UV-C Light Converts Chlorophyll to Pheophytin (Color Changes)
Ultraviolet light, especially UV-C (100–280 nm), can rapidly break down chlorophyll in cannabis ethanol extracts. The high-energy UV photons cause demetallation of chlorophyll – essentially knocking out the central magnesium ion to form pheophytin. This process, often called pheophytinization, turns the pigment from vibrant green to a dull olive-brown color. In food science, it’s well documented that heat or acid can similarly convert bright-green chlorophyll into pheophytin, yielding that drab olive hue (for example, in canned vegetables). UV-C light accelerates this transformation. Studies note that shorter UV wavelengths (<400 nm) have a stronger impact on chlorophyll degradation than longer wavelengths. In practical terms, exposing a chlorophyll-rich cannabis tincture to sunlight or UV-C will bleach out the green color, shifting the extract’s appearance from dark green to amber or brown as chlorophyll is destroyed. Researchers have observed that UV exposure of chlorophyll solutions produces not only pheophytin but also other breakdown products like chlorophyllide and pheophorbide. These changes are responsible for the fading of the green tint. In one experiment, UV light caused a 69% reduction in total chlorophyll content of an ethanolic plant extract after 60 minutes. With UV-C (higher energy) the bleaching can be even more complete – Scheepers et al. (2011) reported that UV irradiation could fully degrade chlorophyll a in plant extracts, leaving a nearly colorless (bleached) solution. Essentially, UV-C acts to de-green the extract by converting chlorophyll to its brownish derivatives, thereby lightening the final extract color.
On a molecular level, UV light excites chlorophyll and triggers electron transfer reactions that make the molecule unstable. This leads to the generation of reactive species like singlet oxygen and hydroxyl radicals. Those reactive oxygen species attack the chlorophyll structure, breaking it down into pheophytin and other fragments. Pheophytin itself is more photo-stable than chlorophyll (having no magnesium) but can still undergo further light-induced oxidation over time. The immediate visual effect of chlorophyll’s conversion to pheophytin is the loss of the bright green hue, often turning the extract to a pale brown or golden color if most chlorophyll is degraded. In summary, UV-C exposure plays a significant role in degrading chlorophyll to pheophytin, dramatically changing the extract’s appearance from green to brownish. This “sunlight bleaching” is sometimes used intentionally by extractors to improve oil color, though it must be balanced with the risk of also degrading cannabinoids (since UV light can affect those as well).
Solubility of Pheophytin in Ethanol vs Cannabinoids and Terpenes
Pheophytin shares similar solubility characteristics with chlorophyll because it retains the bulky hydrophobic phytol tail. Both chlorophyll and pheophytin are insoluble in water but very soluble in organic solvents like ethanol. In ethanol-based cannabis extraction, this means chlorophyll (and once formed, pheophytin) dissolves into the alcohol alongside cannabinoids and terpenes. In fact, ethanol’s polarity is just right to pull a wide range of compounds – it readily extracts cannabinoids and terpenes (which are non-polar to moderately polar), and unfortunately it also efficiently extracts chlorophyll pigments. Chlorophyll’s strong ethanol solubility is why ethanol extracts often turn deep green. Pheophytin remains equally soluble in ethanol, so converting chlorophyll to pheophytin via UV doesn’t precipitate it out of solution; the pigment (now in pheophytin form) will still stay dissolved in the tincture. In other words, UV exposure changes the pigment’s chemistry but doesn’t make it any less present in the liquid extract – it simply changes its color and form.
Comparatively, cannabinoids like THC and CBD are also soluble in ethanol, though their solubility can depend on ethanol strength and temperature. Terpenes (aromatic oils) mix well with ethanol too, since ethanol can dissolve a fair amount of non-polar compounds despite being a polar solvent. All these constituents (cannabinoids, terpenes, chlorophyll/pheophytin) tend to co-dissolve in high-proof ethanol. If the goal is to remove pigments, some processors use techniques like cold ethanol extraction (at -20 °C or lower) to minimize chlorophyll pickup (Removing Chlorophyll From Alcohol Extracts – Media Bros). Cold ethanol is less efficient at dissolving chlorophyll, taking advantage of the reduced solubility of pigments at low temperatures, while still extracting cannabinoids. But once chlorophyll or pheophytin is in the ethanol solution, it won’t separate on its own. It can, however, be pulled out by other means – for example, an oil partition method showed that when an ethanol extract is diluted with some water (making it 25–75% ethanol) and mixed with vegetable oil, over 85% of chlorophyll can move into the oil layer. This works because adding water makes the chlorophyll/pheophytin less happy in the now more polar ethanol phase, driving it into the non-polar oil phase. In summary, pheophytin dissolves about as readily in ethanol as chlorophyll does, and just like cannabinoids and terpenes, it will remain in an ethanol extract unless deliberately removed. The key difference is that cannabinoids and terpenes are desired components, whereas chlorophyll/pheophytin are often considered contaminants imparting unwanted color.
