Food Lipids: Chemistry, Nutrition, and Biotechnology

flavonols, flavanols, and anthocyanins. Phenolic acids, structurally related to flavonoids,
serve as precursors of flavonoid biosynthesis. Phenolic acids include hydroxycinnamic
(caffeic, p-coumaric, ferulic, and sinapic acids), hydroxycoumarin (scopoletin),
and hydroxybenzoic acids (4-hydroxybenzoic, ellagic, gallic, gentisic,
protcatechuic, salicylic, and vanillic acids). The effectiveness of flavonoids and phenolic
acids in retarding lipid oxidation in foods appears to be related not only to
their chelating capacity but to their ability to act as free radical acceptors. However,
economic and regulatory hurdles prevent the use of the purified forms of these phenolics;
consequently, plant extracts are often examined for their antioxidant potential.
Examples of these types of antioxidant studies are as follows: ground green tea or
commercial tea extracts in a fish meat model system [258]; ground pepper in ground
pork [259]; onions in cook-chill chicken [260]; dried spices or the ethanol extract
of those spices in cooked minced meat patties [261]; aloe vera, fenugreek, ginseng,
mustard, rosemary, sage, and tea catechins in pork patties [262]; rosemary, tea, or
coffee extracts in dehydrated chicken meat [263]; galangal (a rhizome closely related
to ginger) in minced beef [264]; and potato peels, fenugreek seeks, and ginger rhizomes
in ground beef patties [265]. In membrane model system studies, antioxidant
efficiency of flavonoids has been found to be dependent not only on their redox
properties but also on their ability to interact with biomembranes [212]. Hence,
similar to tocopherol, dietary supplementation (as opposed to exogenous application
of these flavonoids) may prove to be more effective. Tea catechins supplemented at
a level of 200 mg/kg chicken feed were equally effective in antioxidant potential as
�-tocopherol at the same level for up to 3 months of frozen storage [267].
7. Antioxidant Enzymes
Superoxide dismutase, catalase, and glutathione peroxidase are enzymes present in
muscle tissues that may be classified as preventive antioxidants. Superoxide dismutase
converts superoxide anion to hydrogen peroxide; catalase converts the hydrogen
peroxide to water and oxygen; and glutathione peroxidase converts hydroperoxides
to alcohols, thereby eliminating their potential decomposition by Fe 2� .
Comparison of these enzyme activities with the metabolic activities in different
fish species suggests that levels of glutathione peroxidase and superoxide dismutase
reflect the degree of oxidative activity in the tissue [268]. Similarly, antioxidant
enzyme activity was higher in the oxidative sartorius muscle of turkey than in the
glycolytic pectoralis major muscle [269]. Nutritional status of the animal prior to
slaughter may also play an important role in dictating the enzyme levels in the
flesh [270,271]. For example, Maraschiello et al. [272] found that glutathione peroxidase
activity in chicken thighs decreased as the level of �-tocopherol in the diet
increased. In contrast, homeostatic compensation did not occur for glutathione peroxidase
activity in turkey muscles upon vitamin E supplementation [269]. Moreover,
addition of dietary selenium was considered to be very effective in maintaining
glutathione peroxidase activities in chicken muscle tissue during storage [273].
Addition of antioxidant enzymes to raw and cooked meats, on the other hand,
produced only low or moderate inhibition of oxidative activity [274,275]. Such
limited usefulness may be due to the susceptibility of these enzymes to inactivation
by active oxygen species [276,277].
Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.