Ascorbic acid (CAS 50-81-7, C6H8O6, MW 176.12) is vitamin C in its pure form and one of the most widely used antioxidants in the food industry. It protects color, flavor and nutritional value across beverages, meat, bakery, fruit and oil products. This guide covers how ascorbic acid works as a food antioxidant, the application doses used in practice, the grades available, and what buyers should specify on a Certificate of Analysis (COA).
1. Why Ascorbic Acid Is a Food Antioxidant
Ascorbic acid is a six-carbon lactone with a 2,3-enediol structure that makes it a powerful reducing agent. It scavenges reactive oxygen species (ROS), reduces oxidized species, and is consumed as it does so. In food systems it acts in four ways:
- Oxygen scavenging: reacts with dissolved oxygen in beverages and packaged foods, slowing oxidative spoilage.
- Free-radical termination: donates hydrogen atoms to quench peroxyl and hydroxyl radicals before they attack lipids.
- Reducing agent: keeps metal ions such as iron and copper in their reduced state, limiting metal-catalyzed oxidation.
- Regeneration of tocopherol: reduces the tocopheryl radical back to active vitamin E, extending the protection of oils (synergistic effect).
Because it is water-soluble and non-toxic at food-use levels, ascorbic acid is accepted worldwide as a general-purpose antioxidant (FDA 21 CFR 182.3013, GRAS; EU additive E300).
2. Key Physical and Chemical Properties
| Property | Value |
|---|---|
| Molecular formula | C6H8O6 |
| Molecular weight | 176.12 g/mol |
| Appearance | White to slightly yellow crystalline powder |
| Melting point | 190-192 °C (decomposes) |
| Solubility in water | Approx. 333 g/L at 20 °C; freely soluble |
| pKa (25 °C) | 4.17 (first), 11.57 (second) |
| Optical rotation [α]D | +20.5 to +21.5 ° (L-ascorbic acid) |
| Redox potential | +0.08 V vs SHE at pH 7 (ascorbate/ascorbyl radical) |
The biologically active form is L-ascorbic acid; the D-isomer has negligible vitamin activity. The related compound erythorbic acid (D-isoascorbic acid, CAS 89-65-6) is an inexpensive antioxidant without vitamin C activity, often used in cured meats.
3. Application by Food Category
3.1 Beverages
In juices, soft drinks and functional drinks, ascorbic acid is added at roughly 100-500 mg/L. It protects natural colors, reduces browning from polyphenol oxidation, and preserves added flavors. In oxygen-sensitive drinks it acts as a dissolved-oxygen scavenger, especially when combined with nitrogen flushing or aseptic filling.
3.2 Meat and cured products
Ascorbic acid (or sodium erythorbate) is used at 0.02-0.05% (200-500 ppm) in sausages, ham and bacon. It accelerates nitrite-to-NO conversion, stabilizes the pink cured color, and inhibits formation of nitrosamines by reducing residual nitrite. Sodium ascorbate is often preferred in this application because it does not lower pH.
3.3 Fruit and vegetable processing
Dipping cut fruit in 0.1-1% ascorbic acid solutions prevents enzymatic browning by reducing the o-quinones produced by polyphenol oxidase, and by lowering surface pH. It is used on apple slices, avocado, mushrooms and fresh-cut produce to extend shelf life while maintaining color.
3.4 Bakery and flour
In bread and bakery products, ascorbic acid is a flour improver at 10-50 ppm on flour weight (0.001-0.005%). It strengthens gluten through oxidation of thiol groups, improving dough tolerance, loaf volume and crumb structure.
3.5 Oils and emulsions
In vegetable oils and emulsions, ascorbic acid at 0.01-0.05% works with tocopherols to delay rancidity. For fatty systems, the lipophilic derivative ascorbyl palmitate (E304) is more effective.
3.6 Beer, wine and seafood
Brewers add 10-50 ppm to remove oxygen before packaging, reducing haze and staling. Winemakers use it to protect aroma and color of white wines. In frozen and canned seafood, 0.1-0.5% dips prevent lipid oxidation and color loss.
