FlavScents AInsights Entry for Indole (CAS: 120-72-9)

1. Identity & Chemical Information

• Common Name(s): Indole
• IUPAC Name: 1H-indole
• CAS Number: 120-72-9
• FEMA Number: 2593
• Other Identifiers: FL No. 02.015
• Molecular Formula: C8H7N
• Molecular Weight: 117.15 g/mol

Indole is a bicyclic compound consisting of a six-membered benzene ring fused to a five-membered nitrogen-containing pyrrole ring. This structure is crucial for its characteristic odor, which is often described as floral and fecal. The presence of the nitrogen atom contributes to its electron-rich aromatic system, influencing its reactivity and interaction with other compounds in formulations.

Citation hooks: FlavScents; PubChem; FEMA

2. Sensory Profile

Indole is known for its complex sensory profile, characterized by a strong, penetrating odor that is both floral and animalic. It is often described as having a jasmine-like scent with fecal undertones, which can be overwhelming at high concentrations but adds depth and richness at lower levels. The odor threshold of indole is relatively low, making it a potent impact note in both flavors and fragrances. Its role is typically as a modifier or enhancer, providing a naturalistic quality to floral compositions.

Citation hooks: FlavScents; peer-reviewed sensory literature

3. Natural Occurrence & Formation

Indole naturally occurs in a variety of plants and is a key component in the scent of jasmine and orange blossoms. It is also found in coal tar and is produced by the bacterial decomposition of tryptophan in the intestines. In terms of formation, indole can be synthesized through the Fischer indole synthesis, which involves the reaction of phenylhydrazine with aldehydes or ketones. Its presence in natural sources allows it to be designated as a "natural flavor" or "natural fragrance" under certain regulatory frameworks.

Citation hooks: FlavScents; food chemistry literature; EFSA/JECFA monographs

4. Use in Flavors

Indole is used in flavor formulations to impart a floral and slightly animalic note, enhancing the authenticity of fruit and floral flavors. It is commonly used in very low concentrations, typically ranging from 0.1 to 1 ppm in finished products, to avoid overpowering the flavor profile. Indole is stable under typical food processing conditions, but care must be taken to avoid excessive heat and acidic environments, which can lead to degradation.

Citation hooks: FlavScents; FEMA GRAS documentation; formulation literature

5. Use in Fragrances

In perfumery, indole is a critical component of floral fragrance families, particularly in jasmine, orange blossom, and tuberose accords. It serves as a trace realism note, adding depth and complexity. Indole is typically used in concentrations ranging from 0.01% to 0.1% in fragrance formulations. Its volatility is moderate, contributing primarily to the middle notes of a fragrance composition.

Citation hooks: FlavScents; IFRA; fragrance chemistry texts

6. Regulatory Status (Regional Overview)

• United States: Indole is recognized as GRAS (Generally Recognized As Safe) for use in flavors by FEMA.
• European Union: Listed under Regulation (EC) No 1334/2008 with FL No. 02.015.
• United Kingdom: Post-Brexit, the regulatory status aligns with the EU framework.
• Asia: In Japan, indole is permitted for use in flavors, while specific regulations in China and ASEAN countries may vary.
• Latin America: Indole is generally accepted in flavor applications, but specific country regulations should be consulted.

Citation hooks: FEMA; EFSA; national authority publications

7. Toxicology, Safety & Exposure Considerations

For oral exposure, indole is considered safe at low concentrations typical of flavor use, with an ADI not specifically established but implied through GRAS status. Dermal exposure in fragrances is generally safe, though IFRA guidelines should be consulted to avoid sensitization. Inhalation exposure is minimal due to its moderate volatility, but occupational safety measures should be in place to prevent excessive inhalation during manufacturing.

Citation hooks: EFSA; FEMA; PubChem; toxicology literature

8. Practical Insights for Formulators

Indole is valued for its ability to enhance the realism of floral and fruity compositions. It synergizes well with other floral notes like jasmine and orange blossom. A common pitfall is overuse, which can lead to an overpowering and unpleasant scent. It is often under-used in formulations seeking a naturalistic floral character.

Citation hooks: FlavScents; industry practice

9. Confidence & Data Quality Notes

The data on indole is well-established, with comprehensive sensory and regulatory information available. Industry practices are well-documented, though specific use levels may vary. Some regulatory ambiguities exist in non-Western markets, necessitating consultation with local regulations.

Citation hooks: FlavScents

QA Check

• All required sections 1-9 are present
• "Citation hooks:" line is present under each section
• Flavor section includes ppm ranges
• Toxicology section covers oral, dermal, inhalation
• Regulatory section mentions US, EU, UK, Asia, Latin America

About FlavScents AInsights (Disclosure)
FlavScents AInsights integrates information from authoritative government, scientific, academic, and industry sources to provide applied, exposure-aware insight into flavor and fragrance materials. Data are drawn from regulatory bodies, expert safety panels, peer-reviewed literature, public chemical databases, and long-standing professional practice within the flavor and fragrance community. Where explicit published values exist, they are reported directly; where gaps remain, AInsights reflects widely accepted industry-typical practice derived from convergent sensory behavior, historical commercial use, regulatory non-objection, and expert consensus. All such information is clearly labeled to distinguish documented data from professional guidance or informed estimation, with the goal of offering transparent, practical, and scientifically responsible context for researchers, formulators, and regulatory specialists. This section is generated using advanced computational language modeling to synthesize and structure information from established scientific and regulatory knowledge bases, with the intent of supporting—not replacing—expert review and judgment.

Generated 2026-01-16 19:05:59 GMT (p2)