Celery, with its crisp texture and refreshing taste, is more than just a salad ingredient. Its unique aroma and flavor have made it a subject of scientific curiosity, especially in understanding how environmental factors shape its chemical profile.
A groundbreaking study published in Food Chemistry: X (2025) reveals that ultraviolet (UV) radiation significantly alters the flavor of celery by boosting the production of aroma compounds.
Led by researchers at Qingdao Agricultural University, this study identifies over 1,600 volatile molecules in celery and explains how controlled UV exposure can enhance its taste for culinary, cosmetic, and industrial uses. Let’s explore how light transforms this humble vegetable.
Understanding Celery’s Flavor Chemistry
The flavor of celery comes from tiny molecules called volatile organic compounds (VOCs). These are chemicals that easily evaporate at room temperature, releasing scents that interact with our sense of smell.
VOCs are not unique to celery—they are produced by many plants as part of their natural defense mechanisms, helping attract pollinators, repel pests, or respond to environmental stress. In celery, the most important VOCs fall into three main categories:
- Terpenes: These are the largest group of plant-derived chemicals, known for their woody, citrusy, or floral aromas. Examples include limonene (citrus scent) and germacrene D (woody spice). Terpenes are also found in essential oils like lavender and eucalyptus.
- Esters: These compounds create fruity or sweet smells. For instance, 3-mercapto-3-methylbutyl formate, an ester in celery, has a tropical, caramel-like aroma.
- Heterocyclic Compounds: These molecules contain rings made of different atoms (like nitrogen or sulfur) and often smell nutty, roasted, or earthy. A key example is 2-methoxy-3,5-dimethylpyrazine, which gives celery a bread-like undertone.
Interestingly, different parts of the celery plant—leaves and stalks (petioles)—produce distinct flavors. Leaves are often rich in earthy, herbal tones, while stalks tend to be milder and greener.
To study how UV light affects these compounds, researchers grew celery in a controlled environment using artificial lighting. One group of plants received standard white and red LED light, while another group was exposed to the same lights plus supplemental UV-A radiation.
After 30 days, the team analyzed the leaves and stalks using advanced tools like gas chromatography-mass spectrometry (GC-MS), a technique that separates and identifies chemicals based on their molecular weight and structure.
Key Findings: UV Radiation Boosts Flavor Complexity
The results were striking. Celery exposed to UV light produced a wider variety of aroma compounds compared to untreated plants. Across both leaves and stalks, researchers detected 1,640 distinct VOCs, grouped into 15 classes. Terpenes, known for their woody and citrusy scents, made up 20% of all compounds.
Esters, which add fruity sweetness, accounted for 18%, while heterocyclic compounds contributed 11% with their nutty and roasted notes.
UV treatment caused significant changes in these compounds. For example, leaves exposed to UV light showed higher levels of trans-β-ionone, a molecule with a dry, floral aroma.
Its relative odor activity value (rOAV)—a measure of how much a compound contributes to overall scent based on its concentration and human detection threshold—jumped from 22,384 in untreated leaves to 14,054 in UV-treated ones.
Similarly, stalks under UV light saw a surge in (E,Z)-2,6-nonadienal, a compound with a fresh cucumber-like scent, which reached an rOAV of 2.3 million compared to 1.48 million in control samples.
Another notable change occurred in limonene, a terpene responsible for citrusy zing. UV-treated stalks had limonene levels nearly double those of untreated ones (rOAV of 10,944 vs. 5,296). These shifts highlight how UV radiation can amplify specific flavors, making celery more aromatic and complex.
Why UV Light Makes a Difference
Plants respond to UV light as a form of mild stress. When exposed, they activate defense mechanisms that include producing protective chemicals. In celery, UV radiation triggered two key biochemical pathways:
The Methylerythritol Phosphate (MEP) Pathway: This is a series of chemical reactions in plant cells that produce terpenes, the building blocks of many essential oils. UV light boosted the activity of genes in this pathway, leading to higher terpene levels.
The Phenylpropanoid Pathway: This process creates phenolic compounds, which contribute to floral and spicy aromas. UV exposure increased the activity of an enzyme called phenylalanine ammonia-lyase (PAL), which kickstarts this pathway.