4. Grades and Specifications
| Grade | Typical assay | Standards | Main use |
|---|---|---|---|
| Food grade | 99.0-100.5% | FCC, E300 | Food and beverage antioxidant, fortification |
| Pharmaceutical grade | 99.0-100.5% | USP, EP, JP | API, formulations, parenteral products |
| Feed grade | 98%+ | Feed additive spec | Animal nutrition, premixes |
Typical impurity limits to verify on the COA: heavy metals ≤10 ppm (lead ≤2 ppm), arsenic ≤3 ppm, sulfate ash ≤0.1%, loss on drying ≤0.4%. Particle size (mesh 20-100) matters for blending uniformity in premixes and tablets.
5. Choosing the Right Form
| Form | CAS | Characteristic | Best for |
|---|---|---|---|
| Ascorbic acid | 50-81-7 | Acidic, water-soluble | General antioxidant, pH control, baking |
| Sodium ascorbate | 134-03-2 | Neutral pH, no acid taste | Beverages, cured meats, supplements |
| Calcium ascorbate | 5743-27-1 | Neutral, adds calcium | Fortified foods, produce dips |
| Ascorbyl palmitate | 137-66-6 | Lipophilic, oil-soluble | Oils, fats, emulsions (E304) |
| Sodium erythorbate | 6381-77-7 | No vitamin activity, cheaper | Cured meats, cost-sensitive antioxidant |
6. Buying Guide
- Specify grade and standard (FCC vs USP/EP) and the assay range on the COA.
- Check heavy-metal and arsenic limits; require a batch COA with measured values.
- Packaging: 25 kg fiber drums or bags with PE liner; food-grade material handling.
- Storage: sealed, cool (<25 °C), dry (RH <60%), away from light and oxidizers.
- Typical shelf life: 24-36 months from manufacture when stored correctly.
- For premix use, confirm particle size and flowability; ask about anti-caking treatment if needed.
7. Safety and Regulatory Notes
- FDA: ascorbic acid is GRAS (21 CFR 182.3013); EU additive E300 with no specified ADI limit at food-use levels.
- Handling: dust may irritate eyes; use local exhaust and personal protective equipment; MSDS required per region.
- Pharma-grade material must meet monograph impurity profiles (USP/EP) and be produced under GMP.
8. FAQ
What is the difference between ascorbic acid and citric acid?
Both are acids and chelating agents, but ascorbic acid is a reducing antioxidant (vitamin C) that quenches radicals and scavenges oxygen; citric acid mainly chelates metal ions and adjusts pH. They are often used together.
Is ascorbic acid the same as vitamin C?
Yes. L-ascorbic acid is vitamin C. Erythorbic acid (isoascorbic acid) is a stereoisomer without significant vitamin activity, used only as an antioxidant.
Why does ascorbic acid darken in solution?
In water it oxidizes to dehydroascorbic acid and further degradation products; exposure to oxygen, light, heat and metal ions accelerates this. Use oxygen control and keep solutions cold.
How much ascorbic acid should I add to juice?
Typically 100-500 mg/L; confirm by shelf-life trials, since excess can cause off-taste and pro-oxidant effects in some systems.
9. References and Further Reading
- PubChem CID 54670067, Ascorbic acid: physical and chemical properties (accessed via PubChem REST API).
- FCC (Food Chemicals Codex) monograph, Ascorbic Acid.
- USP-NF / Ph. Eur. monographs, Ascorbic Acid.
- FDA 21 CFR 182.3013 (GRAS status).
- EFSA re-evaluation of ascorbic acid (E300) as a food additive.
This article is published for industrial and technical reference by PolyblueChem. Verify all values against the supplier’s COA and the applicable standard before specification.
PolyblueChem supplies ascorbic acid (vitamin C, CAS 50-81-7) in food, pharmaceutical and feed grades with COA and MSDS. Contact us for specifications and quotations.