Page 114 - Academic Press Encyclopedia of Physical Science and Technology 3rd BioChemistry

P1: GTQ/GUB P2: GSS/GJP QC: FYD Final Pages
Encyclopedia of Physical Science and Technology EN010B-472 July 16, 2001 15:41

342 Natural Antioxidants In Foods

Two ascorbate peroxidase isozymes have been described of how these endogenous antioxidants protect foods from
that differ in molecular weight (57,000 versus 34,000), oxidation is still in its infancy. In addition, how factors
substrate specificity, pH optimum, and stability. that can alter the activity of endogenous food antioxidants
(e.g., heat processing, irradiation, and genetic selection
of foods high in antioxidants) is still poorly understood.
D. Glutathione Peroxidase
Finally, research is continuing to show that natural food
Many foods also contain glutathione peroxidase. Glu- antioxidants in the diet are very important in the modu-
tathione peroxidase differs from catalase in that it de- lation of disease. Thus, finding mechanisms to increase
composes both lipid and hydrogen peroxides. GSH-Px natural food antioxidants may be beneficial to both health
is a selenium-containing enzyme that catalyzes hydrogen and food quality.
or lipid (LOOH) peroxide reduction using reduced glu-
tathione (GSH):
H 2 O 2 + 2GSH—2H 2 O + GSSG SEE ALSO THE FOLLOWING ARTICLES
or, FOOD COLORS • HYDROGEN BOND • LIPOPROTEIN/

LOOH + 2GSH—LOH + H 2 O + GSSG, CHOLESTEROL METABOLISM
where GSSG is oxidized glutathione and LOH is a fatty
acid alcohol. Two types of GSH-Px exist in biological tis- BIBLIOGRAPHY
sues, of which one shows high specificity for phospholipid
hydroperoxides.
Buettner, G. R. (1993). “The pecking order of free radicals and an-
tioxidants: Lipid peroxidation, α-tocopherol, and ascorbate,” Arch.
Biochem. Biophys. 300, 535–543.
E. Antioxidant Enzymes in Foods
Decker, E. A. (1998). “Strategies for manipulating the prooxida-
Antioxidant enzyme activity in foods can be altered in tive/antioxidative balance of foods to mazimixe oxidative stability,”
Trends Food Sci. Technol. 9, 241–248.
raw materials and finished products. Antioxidant enzymes
Decker, E. A., and Clarkson, P. (2000). “Dietary sources and bioavail-
differ in different genetic strains and at different stages ability of essential and nonessential antioxidants,” In: Exercise and
of development in plant foods. Heat processing and food Oxygen Toxicity (C.K. Sen, L. Packer, and O. Hanninen, eds.). pp.
additives (e.g., salt and acids) can inhibit or inactivate 323–358. Elsevier Science, Amsterdam.
antioxidant enzyme activity. Dietary supplementation of Frankel, E. N. (1996). “Antioxidants in lipid foods and their impact on
food quality,” Food Chem. 57, 51–55.
selenium can be used to increase the glutathione peroxi-
Graf, E., and Eaton, J. W. (1990). “Antioxidant functions of phytic acid,”
dase activity of animal tissues. These factors suggests that Free Rad. Biol. Med. 8, 61–69.
technologies could be developed to increase natural levels Halliwell, B. (1999). “Establishing the significance and optimal intake of
of antioxidant enzymes in raw materials and/or minimize dietary antioxidants: The biomarker concept,” Nutr. Rev. 57, 104–113.
their loss of activity during food processing operations. Halliwell, B., Murcia, M. A., Chirico, S., Aruoma, O. I. (1995). “Free
radicals and antioxidants in foods and in vivo: What they do and how
they work,” Crit. Rev. Food Sci. Nutr. 35, 7–20.
Krinsky, N. I. (1992). “Mechanism of action of biological antioxidants,”
CONCLUSION Proc. Soc. Exp. Biol. Med. 200, 248–254.
Liebler, D. C. (1993). “The role of metabolism in the antioxidant function
The biological tissues from which foods originate con- of vitamin E,” Crit. Rev. Toxicol. 23, 147–169.
Liebler, D. C. (1992). “Antioxidant reactions of carotenoids,” Ann. N Y
tain multicomponent antioxidant systems that include
Acad. Sci. 691, 20–30.
free radical scavengers, metal chelators, singlet oxygen Nawar, W. W. (1996). “Lipids,” In: Food Chemistry (O. Fennema, ed.),
quenchers, and antioxidant enzymes. Our understanding 3rd edition, pp. 225–319. Marcel Dekker, New York.