Vitamin C As An Antioxidant

Vitamin C (ascorbic acid) is a water-soluble antioxidant widely used in food systems for its ability to prevent oxidation — but it can also act as a prooxidant under certain conditions. 

🌿 Vitamin C as an Antioxidant in Food Systems:

1. Prevents lipid oxidation:

   • It scavenges free radicals (like superoxide and hydroxyl radicals) that cause fats and oils to spoil.
   • Used in meat products (sausages, cured meats) to prevent rancidity.

2. Enhances colour stability:

   • Maintains the bright red colour of fresh meat by reducing metmyoglobin back to oxymyoglobin.
   • Prevents browning in fruits and vegetables by inhibiting polyphenol oxidase (PPO) activity.
   • Part of the anti-browning activity is due to reduction of phenoxyl radicals and quinone versions of phenolics to the colourless diphenols in a coupled oxido-reduction reaction (Louarme & Billaud, 2012).

3. Preserves flavour:

   • Protects essential oils and aromas in fruit juices and soft drinks by preventing oxidative damage.

4. Works synergistically with other antioxidants:

   • Often combined with vitamin E (a fat-soluble antioxidant) — vitamin C regenerates oxidized vitamin E, boosting its effectiveness.
   • Used with citric acid to enhance antioxidant potential in foods and drinks.

⚡ Vitamin C as a Prooxidant:

Ironically, vitamin C can switch sides — acting as a prooxidant in certain conditions. Ascorbate accelerates lipid peroxidation because of its ability to reduce iron to the ferrous state as we describe below but when in high enough concentration will inhibit lipid oxidation by inactivating fee radicals (Decker & Xu, 1998). 

1. In the presence of transition metals (like iron or copper): 

   • When free metal ions (Fe²⁺ or Cu²⁺) are present, vitamin C reduces them to more reactive forms, triggering Fenton reactions.
   • This generates hydroxyl radicals — accelerating lipid oxidation and protein degradation.
   • Happens in some fortified cereals, meats, and dairy products.

2. High oxygen environments:

   • In high-oxygen packaging (like some meat packaging systems), vitamin C can accelerate oxidative stress, breaking down quickly and forming harmful radicals.

3. At high concentrations:

   • Excessive vitamin C in certain foods can paradoxically drive oxidation, especially in combination with unsaturated fats and metal ions.
   • High levels of vitamin C above 200ppm have a flavour impact – nothing to do with its other functional properties but because it is an acid that contributes to subtle changes in pH.

🌟 Practical Applications in Food

• Antioxidant: Used in beverages, cured meats, and fruit preserves to prevent spoilage.
• Prooxidant risk mitigation: Managed by adding chelating agents (like citric acid or EDTA) to bind free metal ions, keeping vitamin C’s antioxidant role stable.

References

Decker, E. A., and Z. Xu. 1998. Minimizing rancidity in muscle foods. Food Technol. 52 pp. 54–59.

Louarme, L. and Billaud, C. (2012). Evaluation of ascorbic acid and sugar degradation products during fruit dessert processing under conventional or ohmic heating treatment. LWT – Food Science and Technology 49 pp. 184−187 .