Antioxidants

Antioxidants function by interfering with the chain reaction. If the number of free radicals can be kept low enough, oxidation will not occur. The following is a model for the type of compound that can function effectively as an antioxidant:

In order to function well as an antioxidant a molecule must:

React with free radicals more rapidly than the free radicals react with lipid.
The products of the reaction with free radicals must not be pro-oxidant.
The molecule must be lipid soluble.

The free radicals formed by conjugated molecules can exist in many resonant structures as shown below:

Where R* is equal to ROO*

This molecule reacts very rapidly with free radicals because of the low energy required to remove the hydrogens located alpha to the double bonds. The free radical generated does not initiate oxidation because of the resonance stabilization. The problem with this molecule (hydraquinone) is that it is not lipid soluble. Groups may be added to the ring that will increase lipid solubility without interfering with the molecules antioxidant properties. The following are some naturally occurring and synthetic antioxidants utilized in foods:

NDGA

4,4í (2,3 dimethyl tetramethylene dipyrochatechol)

Alpha Tocopherol

Other isomers of tocopherol also function well as antioxidants.

BHA

BHT

Propyl Gallate

TBHQ

Tertiary butylhydroquinone

BHA

Butylated hydroxy anisole is a mixture of two isomers. Referred to as a 'hindered phenol' because of the proximity of the tertiary butyl group to the hydroxyl group. This may hinder the effectiveness in vegetable oils, but increase the 'carry through' potency for which BHA is known.

Propyl Gallate

Three hydroxyl groups make it very reactive. Lower solubility. Tend to chelate trace minerals such as iron and form colored complexes. Are heat labile, especially under alkaline conditions.

BHT

Butylated hydroxy toluene is also a 'sterically hindered' phenol Susceptible to loss through volatilization in high temperature applications.

TBHQ

Tertiary-butylatedhydroquinone is an extremely potent antioxidant. Had been used extensively in non food applications prior to gaining approval in food.

Combinations

Antioxidants are usually combined to take advantage of their differing properties. For example BHA may be combined with PG and citric acid. The citrate chelates metals, the propyl gallate provides a high level of initial protection while the BHA has good carry through properties.

Reasons for Combinations

Take advantage of different properties
Allow for better control and accuracy
May provide synergistic effects
Combinations may provide more complete distribution in some foods
More convenient to handle

Stability of Bakery Products (AOM - Days of stability)

BHA

Uses: Lard, shortenings, vegetable oils, cereals, package liners, potato products, dry soups, chewing gum, etc. Usually in combination with other primary antioxidants.

BHT
Uses: Lard, shortening, vegetable oils, cereals, package liners, animal feeds, etc. Used alone and in combination with BHA or PG and citric acid.

PG
Uses: Lard, shortening, vegetable oils, cereals, animal feeds, etc. Usually used in combination with BHA or BHT and citric acid.

TBHQ
Uses: Lard, cottonseed oil, potato chips, corn flakes

Uses of Antioxidants

Fats and oils (less effective in higher polyunsaturates)
Foods made with fats (potato chips, nuts, candies, pre-mixes, frozen pies)
Foods with fatty constituents (peppers, other spices, cereals, dehydrated vegetables, citrus oils, chewing gum)
Feed and forage (preserve vitamin A and carotene)

A number of spices have been shown to inhibit oxidation in certain food systems. This activity can generally be related back to the presence of phenolic compounds such as:

Eugenol
carnosol
Rosmanol
Rosmariquinone

Natural Antioxidants

Should not cause off flavors of colors
Must be lipid soluble
Must be non toxic
Should have carry through properties
Must be cost-effective

Sources

A number of spices and other plant products contain phenolic compounds that may have significant antioxidant properties. Some examples of these compounds follow.

Rosmariquinone

Sesame

Contains sesamol. Reported to be more effective in lard than BHA or BHT.

Oats

Oats have been long recognized to have antioxidant properties. Over 25 phenolic compounds have been identified in oats. Many derived from caffeic and ferulic acid.

Phospholipids have been reported to behave both as antioxidants and proxidants. Most of the antioxidant effect noted appears to be due to chelation of metal ions.

Ascorbic Acid

Vitamin C can have antioxidant activity under some circumstances. It can act:

As a scavenger for oxygen
As a hydrogen donor to phenolics
Can act as a synergist with some AO

When ascorbic acid reacts with some metals, it will reduce them and allow them to act more effectively as proxidants.

Flavonoids

A number of flavonoids have been demonstrated to have antioxidant properties. Quercitrin and rutin have been shown to be effective in lard and milk fat. These compounds may have colors and flavors. Quercetin is shown below:

Effective antioxidants in the range of from 0.02 to 0.10% in several lipids. In lard, d -tocopherol was most effective at 0.02%. Have good carry through properties in crackers, pastry and potato chips produced with lard. Tocopherols also serve as quenchers of singlet oxygen. Thus there may be two mechanisms. The level of tocopherol use in foods is limited to approximately the amounts normally found in the food product. At higher concentrations, the tocopherols may be oxidized more rapidly than the other lipids and actually become proxidant.