Kojic Acid, Acido Kojico, 501-30-4

Kojic Acid, Acido Kojico, 501-30-4

KOJIC ACID (C₆H₆O₄)

1. Identification and Material Classification

• Chemical Name: 5-Hydroxy-2-(hydroxymethyl)-4H-pyran-4-one, 5-Hydroxy-2-hydroxymethyl-4-pyrone

• Synonyms: Kojic Acid, 5-Hydroxy-2-(hydroxymethyl)-4-pyrone, Natural Kojic Acid Powder, Anti-Dandruff Active

• CAS Number: 501-30-4

• EC Number (EINECS): 207-922-4

• Molecular Formula: C₆H₆O₄

• Molecular Weight: 142.11 g/mol

• Chemical Class: Pyrone derivative, organic acid, heterocyclic compound, chelator

• HS Code: 2932.99

• UN Number: Not applicable (not classified as hazardous material)

2. Physical Properties

2.1 General Physical Properties

2.2 Solubility Properties

2.3 Particle Characterization

• Particle size (D50): 10–100 µm (standard grade); 1–10 µm (micronized grade)

• Crystal form: Needle-like prismatic crystals

• Specific surface area (BET): 0.5–2.0 m²/g

• Bulk density (loose): 0.4–0.6 g/cm³

• Bulk density (tapped): 0.6–0.8 g/cm³

• Compressibility index: 25–35 (moderate flowability)

• Hausner ratio: 1.3–1.5

• Angle of repose: 40–50°

2.4 Hygroscopicity and Stability

• Hygroscopicity: Moderate (absorbs moisture from air, especially at high humidity)

• Deliquescence: None

• Moisture content (as supplied): ≤1.0% (typical)

• Stability (dry, 20°C, dark): 2 years (stable)

• Stability (solution, pH 4–6, 25°C): Stable (weeks to months)

• Stability (solution, pH <3 or >7, high temperature): Decomposes (color browning)

• Light sensitivity: High – discolors under light (browning)

• Oxygen sensitivity: Moderate – slow oxidation in air

• Thermal stability: Stable up to 150°C; decomposes above 150°C

Color Stability Warning: Kojic acid tends to discolor (yellow to brown) under light, heat, high pH, and oxygen. Formulations should include antioxidants (sodium metabisulfite, EDTA, BHT, tocopherol) and be stored in opaque/dark containers.

3. Chemical Properties

3.1 Molecular Structure

• Structure: 5-Hydroxy-2-(hydroxymethyl)-4H-pyran-4-one

• Molecular structure: A pyrone ring (6-membered heterocyclic oxygen-containing ring) with a ketone group (C=O at the 4-position) and two hydroxyl groups (hydroxymethyl –CH₂OH at the 2-position, phenolic OH at the 5-position).

Functional groups:

• Pyrone ring (electron-rich)

• Ketone (C=O, 4-position)

• Primary alcohol (–CH₂OH, 2-position)

• Phenolic hydroxyl (–OH, 5-position) – weak acid (pKa ~7.9)

Chelating property: Kojic acid can chelate metal ions (especially copper Cu²⁺, iron Fe³⁺, zinc Zn²⁺). This is critical for tyrosinase enzyme inhibition.

Biological origin: Kojic acid is naturally produced as a fungal metabolite by Aspergillus species (A. oryzae, A. flavus, A. tamarii) and other fungi.

3.2 Acid-Base Properties

3.3 Thermal Properties

3.4 Chemical Reactivity

• Acidic dissociation: At pH >8, the phenolic OH group loses a proton → anionic form (color change).

• Metal chelation: Forms stable complexes with copper (Cu²⁺), iron (Fe³⁺), zinc (Zn²⁺), aluminum (Al³⁺) ions (color change – reddish, brown).

• Tyrosinase inhibition: Chelates copper ions (Cu²⁺) in the active site of tyrosinase enzyme → inhibits melanin synthesis.

• Oxidation (air, light): Slowly oxidizes in air and light → discoloration (yellow → brown → black).

• pH-dependent degradation: Slow degradation at pH <3; rapid degradation at pH >7 (darkening).

• Photodegradation (UV light): Rapid degradation and discoloration under UV exposure.

