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

1. Identity & Chemical Information

Indole is a bicyclic aromatic heterocycle with the IUPAC name 1H-indole. It is identified by the CAS number 120-72-9 and has a FEMA number of 2593. Other identifiers include the FL number 02.015 and CoE number 246. The molecular formula of indole is C8H7N, with a molecular weight of 117.15 g/mol. Indole's structure consists of a benzene ring fused to a pyrrole ring, which contributes to its characteristic odor profile. The presence of the nitrogen atom in the pyrrole ring is crucial for its odor properties, often described as floral and fecal, which are significant in both flavor and fragrance applications.

Citation hooks: FlavScents; PubChem; FEMA

2. Sensory Profile

Indole is known for its distinctive odor, which is often described as floral, reminiscent of jasmine, with a slightly fecal undertone. This duality makes it a powerful impact note in perfumery, where it is used to add depth and complexity. The odor threshold of indole is relatively low, making it perceptible at minute concentrations. In flavor applications, indole can contribute to the authenticity of floral and fruity profiles, often used as a background realism note.

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 during 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 qualifies it for use in "natural flavor" and "natural fragrance" designations, depending on the extraction method.

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

4. Use in Flavors

Indole is used in flavor formulations to enhance floral and fruity notes, particularly in products like candies, beverages, and desserts. It serves as a background realism note, providing depth to complex flavor systems. Typical use levels in food and beverages range from 0.1 to 1 ppm, with higher concentrations potentially leading to off-flavors due to its intense character. Indole is relatively stable under normal processing conditions but can degrade under extreme heat or acidic conditions.

Citation hooks: FlavScents; FEMA GRAS documentation; formulation literature

5. Use in Fragrances

In perfumery, indole is a critical component in floral fragrance families, such as jasmine and orange blossom. It acts as a trace realism note, adding authenticity and depth to floral compositions. Indole is typically used in concentrations ranging from 0.01% to 0.1% in fragrance formulations. Its volatility allows it to contribute to both the middle and base notes of a fragrance, providing a lasting impact.

Citation hooks: FlavScents; IFRA; fragrance chemistry texts

6. Regulatory Status (Regional Overview)

In the United States, indole is recognized as GRAS (Generally Recognized As Safe) by FEMA for flavor use. In the European Union, it is listed under Regulation (EC) No 1334/2008 with the FL number 02.015. The United Kingdom follows similar regulations post-Brexit. In Asia, indole is approved for use in Japan and China, with specific concentration limits. In Latin America, countries like Brazil and members of MERCOSUR have harmonized regulations that permit its use in both flavors and fragrances.

Citation hooks: FEMA; EFSA; national authority publications

7. Toxicology, Safety & Exposure Considerations

For oral exposure, indole's safety is supported by its FEMA GRAS status, with an acceptable daily intake (ADI) not specifically established but considered safe at typical use levels. Dermal exposure in fragrance applications is generally safe, though IFRA provides guidelines to prevent sensitization. Inhalation exposure is minimal due to its low volatility, but occupational exposure should be monitored to prevent irritation. The risk profiles for food and fragrance applications are similar, with no significant differences noted.

Citation hooks: EFSA; FEMA; PubChem; toxicology literature

8. Practical Insights for Formulators

Indole is valued for its ability to enhance floral and fruity notes in both flavors and fragrances. It synergizes well with other floral compounds like linalool and benzyl acetate. Formulators should be cautious of its potent odor, which can dominate a blend if overused. It is often under-utilized in formulations seeking natural authenticity, where its presence can significantly enhance the perception of naturalness.

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 concentration data may vary. Known data gaps are minimal, with most regulatory ambiguities resolved through harmonized international standards.

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
• If complex natural material: includes section 5a (not applicable for indole)

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 2026-10-26 12:34:23 GMT (p2)