This series of posts will highlight the plants that help you celebrate the Yuletide season.
From candy canes to lattes, peppermint just tastes like winter. Here’s more on the flora behind the flavor.
Peppermint is a sterile hybrid (Mentha × piperita) of watermint (Mentha aquatic) and spearmint (Mentha spicata). Even though it doesn’t produce seeds, it is a prolific propagator via vegetative growth of stolons (plant biology word of the day). In the case of mint, stolons are runners of the root system just below the soil surface that can establish their own root system and plant. Because mint is very good at this, it can be quite invasive once it gets established. For your home herb garden, I would suggest growing it in a container to keep it corralled. For commercial production, certified disease-free rootstocks are used and continue producing good yields of high quality oil for about four years.
The Pacific Northwest wins for mint production because conditions in Washington, Oregon and Idaho are ideal for producing high quality oil. Oregon leads the U.S. in peppermint production, but Washington produces the most total mint oil (from both peppermint and spearmint). Candy canes and other seasonal candy represent a small sector of mint oil demand. The majority of mint oil (90%) is split equally for flavoring of chewing gum and dental products (toothpaste and mouthwash). Altogether, mint oil is big business worth approximately $200 million annually.
The distinct peppermint flavor is a mixture of chemicals that the plant makes and stashes in specialized structures called glandular hairs on its leaves. These volatile aromatic compounds are readily distilled into concentrated oils. We may associate the flavor with winter, but mint is harvested in the summer. The fields are mowed down, dried, then the plant material is steam-distilled to extract the oil. The main ingredient is menthol, but peppermint flavoring is a complex mixture of this ingredient with numerous other molecules. Chemists may have figured out synthetic menthol production, but oil distilled from peppermint plants is still the method of choice for flavoring production.
Because peppermint plants could care less about what our candy canes and lattes taste like, there are scientists dedicated to understanding the biochemical pathways behind the plant’s unique flavor so we can produce more of it. Mark Lange and Rodney Crouteau at the Institute of Biological Chemistry at Washington State University (Pullman) have been studying the production of natural plant products like terpenoids (bonus plant biology word of the day), which includes mint flavorings. These scientists have been working with growers and processors to increase mint oil yields and quality. Developing a biosynthetic map of the chemistry that plants use to make their aromatic compounds provided a framework for generating superior peppermint that produces more and better oil. The strategy involves transgenic technology to reduce the enzymes that would make less desirable chemical compounds and increase the enzymes that produce more desirable compounds. Because these are specialized plant chemicals, the genes are all from plants and mainly reconfigurations of the peppermint’s own DNA. Because peppermint plants are sterile, there is minimal risk of these transgenes escaping into neighboring non-transgenic plants. Also, because the commercial peppermint product, the essential oil, is a concentrated extraction of just the chemicals, there is virtually no chance any altered DNA or foreign proteins (GMO) enter the consumed products. Nevertheless, it is sometimes necessary to mark in some way transgenic-derived oils. For this purpose, an enzyme was introduced to produce (+)-limonene, a compound classified as ‘generally recognized as safe’, which can serve as a chemical marker for transgenic mint oil without affecting yield or quality. Because classical breeding techniques are not applicable to peppermint plants, these transgenic solutions offer a way to keep our domestic mint competitive in a global market.
Chewing gum, toothpaste and mouthwash have made mint flavoring an everyday occurrence, but there is a physiological reason that peppermint is the flavor of winter. It turns out that the cooling sensation of mint (think breath mints or menthol chest rubs) is not just a marketing gimmick. The main peppermint flavor ingredient, menthol, activates TRPM8 (aka Transient Receptor Potential cation channel subfamily M member 8), which is involved in neuronal signaling of cooling sensations. The action of TRPM8 (a channel that allows for the flux of cations like calcium) is part of the biochemical basis for how mammals sense temperature, innocuous cooling specifically. Because menthol triggers TRPM8 into action at warmer temperatures than it normally would, it makes us feel like we are cooler than we actually are.
So, chew on that for a while; that’s a lot of seasonal science to swallow.
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