• Antioxidant activity: Weak to moderate free radical scavenging activity.

• Esterification (with alcohols): Forms kojic acid esters under acid catalysis (more stable, more lipophilic derivatives).

• Glycosylation: Reacts with glucose to form kojic acid glycosides (more stable, more hydrophilic).

3.5 Kojic Acid Derivatives and Comparison

4. Commercial Grades and Specifications

5. Quality Specifications (Cosmetic/Pharmaceutical Grade)

6. Production Methods

6.1 Fermentation (Natural/Naturally Derived – Most Common Method)

• Microorganisms: Aspergillus oryzae, Aspergillus flavus, Aspergillus tamarii, Aspergillus parasiticus

• Substrates: Rice, wheat bran, corn, starch, glucose, sucrose, molasses

• Process:

  • Substrate sterilized and inoculated with Aspergillus species

  • Fermentation at 25–35°C for 5–14 days

  • Fungi ferment carbohydrates to produce kojic acid

  • Fermentation broth filtered

  • Kojic acid crystallized by cooling and acidification

  • Purified by recrystallization (water or ethanol)

• Yield: 10–30 g/L (fermentation broth)

• Purity: 99.0–99.5%

• Advantage: “Natural” labeling (preferred in cosmetics)

• Disadvantage: Lower yield, higher cost

6.2 Chemical Synthesis (Synthetic – Less Common)

• Starting materials: Glucose, fructose, or other sugars

• Reaction: Acid-catalyzed dehydration and oxidation of sugars → kojic acid

• Process: Complex multi-step synthesis (rarely industrial)

• Purity: 98.0–99.0%

• Disadvantage: Lower purity, not “natural”

7. Mechanism of Action (Functional Mechanisms)

7.1 Skin Lightening (Depigmentation) – Primary Mechanism (~90% of Use)

• Target enzyme: Tyrosinase (key enzyme in melanin biosynthesis – rate-limiting step)

• Tyrosinase role: Oxidizes tyrosine amino acid to DOPA (3,4-dihydroxyphenylalanine) and then to dopaquinone, initiating melanin synthesis.

• Kojic acid effect: Chelates copper ions (Cu²⁺) in the active site of tyrosinase.

• Chelation mechanism: Kojic acid binds Cu²⁺ ions via the hydroxyl group at the 5-position and the ketone group at the 4-position, acting as a bidentate ligand.

• Inhibition result: Tyrosinase becomes inactive and cannot oxidize tyrosine.

• Final outcome: Reduced melanin production → skin lightening, fading of age spots, sun spots, melasma, hyperpigmentation, and post-acne dark marks.

• Tyrosinase inhibition potency (IC₅₀): Kojic acid ≈ 1–5 µg/mL (depending on enzyme source).

Comparison with other skin lighteners:

• Hydroquinone: Stronger but more toxic, banned in many countries

• Arbutin: Weaker (IC₅₀ ≈ 50–100 µg/mL) but more stable

• Glabridin (licorice root): Similar strength (IC₅₀ ≈ 1–2 µg/mL), more expensive

• Vitamin C (ascorbic acid): Weaker (IC₅₀ ≈ 100–500 µg/mL), unstable

7.2 Antioxidant Mechanism (Free Radical Scavenging)

• Free radical scavenging: Kojic acid neutralizes reactive oxygen species (ROS: hydroxyl radicals, superoxide radicals, peroxyl radicals).

• UV protection: Reduces oxidative stress caused by UV radiation.

• Result: Prevents dull appearance caused by free radicals, protects skin against UV damage (synergistic with sunscreens).

7.3 Antifungal and Antimicrobial Mechanism (Secondary Use)

• Target: Yeast and fungal cell walls (athlete’s foot – Trichophyton, Candida species).

• Metal chelation: Inhibits fungal enzymes by chelating metal cofactors (copper, iron).

• Cell wall permeability: May increase fungal cell wall permeability.

• Result: Inhibits growth of yeast and fungal infections.

Antifungal activity (MIC values):

• Candida albicans: 100–500 µg/mL

• Trichophyton rubrum (athlete’s foot): 50–200 µg/mL

• Malassezia species (dandruff): 100–500 µg/mL

7.4 Anti-inflammatory Mechanism (Mild)

• Cytokine reduction: Decreases production of pro-inflammatory cytokines (IL-1β, IL-6, TNF-α).

