Propyl Gallate

🌿 What is Propyl Gallate?

• Chemical structure: It’s an n-propyl ester formed from gallic acid and propyl alcohol. The chemical name is 3,4,5-trihydroxybenzoic acid. 
• Formula: C₁₀H₁₂O₅.
• MW, 212.20, melting point 150ºC, decomposes above 148ºC
• E-number: E310 in the EU, indicating its status as a food additive.
• It’s a synthetic antioxidant used to prevent oxidation of fats and oils — stopping rancidity and extending shelf life. It is soluble mainly in organic solvents such as ethyl ether, ethanol, oils and lard but also aqueous solutions of polyethylene glycol (PEG) ethers of cetyl alcohol. It has partially solubility in water and is not used in soluble systems.
• It mops up peroxides formed from lipid peroxidation (Becker & Lillian, 2007) .

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🍞 Uses in Food Products

The antioxidant is generally used in most foods, oils, fats, emulsions, waxes etc. It is partially soluble in water but also has low oil solubility. The disadvantage here is that it is not an easy ingredient to incorporate into oils and fats.  Generally, propyl gallate has a synergistic action with BHA and BHT which improves product storage stability and offers carry-through protection. Some derivatives such as the longer-chain esters including octyl and dodecyl gallates are permitted in a few countries.

1. Cheese

   • Added to processed cheeses to prevent fat oxidation, keeping flavor intact.
   • Works especially well with butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) to boost effectiveness in cheese analogues.

2. Meat products

   • Most effective in preventing rancidity in any meat product.
   • Used in cured meats, sausages, rendered fat and dried products to slow lipid oxidation, which can cause off-flavors.
   • Helps maintain the red colour of meat by preventing oxidation of myoglobin but note reactions with iron.

3. Baked goods

   • Added to pastries, cakes, and bread containing high-fat ingredients to stop oils from going rancid.
   • Extends shelf life by protecting against both autoxidation and photooxidation.

4. Snacks:

   • Found in potato chips, nuts, and popcorn — any snack using oils.
   • Often paired with other antioxidants to prevent the stale, cardboard-like taste caused by fat oxidation.

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⚗️ How Propyl Gallate Works (Reactions)

• PG acts as a free radical scavenger:

  R• (radical)+PG→R-PG (stable adduct)

• It donates a hydrogen atom from its hydroxyl group to neutralize free radicals, interrupting the chain reaction of lipid oxidation.

• In fats, it prevents the formation of hydroperoxides, which break down into aldehydes and ketones — the main cause of rancid odours.

• Will break down in most cooking and heating processes above 148ºC so is to protect ambient stored products on the whole. Not suitable for products that are fried and then stored because of the decomposition. There is no carry-through protection with heat-processed foods. This is the especially the case when the foods are alkaline as with some baked foods.
• It also complexes with iron and iron salts causing discolouration in some high iron products. Citric acid is often added to reduce the off-colour formation.

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🧪 Measurement of Propyl Gallate in Foods

• High-Performance Liquid Chromatography (HPLC) is the gold standard for measuring PG levels, ensuring it stays within legal limits.
• Sometimes, spectrophotometric methods are used to detect antioxidant activity indirectly by measuring how much PG reduces free radical levels.
• Levels are typically capped at 100–200 mg/kg of fat or oil in foods, but exact allowances depend on regional regulations (e.g., EU vs. US FDA).

🌡️ 1. High-Performance Liquid Chromatography (HPLC)

• Method: HPLC with UV detection (usually at 270–280 nm).
• Why use it: High sensitivity and selectivity — perfect for detecting PG in fats, oils, and complex food matrices (meats, cheeses, etc.).
• Procedure:
  1. Extraction: PG is often extracted using organic solvents like methanol or acetonitrile.
  2. Chromatography: A C18 reverse-phase column is standard.
  3. Detection: UV detector set to PG’s maximum absorbance wavelength.
• Limits of detection (LOD): Typically 0.01–0.1 mg/kg, depending on the equipment.