Interestingly, stalks reacted more strongly to UV than leaves. This might be because stalks, which are typically shielded from direct sunlight in nature, are more sensitive to artificial UV exposure.
The study also found that UV treatment increased the activity of genes linked to terpene synthesis, leading to higher levels of compounds like germacrene D (woody and spicy) and limonene.
Practical Implications for Farmers and Food Producers
For farmers, these findings offer a way to grow celery with customized flavors.
- By adjusting UV exposure, they could emphasize specific traits—citrusy stalks for salads, woody leaves for soups, or floral notes for herbal teas.
- This approach could also reduce waste, as enhancing the flavor of often-discarded stalks might make them more appealing to consumers.
- The food industry could benefit too. UV-treated celery extracts might replace artificial flavorings in snacks, sauces, and beverages, aligning with the demand for natural ingredients.
- Additionally, terpenes like limonene and germacrene D have antioxidant properties, suggesting that UV-enhanced celery could offer added health benefits, such as reducing inflammation or combating harmful microbes.
Challenges and Considerations
Despite its promise, UV treatment has limitations. Setting up UV lighting systems in greenhouses or plant factories can be costly, with initial investments reaching thousands of dollars.
Overexposure to UV can also damage plants, requiring careful monitoring of light intensity and duration. The study used a specific celery variety (Daychuang), so results might differ for purple or Chinese celery.
Consumer preferences are another factor. While some might enjoy stronger flavors, others could find them overwhelming. Future studies could explore balancing aroma intensity or combining UV with other light wavelengths, like blue or far-red, to fine-tune results.
The Future of Flavor Science
This research opens doors to broader applications. For instance, could UV treatment improve the flavor of other herbs like parsley or cilantro? Might post-harvest UV exposure extend the shelf life of fresh produce?
The study’s methods—combining metabolomics (the study of small molecules in organisms) with advanced light control—provide a model for answering these questions.
As climate change alters growing conditions, such precision agriculture techniques will be vital. Farmers could use UV light to maintain crop quality even in suboptimal environments, ensuring consistent flavor and nutrition.
Conclusion
The relationship between light and flavor is more profound than we once thought. This study shows that UV radiation isn’t just a tool for growth—it’s a lever to pull for enhancing taste, aroma, and even health benefits. For scientists, it’s a call to explore how other wavelengths or stressors could shape food chemistry.
For consumers, it’s a reminder that the future of food lies not just in what we grow, but in how we grow it. By harnessing the power of light, we can turn everyday vegetables like celery into extraordinary ingredients, bridging the gap between nature’s potential and human ingenuity.
Power Terms
Volatile Organic Compounds (VOCs):
VOCs are chemicals that evaporate easily at room temperature, releasing distinct smells. They are crucial in plants for attracting pollinators, repelling pests, and contributing to flavor. In celery, VOCs like terpenes and esters determine its aroma. For example, the study found 328 terpenes and 299 esters in celery.
Terpenes:
Terpenes are a large class of organic compounds produced by plants, often responsible for floral, citrus, or woody scents. They are key contributors to celery’s aroma and are synthesized through metabolic pathways like the methylerythritol phosphate pathway. Examples include limonene (citrus scent) and germacrene D (woody aroma).
Esters:
Esters are organic compounds formed from acids and alcohols, often associated with fruity or sweet smells. In celery, esters like 3-methylbutyl formate contribute to its flavor. The study noted that UV radiation altered ester levels in celery leaves.
Heterocyclic Compounds:
These are organic compounds containing rings made of carbon and other atoms (like nitrogen or oxygen). In celery, pyrazines (a type of heterocyclic compound) create earthy or nutty aromas. For example, 2-methoxy-3,5-dimethylpyrazine adds a bread-like odor.
Ketones:
Ketones are organic compounds with a carbonyl group. They often contribute sweet or fruity notes. In celery, ketones like 5-ethyl-3-hydroxy-4-methyl-2(5H)-furanone enhance caramel-like flavors.