• Result: Reduces skin redness and inflammation.

8. Application Areas

8.1 Cosmetics and Skin Care – Major Use (~90%)

Formulation notes:

• Kojic acid is unstable (discolors under light, air, high pH).

• Stabilization methods: antioxidants (sodium metabisulfite, EDTA, BHT, tocopherol), pH 4–6, opaque packaging, avoid >50°C.

• Compatible with niacinamide, arbutin, glycolic acid, salicylic acid.

• Incompatible with hydroquinone, high vitamin C, retinol, high pH, iron compounds.

8.2 Dermatology (Pharmaceutical/Medical)

• Hyperpigmentation treatment creams (melasma, age spots, solar lentigo) – 1–2%

• Combination therapy (kojic acid + tretinoin + mild steroid) – prescription

• Hydroquinone alternative – safer, OTC in most countries

• Post-inflammatory hyperpigmentation (PIH) – 1–2%

• Chemotherapy-related hyperpigmentation – 1–2%

8.3 Hair Care (Salon Products)

• Curling products (perm solutions) – preservative, 0.05–0.1%

• Hair-lightening shampoos – melanin inhibition, 0.1–0.5%

• Anti-dandruff shampoos – antifungal activity, 0.1–0.5%

8.4 Foot Care (Antifungal Products)

• Athlete’s foot creams – antifungal, 0.5–1.0%

• Anti-fungal creams (foot, nail) – 0.5–1.0%

• Antifungal powders – 0.5–1.0%

8.5 Food Industry (Limited Use)

• Food antioxidant (color preservative) – prevents browning in cut fruits, 0.01–0.1% (surface application), approved in Japan

• Seafood preservative – prevents discoloration, 0.01–0.05% (dipping)

• Wine production – reduces browning, 10–50 mg/L

9. Kojic Acid vs. Other Skin Lighteners – Comparison

10. Cosmetic Formulation Guide

• Typical concentrations:

  • Creams/serums: 1–2%

  • Lotions: 0.5–1%

  • Toners: 0.2–0.5%

  • Eye creams: 0.5–1%

• Stability requirements:

  • Dissolve in water phase at 40–50°C

  • Maintain pH 4–6 (optimal 5)

  • Add antioxidants (sodium metabisulfite, EDTA, tocopherol, BHT)

  • Use opaque packaging, store <25°C, avoid oxygen/light

11. Toxicology and Safety

• Acute toxicity: Oral LD₅₀ (rat) >2000 mg/kg; dermal LD₅₀ >2000 mg/kg

• Irritation: Mild skin/eye irritant at high concentrations (>2%)

• Chronic toxicity: No carcinogenicity, no reproductive toxicity, no teratogenicity

• Special concerns: Rare allergic contact dermatitis, discoloration in formulations, avoid hydroquinone combination

GHS Classification:

• Acute toxicity (oral): Category 4 – H302

• Eye irritation: Category 2 – H319

• Skin irritation: Category 2 (≥2%) – H315

NFPA Rating:

• Health: 1 (slight hazard)

• Flammability: 1 (slight hazard – combustible dust)

• Reactivity: 0 (stable)

12. Safety Measures and PPE

• Respiratory protection: P1/P2 dust mask

• Eye protection: Safety goggles

• Gloves: Nitrile or latex

• Clothing: Lab coat, protective wear

• Storage: 10–25°C, <60% humidity, opaque airtight containers, away from oxidizers and metals (iron, copper).

• Shelf life: 2 years (sealed), 1 year (opened).

13. Environmental Fate

• Biodegradable (>70% in 28 days, OECD 301)

• Low aquatic toxicity (LC₅₀ fish 100–500 mg/L)

• Low bioaccumulation potential (log P -0.9 to -0.5)

• WGK Germany: 1 (low hazard to water)

14. Storage and Shelf Life

• Storage temperature: 10–25°C (do not exceed 30°C)

• Humidity: <60%

• Protect from light and oxygen

• Suitable containers: HDPE, LDPE, PP, glass, stainless steel (not iron or copper)

• Shelf life: 2 years unopened, 1 year after opening