The Dominant Bioactive Compound: Citral
At the heart of lemon myrtle's potent fragrance and therapeutic properties is its exceptionally high concentration of citral. This essential oil component is actually a blend of two isomeric aldehydes: neral (also known as citral b) and geranial (citral a). While many plants contain citral, lemon myrtle contains it in a significantly higher and purer concentration, often exceeding 90% in its essential oil. This impressive composition gives it a cleaner, sweeter, and more potent lemon aroma than many other citrus-scented plants, such as lemongrass or lemon verbena. The citral content is directly responsible for many of the herb's key biological effects, including its powerful antimicrobial and antifungal activity.
Minor Essential Oil Constituents
While citral is the star player, a range of minor and trace compounds contribute to lemon myrtle's complex character and full spectrum of benefits. These typically make up only a small percentage of the total oil composition but are significant in enhancing its properties.
- Myrcene: This monoterpene has a pleasant, earthy, and slightly musky aroma. It is also found in hops, lemongrass, and bay leaves and possesses anti-inflammatory properties.
- Linalool: A naturally occurring alcohol that imparts a floral, woody aroma. It is often associated with calming and relaxing effects, and some studies have shown it has antimicrobial properties as well.
- Citronellal: A less common chemotype of lemon myrtle produces oil high in citronellal, which acts as an effective insect repellent.
- Iso-citrals: These isomers of citral may appear in small amounts and are sometimes formed during distillation or oxidation.
- Methylheptenone: Another ketone present in small quantities that contributes to the overall aromatic profile.
The Rich Nutritional Profile: Vitamins and Minerals
Beyond its powerful essential oils, lemon myrtle is a nutritional powerhouse, especially when consumed as a tea or added to food. The leaves contain a broad spectrum of vitamins and minerals that support overall health.
- Vitamin C: A potent antioxidant crucial for immune function, tissue repair, and iron absorption. Lemon myrtle provides a significant amount of this vital vitamin.
- Vitamin E: Another important antioxidant that helps protect the body's cells from oxidative stress and damage caused by free radicals.
- Folate: An essential B-vitamin that plays a critical role in cell growth, metabolism, and DNA synthesis and repair.
- Calcium: A vegan-friendly source of this mineral, vital for strong bones, teeth, and muscle function.
- Magnesium: Essential for energy production, nerve function, and supporting a healthy heart rhythm.
- Potassium: Helps regulate blood pressure and supports healthy kidney and muscle function.
- Zinc: An important trace mineral for immune system support and wound healing.
- Lutein: A carotenoid antioxidant that is particularly beneficial for eye health, helping to prevent age-related macular degeneration.
Comparison: Lemon Myrtle vs. Lemon
While often compared due to its flavour profile, lemon myrtle and lemon differ significantly in their chemical makeup and properties. The following table illustrates some key differences.
| Feature | Lemon Myrtle | Lemon (Citrus limon) |
|---|---|---|
| Dominant Essential Oil | Citral (Neral + Geranial) | Limonene (primarily) |
| Citral Content | Exceptionally high (80-98%) | Very low (2-3%) |
| Flavour Profile | Intense, sweet, complex citrus with hints of verbena and eucalyptus | Brighter, more acidic, sometimes bitter citrus |
| Acidity | Non-acidic, making it versatile for dairy-based dishes | Highly acidic due to citric acid content |
| Antioxidant Levels | High levels, often higher than blueberries or tea | Contains antioxidants, but less concentrated than lemon myrtle |
| Preparation | Used dried, ground, or as essential oil; fresh leaves are not edible | Zest, juice, and segments are commonly used |
The Science Behind Lemon Myrtle's Bioactivities
Research has affirmed the potent bioactivities that Indigenous Australians have long recognised in this native plant. The synergistic effect of its compounds, especially the high citral content and other antioxidant polyphenols, is responsible for its powerful health-promoting effects.
- Antimicrobial Power: The high concentration of citral makes lemon myrtle a potent agent against bacteria, fungi, and viruses. Studies have shown its efficacy against a wide range of microorganisms, including Staphylococcus aureus and Candida albicans, often outperforming tea tree oil in comparative tests.
- Anti-inflammatory Effects: Polyphenols found in lemon myrtle have been shown to have anti-inflammatory properties, which can help soothe conditions like sore throats and digestive tract inflammation.
- Antioxidant Activity: The rich supply of antioxidants helps combat oxidative stress and protect against cellular damage caused by free radicals. This is linked to its potential to prevent chronic diseases.
Culinary vs. Medicinal Forms and Uses
The form of lemon myrtle dictates how its properties are best harnessed. Different preparations maximise different benefits, from flavour to therapeutic effects.
Culinary Uses
- Dried Leaves or Ground Spice: Excellent for flavouring dishes, desserts, teas, and drinks. Adds a refreshing citrus note without the acidity of lemons.
- Teas and Infusions: A soothing, caffeine-free beverage rich in antioxidants. Can aid digestion and promote relaxation.
Medicinal/Aromatherapy Uses
- Essential Oil: A highly concentrated form used for its powerful antimicrobial and aromatherapy benefits. The citral is potent, so it must be diluted for skin application.
- Topical Applications: When diluted with a carrier oil, it can be used on the skin to help with acne, insect bites, and minor infections.
- Inhalation/Diffusion: Used in aromatherapy for its uplifting and calming properties, or to help with respiratory congestion.
Important Safety Note: Lemon myrtle essential oil is highly concentrated and should not be ingested directly. It is for topical or aromatic use only, and always requires dilution. Pregnant individuals and those with glaucoma should exercise caution. For topical applications, a patch test is recommended to check for skin sensitivity to citral. For further research on the effects of citral, consult studies like this one on its effects against certain health conditions: Citral in lemon myrtle, lemongrass, litsea, and melissa essential oils suppress the growth and invasion of breast cancer cells.
Conclusion
In summary, the composition of lemon myrtle is a sophisticated blend of powerful natural compounds that explain its cherished status as an Australian native botanical. Dominated by an exceptionally high percentage of citral in its essential oil, the plant exhibits potent antimicrobial, antifungal, and antioxidant properties. Beyond its essential oils, the leaves are also rich in a variety of essential vitamins and minerals, including calcium, magnesium, and Vitamins C and E, along with antioxidant flavonoids like lutein. These components contribute to a diverse range of health benefits, from immune support and digestive relief to mood enhancement. The unique chemical makeup differentiates it from common citrus fruits like lemons, offering a powerful, non-acidic flavour profile that is valuable in both culinary and medicinal applications. With its multifaceted composition and proven bioactivity, lemon myrtle truly stands as the "Queen of Australian Herbs."