✅ Common for regulatory compliance testing.

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⚗️ 2. Gas Chromatography (GC) with Derivatization

• Method: GC with flame ionization detection (FID) or mass spectrometry (MS).
• Why use it: Suitable for volatile derivatives of PG or combined antioxidant profiling.
• Procedure:
  1. Derivatization: Since PG is not very volatile, it must be silylated (e.g., with BSTFA — N,O-bis(trimethylsilyl)trifluoroacetamide).
  2. Separation: Injected into the GC column, then separated based on volatility.
  3. Detection: Identified by retention time and/or mass spectral patterns.
• LOD: Around 0.05–0.1 mg/kg.

✅ Great for comprehensive analysis of antioxidants, including BHA/BHT.

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🔬 3. Spectrophotometry

• Method: Spectrophotometric determination using Folin-Ciocalteu reagent or 2,2-diphenyl-1-picrylhydrazyl (DPPH) assays.
• Why use it: Quick, cost-effective screening method — but less specific than chromatography.
• Procedure:
  1. Extraction: Organic solvents like methanol extract PG from the food matrix.
  2. Reaction: PG reduces a reagent like DPPH, causing a color change.
  3. Measurement: Absorbance is read at 517 nm (DPPH) or 750 nm (Folin-Ciocalteu).
• LOD: Roughly 1–5 mg/kg — less sensitive than HPLC or GC.

✅ Useful for rapid screening, but not ideal for precise quantification.

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🧪 4. Capillary Electrophoresis (CE)

• Method: CE with UV detection, sometimes paired with micellar electrokinetic chromatography (MEKC).
• Why use it: High resolution and low solvent use — good for clean food matrices.
• Procedure:
  1. Sample prep: PG extracted and diluted.
  2. Separation: Electric field separates ions based on charge and size.
  3. Detection: UV absorbance at 270 nm.
• LOD: 0.01–0.1 mg/kg.

✅ Great for labs focused on green chemistry and reducing solvent use.

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🏷️ 5. Liquid Chromatography-Mass Spectrometry (LC-MS/MS)

• Method: HPLC coupled with tandem mass spectrometry for ultra-trace analysis.
• Why use it: Extreme sensitivity and specificity — ideal for regulatory tests in low-PG foods.
• Procedure:
  1. Extraction: Solvent extraction followed by solid-phase cleanup.
  2. Separation: Reverse-phase column.
  3. Detection: Ionizes PG and identifies it by m/z ratio.
• LOD: Can detect 0.001 mg/kg or lower.

✅ The gold standard for ultra-precise analysis and identifying trace contaminants.

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🏁 When to Use Each Method

• HPLC → Best for routine lab tests and regulatory analysis.
• GC-FID/MS → Use when testing multiple antioxidants together.
• Spectrophotometry → Quick screening but less reliable for exact quantification.
• CE → A more eco-friendly, high-resolution method.
• LC-MS/MS → For ultra-sensitive, high-precision tests.

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👅 Aftertaste Concerns

• PG can leave a slightly bitter or astringent aftertaste — especially if used in excess.
• This is why it’s often combined with other antioxidants (like BHA or BHT) to lower individual concentrations and reduce sensory impact.
• Careful formulation keeps the flavor profile clean while still protecting fats and oils.

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📊 Legally Approved Levels

• EU: Up to 200 mg/kg in fat-containing foods.
• US FDA: GRAS approved. Limits vary — for instance, 0.02% of fat or oil content by weight in most foods.
• Codex Alimentarius: Provides international standards depending on food category.
• It is often used as an antioxidant in cosmetic products too to a maximum concentration of 0.1%.

References

Becker, L. (2007). Final Report on the Amended Safety Assessment of Propyl Gallate.
International Journal of Toxicology (Taylor & Francis), pp. 2689-118