Gas Chromatography-Mass Spectrometry (GC-MS):
A laboratory method used to separate and identify chemical compounds in a sample. The study used GC-MS to analyze celery’s VOCs by vaporizing compounds (gas chromatography) and breaking them into fragments (mass spectrometry) for identification.
Headspace Solid Phase Microextraction (HS-SPME):
A technique to collect VOCs from a sample without direct contact. In the study, celery parts were sealed in vials, and a fiber absorbed volatile compounds from the “headspace” (air above the sample) for GC-MS analysis.
Principal Component Analysis (PCA):
A statistical tool to simplify complex data by highlighting patterns. The study used PCA to group celery samples based on VOC similarities, showing clear differences between UV-treated and untreated plants.
Orthogonal Projections to Latent Structures-Discriminant Analysis (OPLS-DA):
A method to identify differences between groups in datasets. The researchers used OPLS-DA to pinpoint which VOCs changed significantly in UV-exposed celery.
Variable Importance in Projection (VIP):
A score indicating how much a compound influences group differences in statistical models. Compounds with VIP >1 were considered significant in the study, such as terpenes altered by UV radiation.
Relative Odor Activity Value (rOAV):
A measure of a compound’s contribution to aroma, calculated as rOAV = Concentration (Ci) / Odor Threshold (Ti). For example, 2,6-nonadienal had a high rOAV, meaning its cucumber-like scent strongly impacted celery’s flavor.
Kyoto Encyclopedia of Genes and Genomes (KEGG):
A database for biological pathways. The study used KEGG to link celery’s VOCs to metabolic processes, like terpenoid biosynthesis.
Sesquiterpenes:
A subclass of terpenes with 15 carbon atoms, often contributing woody or spicy notes. Germacrene D, a sesquiterpene in celery, was upregulated by UV radiation.
Triterpenes:
Larger terpenes with 30 carbons, involved in plant defense. The study found UV radiation influenced triterpene biosynthesis pathways in celery.
Phenylpropanoid Biosynthesis:
A metabolic pathway producing compounds like lignin and flavonoids. In celery, UV radiation increased phenylpropanoids, which may enhance antioxidant capacity.
Metabolomics:
The study of small molecules (metabolites) in organisms. The paper used metabolomics to profile how UV radiation altered celery’s flavor-related compounds.
Ultraviolet Radiation (UV):
Invisible light with wavelengths shorter than visible light. The study tested UV-A (315–400 nm) and UV-B (280–315 nm); UV-C (100–280 nm) doesn’t reach Earth. UV exposure boosted celery’s VOCs.
UV-A:
Long-wave UV light (315–400 nm) that penetrates deeper into plants. The study applied UV-A to celery, increasing terpenes and esters.
UV-B:
Mid-range UV (280–315 nm) that can stress plants but also trigger protective compounds. Though not directly used here, UV-B is known to affect plant metabolites.
UV-C:
Short-wave UV (100–280 nm), mostly blocked by Earth’s ozone. It’s not relevant to natural sunlight but is used in labs for sterilization.
Plant Factory with Artificial Lighting (PFAL):
Indoor farms using controlled light, temperature, and humidity. The study grew celery in PFALs to standardize UV exposure conditions.
Secondary Metabolites:
Compounds plants produce for defense or signaling (not growth). Examples in celery include terpenes and phenolics, which UV radiation increased.
Flavor Precursors:
Non-volatile compounds that transform into aroma-active molecules. For example, sugars in UV-exposed celery may break down into fruity esters during processing.
Volatile Metabolomics:
A subset of metabolomics focusing on volatile compounds. The study used this to map how UV altered celery’s aroma profile.
Odor Threshold:
The minimum concentration at which a compound becomes detectable by smell. For instance, 2-methoxy-3,5-dimethylpyrazine has an odor threshold of 0.0000004 ppm, making it impactful even in tiny amounts.
Reference:
Yan, Z., Li, Z., Wang, H., Dou, H., Song, J., Ji, F., Yang, Y., & Lin, D. (2025). Volatile metabolomics analysis reveals the flavor response of different parts of celery to ultraviolet radiation. Food Chemistry: X, 25, 102213. https://doi.org/10.1016/j.fochx.2025.102213