Effects on Taste and Harshness of the Final Product
Chlorophyll in cannabis extracts is notorious for affecting flavor and smoothness. It imparts a “green,” grassy or bitter taste that many users find undesirable (To Green or Not to Green: Navigating Chlorophyll in RSO and Cannabis Extracts – Hillsborough, NJ, Flemington, NJ & Somerville, NJ | Valley Wellness). This is analogous to the bitter notes you get from eating raw leafy greens – chlorophyll has a distinctly bitter profile. In concentrates like Rick Simpson Oil (RSO) or ethanol tinctures, a high chlorophyll content can make the product taste harsh, earthy, or even “vitriolic” (as one source describes it) (To Green or Not to Green: Navigating Chlorophyll in RSO and Cannabis Extracts – Hillsborough, NJ, Flemington, NJ & Somerville, NJ | Valley Wellness). It can also contribute to a throat irritation or roughness when smoking or vaping, because plant pigments don’t vaporize cleanly and can leave a burnt aftertaste.
Degrading chlorophyll to pheophytin via UV exposure can somewhat mitigate the intensity of these effects, but it doesn’t entirely eliminate them. Pheophytin is chemically similar to chlorophyll (just minus the magnesium), so it likely shares some of the organoleptic properties. There is limited research on the taste of pheophytin specifically, but since it remains a large polycyclic organic molecule, it may still taste bitter or cause slight harshness if present in quantity. The main improvement from chlorophyll breakdown is that the “fresh plant” grassy flavor diminishes as the vibrant chlorophyll is destroyed. Anecdotally, many extractors report a smoother taste after sun-bleaching a tincture, noting that the extract’s flavor becomes less like “raw cannabis juice.” Indeed, the cannabis industry often takes steps to remove or reduce chlorophyll for this very reason: removing the chlorophyll yields an oil with a cleaner taste and aroma. For instance, edible oil producers use activated clays to strip out chlorophyll from canola oil specifically to eliminate its bitter taste – highlighting that chlorophyll is recognized as a bitterness contributor in foods.
It’s important to note that simply converting chlorophyll to pheophytin by UV might not improve taste as much as physically removing the pigments. The breakdown products (pheophytins, chlorophyllides, etc.) are still present as “impurities” in the final product. If they remain, they can continue to contribute off-flavors (perhaps a duller, more hay-like bitterness instead of a bright green bitterness). Complete removal (through filtration, adsorption, or partitioning) tends to have the greatest benefit for taste. Nonetheless, sunlight/UV treatment does reduce the chlorophyll content, which can make the extract slightly less bitter and harsh. Many processors report the extract’s taste becomes more palatable (and the color more visually appealing) after UV exposure – hence the practice of sun-bleaching an ethanol tincture to improve its organoleptic qualities. Just keep in mind that excessive UV can degrade other desirable components too, so there’s a balance to be struck.
Quantitative Studies on UV-C Chlorophyll Breakdown in Ethanol
Several scientific studies have quantified how light (including UV-C) breaks down chlorophyll in solution:
- Scheepers et al. (2011) – This study used UV irradiation to bleach plant extracts for better analytical testing. They reported that chlorophyll a was successfully degraded by UV in all samples, leaving a clear (nearly colorless) extract. This implies essentially 100% conversion of chlorophyll to its degradation products under their UV treatment. (While the paper doesn’t explicitly state the wavelength, the context suggests a shortwave UV lamp likely including UV-C was used to achieve complete bleaching.) The goal was to eliminate chlorophyll interference, and HPLC analysis confirmed the pigment’s disappearance after UV exposure.
