Antioxidants are chemical compounds that provide stability to fats and oils by delaying oxidation reactions. Antioxidants do not stop oxidation; they merely slow the reaction down.

Generally, antioxidants only involve oil-soluble ingredients but there are some water-soluble antioxidants such as ascorbates.

What causes oxidation?
The degree of saturation of the fat or oil. Saturated fats such as animal fats tend to be much more stable than unsaturated vegetable oils. The greater the number of unsaturated carbon bonds, the more sites there are for oxidation.
Catalysts such as metal ions significantly influence oxidation. These may be found in other ingredients, processing equipment or even packaging.
Oxidation is also influenced by exposure to light, heat, oxygen or enzyme activity.
While manufacturers can minimise the introduction of metal ions, and remove oxygen with technologies such as gas flushing, rancidity will usually occur in food products containing unsaturated fats, especially once the oxidative resistance of products is broken down.

Oil-soluble antioxidants can be grouped into two categories:
Natural antioxidants
Synthetically manufactured antioxidants

Water-soluble antioxidants

Ascorbic acid is a valuable antioxidant in water-based systems and will preferentially degrade to protect the food system, especially where there is the risk of enzymatic browning. However, in some systems it can degrade to furfural and form brown pigments, so shelf life testing is imperative. Ascorbic acid is readily soluble in water, but will degrade quickly to dehydroascorbic acid (DHA), when mixed with oxygen.

Sodium Erythorbate is the sodium salt of iso-ascorbic acid (also known as erythorbic acid) and can be used to slow the rate of enzymatic browning in food products where the acidic impact of ascorbic acid is not appropriate. In meat curing, it controls and accelerates the nitrite curing reaction and maintains the bright red colour in meats. It is used in frankfurters, hams and bacon and is often used in guacamole, beverages and fruit products.

Citric acid can also act as a sequesterant for metals and can reduce the rate of oxidation by binding with potential oxidation catalysts.

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