste Receptors
- Journal of the American Chemical Society: Chemical Composition of Lemon Oil…
- Materials Recycling World: Journal of Analytical and Applied Pyrolysis