The root of Eurycoma longifolia (Tongkat Ali) consists of two chemically distinct tissues:
- Root bark, comprising the periderm, cork, phloem, and outer cortex.
- Inner root wood (xylem), the dense woody core that remains after the bark is removed.
Although most commercial Tongkat Ali products are manufactured from the woody xylem because of its stability during storage, recent phytochemical analyses indicate that the root bark is considerably richer in several important bioactive compounds, including eurycomanone.
Eurycomanone Distribution
A 2015 study by researchers at Universiti Teknologi Malaysia quantified eurycomanone in different parts of the plant.
"The highest concentration of eurycomanone content in parts of Tongkat ali (TA) were 6.0568 (leaves), 0.1415 (twigs), 0.0365 (top of stems), 0.0633 (middle of stems), 0.0673 (bottom of stems), 0.3533 (roots) and 5.1137 µg/mL (root barks)."
-- Jurnal Teknologi, 2015
| Plant part | Eurycomanone (µg/mL) |
|---|---|
| Leaves | 6.0568 |
| Root bark | 5.1137 |
| Root (main woody portion) | 0.3533 |
| Twigs | 0.1415 |
| Bottom stem | 0.0673 |
| Middle stem | 0.0633 |
| Top stem | 0.0365 |
These results show that:
- Root bark contains approximately 14–15 times more eurycomanone than the woody root.
- Leaves contain approximately 17 times more eurycomanone than the woody root.
- Contrary to long-standing assumptions, the woody taproot is not the richest source of eurycomanone.
Root Bark
The bark is the metabolically active outer layer of the root and serves as the plant's primary defense against soil microorganisms, insects, and environmental stress.
Compared with the inner wood, the root bark is characterized by:
- Very high eurycomanone concentration
- High concentrations of other quassinoids
- Higher levels of canthin-6-one alkaloids
- Higher levels of β-carboline alkaloids
- Greater concentrations of phenolic compounds
- Higher tannin content
- Lower amounts of cellulose and lignin
These compounds are associated with the bark's defensive role and contribute to its strong bitterness.
Inner Root Wood (Xylem)
The xylem consists mainly of structural tissue responsible for water transport and mechanical support.
Its composition is dominated by:
- Cellulose
- Hemicellulose
- Lignin
- Structural polysaccharides
Although the xylem still contains quassinoids such as eurycomanone, their concentration is substantially lower than in the bark.
Comparison of Compound Classes
| Compound class | Root bark | Root wood (xylem) |
|---|---|---|
| Eurycomanone | Very high | Low |
| Other quassinoids | High | Moderate |
| Canthin-6-one alkaloids | High | Moderate |
| β-Carboline alkaloids | High | Moderate |
| Phenolic compounds | High | Low |
| Tannins | High | Very low |
| Cellulose | Low | Very high |
| Hemicellulose | Moderate | High |
| Lignin | Moderate | Very high |
| Structural fibre | Low | Very high |
Why Commercial Products Often Use the Root Without the Bark
Despite its lower concentration of eurycomanone, commercial Tongkat Ali products are often manufactured from peeled root (xylem). This appears to be driven more by practical considerations than by phytochemical richness.
The root bark begins to deteriorate relatively quickly once the root dies or is harvested. It is more susceptible to microbial decomposition, moisture loss, and physical damage during handling and storage.
The woody xylem, by contrast:
- Is mechanically stronger.
- Resists fungal and bacterial degradation more effectively.
- Stores well for extended periods.
- Can be transported and processed with less deterioration.
As a result, producers frequently remove the bark before drying and processing the roots, yielding a more stable raw material even though it contains substantially less eurycomanone.
Conclusion
Current evidence indicates that the root bark is chemically richer than the woody xylem in terms of medicinal secondary metabolites, particularly eurycomanone. According to the 2015 Universiti Teknologi Malaysia study, root bark contains approximately 5.11 µg/mL of eurycomanone, compared with 0.35 µg/mL in the woody root, representing roughly a 14-fold difference.
Nevertheless, the xylem remains the preferred commercial raw material because of its superior storage stability and resistance to deterioration after harvest. Thus, the widespread use of peeled root in the Tongkat Ali industry likely reflects considerations of processing and preservation rather than the highest concentration of bioactive constituents.
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