Synthetic and natural antioxidant additives in food stabilization: current applications and future research - Oxidation in Foods and Beverages and Antioxidant Applications - page 307

Fig. 12.22 The structures of 5 -avenasterol and linallyl oleate.
Tian and White (1994) found that oil extracted from bread cubes fried in
soybean and cottonseed oils containing a sterol fraction extracted from oats had
significantly lower peroxide values and a higher linoleic/palmitic acid ratio than
did control oils or oils containing polydimethylsiloxane stabilizers. Yan and
White (2002) and Onal-Ulusoy et al. (2005) stabilized oil systems using
structurally related linalool derivatives. Both the plant sterols and linallyl esters
contain active allylic sites that might form relatively stable carbon-centered free
radicals with stability and reactivity reminiscent of the chemistry of
benzofuranones used in polymers. This mechanism is highly speculative and
has not been proved. The structures of 5 -avenasterol, an allylically stabilized
5 -avenasterol radical and linallyl oleate are shown in Fig. 12.22.
12.6.3 Secondary antioxidant comparisons
In the plastics industry, highly reactive phosphite stabilizers are routinely used
as secondary antioxidants, where they perform particularly well in helping to
control viscosity during melt processing. They react stoichiometrically with
hydroperoxides and therefore play a smaller role in enhancing the long-term
stability of the polymer (Schwarzenbach et al., 2001). Because of their toxicity
and reactivity, phosphites cannot be used in foods. Some sulfur compounds,
though overtly less reactive than phosphites, can serve a hydroperoxide-
decomposing function in both non-food and food applications. Denison (1944)
studied the oxidative stability of crude oil-derived lubricating oils and found that
the hydrocarbon base `possessed negligible resistance to oxidation' after
removal of the 2±20% sulfur compounds present in the typical commercial oils.
In plastics, thiodipropionic acid and its long-chain esters are antioxidant
common additives. Each thiodipropionic acid molecule can consume multiple
hydroperoxides as shown in Fig. 12.5. Initial oxidation leads to the sulfoxide
which can decompose into a sulfenic acid, which can continue to consume
hydroperoxides in a series of further oxidation steps, leading ultimately to low
molecular weight oxidized sulfur species.
Diesters of thiodipropionic acid are less effective than phosphites at con-
trolling melt viscosity in polymers, but the cascade of chemistry that allows the