- Yasuda et al. (2019) – In a Food Chemistry study, researchers examined chlorophyll discoloration rates in mixed methanol/ethanol solutions under UV light. They found the rate depended on chlorophyll’s physical state (monomer vs aggregated). Notably, they observed that in high ethanol concentrations (≥60%), chlorophyll a solutions rapidly changed from green to pale brown under light. Monomeric chlorophyll bleached much faster than aggregated chlorophyll. Though this study focused on UV-A light, it demonstrated quantitatively that about 69% of total chlorophyll content could be destroyed in 60 minutes under intense UV-A exposure. UV-C, being higher energy, would likely cause equal or greater breakdown in a similar or shorter time. The authors proposed a mechanism where light-induced electron transfer in chlorophyll produces reactive oxygen that attacks the pigment, leading to formation of pheophytin and other derivatives.
- Verduin et al. (2020) – This review on photodegradation of food pigments notes that wavelengths below 400 nm (UV range) accelerate chlorophyll breakdown via photo-oxidation. They cite that light exposure causes loss of Mg (forming pheophytin) and further oxidation of chlorophyll derivatives. For example, in olive oil exposed to light, both chlorophyll a and b steadily decreased while pheophytin (their demetallized form) appeared, until even the pheophytin began to photo-oxidize. These findings underline that UV (especially UV-B/UV-C) quickly triggers chlorophyll degradation in organic solutions. Quantitatively, the extent of degradation correlates with UV dose: one report mentioned a 12% drop in total chlorophyll in a plant extract after a low UV-C dose, and greater losses with higher doses.
- Lante et al. (2023) – Although dealing with UV-A, this study on phenolic extracts is relevant. It showed that strong UV-A LED treatment could deplete chlorophyll a by nearly 90% (from ~256 μg/g down to ~29 μg/g in one sample). It also confirmed the generation of chlorophyll breakdown products like pheophytins during irradiation. This gives a sense of the magnitude of chlorophyll loss under controlled UV exposure. We can infer that UV-C would be at least as effective, if not more, given its higher energy; indeed, UV-C is commonly used in laboratory bleaching of chlorophyll as noted above.
In summary, quantitative data from these studies demonstrate significant chlorophyll breakdown under UV light. UV-C in particular can swiftly convert a majority of chlorophyll to pheophytin and other derivatives, substantially reducing the chlorophyll content in ethanol solutions. The result is a bleached, lighter-colored extract. These findings back the anecdotal practice of using sunlight or UV lamps to clarify green cannabis extracts – though one should apply this carefully. The data-driven evidence confirms that UV exposure (including UV-C) is an effective tool for chlorophyll degradation: for instance, complete bleaching was achieved in a lab setting, and ~70% degradation in an hour with milder UV was reported in another case. This gives extractors a ballpark of what to expect if they intentionally use UV-C: a pronounced loss of chlorophyll in relatively short time frames.
References:
- Verduin et al., Food Sci. & Nutr. (2020) – Photodegradation of chlorophyll and formation of pheophytin.
- Lante et al., J. Sci. Food Agric. (2023) – UV-A light degrades ~69% of chlorophyll in ethanol extracts in 60 min.
- Scheepers et al., Afr. J. Biotechnol. (2011) – UV (including UV-C) completely bleaches chlorophyll in plant extracts.
- Media Bros (Cannabis Science Tech, 2021) – Ethanol co-extracts chlorophyll (green color, bitter taste).
- Valley Wellness NJ (2023) – Chlorophyll in extracts causes grassy, harsh taste (To Green or Not to Green: Navigating Chlorophyll in RSO and Cannabis Extracts – Hillsborough, NJ, Flemington, NJ & Somerville, NJ | Valley Wellness).
- Sigma-Aldrich/Food Chemistry data – Chlorophyll a & pheophytin a are insoluble in water but soluble in ethanol and organic solvents.
- Phaisan et al. (2020) – Oil partition method removes >85% chlorophyll from ethanolic extract when water is added.
- Yasuda et al., Food Chem. (2019) – Mechanism of chlorophyll discoloration under UV, aggregates vs monomers.
- iGEM Canola Oil Study (2019) – Removing chlorophyll to avoid bitter taste in oils.
