Food Lipids: Chemistry, Nutrition, and Biotechnology

ascorbic acid, on the other hand, has been found when the diet also contained an
elevated level of �-tocopherol [223,224]. In another study, Erickson [225] demonstrated
how distribution site can impact effectiveness of ascorbic acid. In that study,
vacuum tumbling was used for the exogenous application of the antioxidant for
intercellular distribution in channel catfish fillets, whereas an ascorbic acid bath was
used to deliver the antioxidant to live channel catfish for absorption and intracellular
distribution in the muscle tissue [226]. Final muscle concentrations of ascorbic acid
with both treatments were twice what they were prior to treatment, but responses
differed. In the case of intercellularly distributed ascorbic acid, the reducing agent
protected membrane phospholipid but accelerated oxidation of triacylglycerols. In
contrast, intracellularly distributed ascorbic acid did not accelerate oxidation of triacylglycerols
but again protected membrane phospholipids. Considerations of compartmentation
as well as the antioxidant polarity and target membrane charge must
therefore be taken into account to develop more effective treatments for enhancement
of tissue stability.
3. Carotenoids
The carotenoids are a group of fat-soluble pigments characterized by a linear, long
chain polyene structure. Besides their roles in pigmentation and vitamin A activity,
carotenoids may have a function similar to that of �-tocopherol, i.e., to protect tissues
from oxidative damage through scavenging of singlet oxygen and scavenging of
peroxyl radicals [178]. In a manner exclusive of hydrogen abstraction, carotenoids
are postulated to scavenge peroxyl radical through addition of the radical to the
conjugated system such that the resulting carbon-centered radical is stabilized by
resonance. When oxygen concentrations are low, a second peroxyl radical is added
to the carbon-centered radical to produce a nonradical polar product. At high oxygen
pressures, however, carotenoids act as prooxidants because the carbon-centered radical
may add oxygen in a reversible reaction, resulting in an unstable chain-carrying
peroxyl radical, which can further degrade to radicals and nonradical polar products
with no net inhibition of oxidation [227]. As to performance of carotenoids in muscle
tissue, the response to supplementation has varied. In postmortem supplementation,
Lee and Lillard [228] observed similar levels of oxidation in cooked control and �carotene-mixed
hamburger patties following refrigerated storage. On the other hand,
Clark et al. [229] reported that dietary canthaxanthin delayed formation of oxidative
products in minced trout flesh during refrigerated storage. Similarly, Bjerking and
Johnsen [230] observed a positive antioxidant effect in rainbow trout fillets. However,
dietary supplementation has not always had a positive effect. Sigurgisladottir et al.
[231] and Maraschiello et al. [232] did not observe any antioxidant effects by dietary
carotenoids in salmon and broiler muscle tissue, respectively. Ruiz et al. [233] contended
that sufficient levels of �-tocopherol must be present to demonstrate an antioxidant
effect by carotenoids. In cases where the proportion of carotenoid/�-tocopherol
is too high, the carotenoid competes with tocopherol for absorption and the
levels of �-tocopherol in the muscle decline. Variability in distribution of the carotenoid
in the muscle tissue [208] could also account for different responses in dietary
supplement studies if sample size is inadequate. As a final note, deposited carotenoids
in muscle have different stabilities during storage (i.e., astaxanthin is more stable
than canthaxanthin [234]), and these stabilities should be considered in supplementation
of muscles to increase oxidative stability of the tissue.
Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.