Natural antioxidants as food and beverage ingredients - Natural Food Additives, Ingredients and Flavourings - page 114

dietary factor essential for reproduction' (Evans and Bishop 1922). The family of
tocopherols consists of four different congeners known as α -tocopherol (vitamin
E), β -tocopherol, δ -tocopherol and γ -tocopherol (Fig. 5.9). They are relatively
stable and very effective (to varying degrees, based on the congener) lipid-soluble
antioxidants available on a large scale. They are commonly used in fats, oils, meat
and baked goods.
Due to their liposolubility, tocopherols are used for vegetable oils, where they
occur naturally, and animal fats. δ -Tocopherol seems to be the most stable
followed by β -tocopherol, γ -tocopherol and fi nally α -tocopherol. The potency
trend is slightly different, with δ -tocopherol and γ -tocopherol appearing to be the
most potent (in lard at 100°C) while α -tocopherol is almost inactive (Sims and
Foioriti 1991). As in most of the phenolic antioxidants we have considered, the
main mode of action for tocopherols is radical scavenging of both peroxyl and
alkoxyl radicals (Frankel 1996). It is also reported that tocopherols are good
singlet oxygen quenchers through a charge transfer mechanism (Kim and Min
2008) (Fig. 5.10).
There are reports of prooxidant activity of tocopherols in some food systems
and food models (Frankel 1996). The mode of action of chromanols (the chemical
class of tocopherols) is reported to vary signifi cantly as the physico-chemical
parameters of the system change (Kamal-Eldin and Appleqvist 1996), which
could help explain the variable results observed (antioxidant vs. prooxidant).
Tocopherols extend the shelf life of vegetable oils and retard lipid oxidation
(Lampi and Kamal-Eldin 1998). They are very effective in inhibiting
polymerization in sunfl ower, rapeseed and high-oleic sunfl ower frying oils (Lampi
et al. 1999). Additionally, they are effective in butterfat applications (Dougherty
1993) and useful when added directly to both raw and cooked meat. Antioxidative
effects have also been seen in meat produced through tocopherol feed
supplementation (Lavelle et al. 1995; Formanek et al. 2001). Tocopherols are also
effective in slowing lipid oxidation in fi sh oil-enriched energy bars if prooxidative
￿ ￿ ￿ ￿ ￿
Fig. 5.9 Tocopherols.