Chlorophyll is the green pigment in plants that allows them to capture light energy, making it the bedrock of nearly all life on Earth. This molecule is widely known for giving leaves and grass their vibrant color and for driving photosynthesis. The fresh aroma of nature is often attributed directly to the chlorophyll molecule itself, but this is a misunderstanding. Understanding what causes this specific scent requires separating the pigment’s biological function from the complex chemistry of plant defense mechanisms.
Describing the Scent
The aroma commonly described as the smell of chlorophyll is fresh, earthy, and distinctly “green.” This sensory experience is most noticeable after activities like mowing a lawn, crushing herbs, or juicing leafy vegetables. The smell is often characterized by a clean, vibrant burst, making it a universally recognized and generally pleasant scent. It carries a wet, herbaceous quality, often likened to freshly cut stems or the air after a summer rain, signaling a high concentration of ruptured plant material.
The Chemical Cause of the Smell
The vibrant aroma of “green” is not produced by the chlorophyll molecule itself, which is largely odorless. Instead, the smell originates from a family of volatile organic compounds (VOCs) that are instantaneously released when a plant’s cell walls are ruptured. These compounds are collectively known as Green Leaf Volatiles (GLVs), and their rapid production is a biochemical response to tissue damage. Specific GLVs responsible for the characteristic grassy smell include C6-aldehydes and C6-alcohols, such as (2E)-hexenal (“leaf aldehyde”) and (3Z)-hexenol (“leaf alcohol”).
The biosynthetic pathway for these compounds begins with unsaturated fatty acids stored in the plant membranes. When the cell is injured, a series of enzymes, notably lipoxygenase and hydroperoxide lyase, rapidly convert these fatty acids into the volatile C6 compounds. For instance, the enzyme hydroperoxide lyase cleaves a fatty acid hydroperoxide to generate the sharp-smelling aldehydes. These volatile molecules serve an ecological function for the plant, acting as a defense mechanism to deter herbivores and as airborne wound signals to neighboring plants.
Scent Differences in Supplements and Raw Plants
The scent of raw, freshly processed plant juice differs significantly from the aroma of commercial liquid chlorophyll supplements. When chlorophyll is extracted for supplements, it undergoes a chemical process to create a semi-synthetic derivative called chlorophyllin. This process replaces the magnesium atom at the center of the natural chlorophyll molecule with a copper ion, which increases the compound’s stability and makes it highly water-soluble.
Because this derivative is chemically altered, the resulting product loses the volatile C6 compounds responsible for the fresh, grassy smell of raw plants. The copper-containing chlorophyllin has a much milder and less herbaceous odor, often described with metallic, alkaline, or medicinal notes. Chlorophyllin is frequently used as an internal deodorizer, chemically neutralizing other odor-causing compounds. Many commercial liquid supplements also contain flavorings like mint to mask any remaining natural or metallic flavor.
Role of Chlorophyll in Plant Life
The function of chlorophyll is to capture light energy and initiate photosynthesis. Chlorophyll molecules are located within the chloroplasts of plant cells, where they absorb light most effectively in the red and blue portions of the spectrum. Since green light wavelengths are largely reflected, the pigment and the leaves containing it appear green to the human eye. The absorbed energy is transferred to generate chemical energy. The overall process converts atmospheric carbon dioxide and water into glucose, a sugar the plant uses for fuel, while releasing oxygen as a byproduct.