Page 195 - Natural Antioxidants, Applications in Foods of Animal Origin

174 Natural Antioxidants: Applications in Foods of Animal Origin
VetBooks.ir 5.3.1 PLANT SOURCES

5.3.1.1 α-TOCOPHEROL (VIT. E)

It is a widely studied antioxidant and has the ability to function in biological
systems. Free radicals are neutralized by tocopherol before lipid oxidation
propagates among highly unsaturated fatty acids in cellular and subcel-
lular membranes. The chromanol ring of α-tocopherol is located among the
polar head groups of the phospholipids, and the phytol side chain interacts
with the unsaturated fatty acyl chains of the phospholipids through van-der-
Waals interactions in the interior of the membrane. This specific localiza-
tion of α-tocopherol in the membrane and the molecule’s lateral mobility
allow it to function very efficiently to protect highly oxidizable PUFA from
per-oxidation by ROS produced by adjacent membrane bound enzymes. A
logical hypothesis is that tocopherol quenches free radicals originating from
lipid oxidation and in-turn protects oxymyoglobin oxidation. It inhibits free
radical oxidation by reacting with peroxyl radicals to stop chain propagation
and with alkoxyl radicals to inhibit the decomposition of the hydroperoxides
and decrease the formation of aldehydes.
Various attempts have been made to reduce pigment and lipid oxidation
in meats by endogenous and exogenous vit. E treatments. Dietary supple-
mentation of vit. E at 2500 mg for 40 days resulted in a 7–10 day exten-
sion of color, shelf life of meat steaks (Taylor et al., 1994). It has also been
reported that animal fed a diet containing 75 or 1000 mg vit. E had higher
concentration of vit. E in meat and lower discoloration. High concentrations
of vit. E have been shown to exert a pro-oxidant effect (Mahoney & Graf,
1986). Post-mortem addition of vit. E was less effective in retarding the
oxidation of pigment and lipid than endogenous one. Thus, dietary vit. E
supplementation would be a safer and more effective method for retarding
pigment and lipid oxidation.
Vit. E had been reported to be effective in improving shelf life of poultry
meat and meat products through delay in oxidation. But the efficacy of oxida-
tive stability of poultry meat is related to tissue concentration of tocopherol.
As the level of vit. E in diet increases there is concomitant increase in its
concentration in tissues. High level of vit. E in poultry meat not only improves
the oxidative stability but also prevents excessive drip loss, as it is believed
that α-tocopherol reduces leakage of sarcoplasmic components from muscle
cells by maintaining the integrity of cellular membranes and thereby reduces
drip (Goni et al., 2007). The sensory quality of meat assessed from scoring
of aroma, flavor, taste, etc. is reported to be improved by adding vit. E in