Antioxidants and Shelf Life of Foods - Food Shelf Life Stability: Chemical, Biochemical, and Microbiological Changes - page 177

Secondary Antioxidants
Secondary antioxidants function by decomposing lipid peroxides into more stable
end products. This group includes thiopropionic acid and it derivatives.
Synergists
Synergistic antioxidants are primarily oxygen scavengers and metal chelators. They
operate by a number of mechanisms including regeneration of primary antioxidants
by donating hydrogen atoms to phenoxyl radicals or by proving a more stable acid
environment for these antioxidants. Ascorbic acid, sulfites, and erythorbic acid are
examples of oxygen scavengers, while EDTA, citric acid, and phosphates function
as metal chelators. Compounds listed under miscellaneous are capable of functioning
as primary antioxidants and synergists ( Figure 6.2 ).
A large number of compounds found in animal and plant tissues, also available
as synthetic molecules, are used in food applications. These include tocopherols and
ascorbic and citric acids, often used in combination with each other or other anti-
oxidants to take advantage of synergistic effects. 16 Although commonly used for
years as a spice or flavoring agent, extracts of rosemary leaves have become the
subject of increasing interest as inhibitors of lipid oxidation, and are used commer-
cially. Rosemary extract contains many different compounds including carnosol,
carnosic acid, and rosmanol thought to act synergistically as antioxidants and now
available commercially. 23,24
S YNTHETIC
The most commonly used antioxidants are butylated hydroxyanisole (BHA), buty-
lated hydroxytoluene (BHT), tert -butyl hydroquinone (TBHQ), and propyl gallate
(PG), often used in combinations. Various regulations exist in different countries to
control the amount or application of use of food antioxidants. In Canada, TBHQ
has only recently been permitted for use in foods, even though it has been used for
a number of years in other countries. Toxicological data have led to concerns
regarding the potential toxicity of BHA such as the development of carcinoma in
rodents if consumed routinely. 25 Some of these studies were criticized for their use
of excessive concentrations and thereby overestimating the hazards. Nevertheless,
there is a worldwide trend to reduce or avoid use of synthetic food antioxidants.
Commercial formulations of synthetic antioxidants are shown in Table 6.2 .
BHA (Butylated Hydroxyanisole) and BHT
(Butylated Hydroxytoluene)
The most widely used synthetic antioxidants are BHA and BHT, both monohydroxy
phenols ( Figure 6.4 ). BHA is a mixture of two isomers, 3-tertiary-butyl-4-hydroxy-
anisole (90%) and 2-tertiary-butyl-4-hydroxyanisole (10%). Both antioxidants are
fat soluble and exhibit good carry-through effects, although BHA is slightly better. 20
BHT is particularly effective in protecting animal fats from oxidation while BHA
is more effective in vegetable oils. BHA is particularly effective in protecting the