DANGEROUS GAS
A simple experiment in antioxidation. Lemon juice can prevent the browning of a cut
apple, thanks to the antioxidant action of vitamin C.
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The potency of oxygen and the need for
antioxidants One of the most potent and dangerous gases on earth is oxygen.
Surprised? Surely oxygen is the stuff of life; it is other gases like nitrogen, carbon
dioxide, chlorine that are life-threatening. But because oxygen is indeed the substance
that powers all animals we are blind to its destructive power. The atmospheric chemist
James Lovelock has said that if the oxygen content of the atmosphere were a little higher,
say 25% (instead of its actual level of 20%) the earth would be consumed in an enormous
uncontrollable forest fire. On a more mundane level, rusting is a graphic demonstration of
what oxygen does to iron.
Living systems are protected against oxidation so long as they are alive. But all
foodstuffs are vulnerable to oxidation. The most familiar examples are the browning of
apples or potatoes exposed to the air. The well-known remedy for this, a drop of lemon
juice, demonstrates the principle of antioxidation. Lemon juice contains vitamin C (E300),
one of the most potent antioxidants.
Atmospheric oxygen is not the only oxidizing agent. It is combined in the form of
oxides and peroxides in atmospheric pollution, cigarette smoke and in some normal bodily
processes. Oxidation is dangerous to living systems in many ways. It can cause breaks in
DNA (and hence the risk of cancers), it can oxidise polyunsaturated fatty acids, and thus
contribute towards heart disease and strokes; and it can damage the proteins that make up
much of our issue. The proteins in the eye are particularly vulnerable because light also
assists the oxidation process.
There is increasing awareness that protection against the ravages of oxygen can have a
very beneficial effect on health and a great deal of research is currently underway. There
is no doubt that increasing the intake of antioxidants has a preventative effect against
both cancer and heart disease (oxidation of lipids is one factor in the development of
heart disease), but it is not clear which antioxidants are the most effective.
Besides all their other advantages, antioxidants confer huge economic and environmental
benefits in preventing wastage of food, a huge problem in the food production of less
developed societies.
Vegetables contain several antioxidants besides vitamins C and E, especially the
flavonoids, of which quercetin in onions and apples and epigallocatechin in tea are
typical examples. In one study, increasing vegetable intake by at least 400 g per day
resulted in a 42% reduction in the risk of coronary heart disease. Flavonoids have become
the subject of intensive research in recent years for their strong antioxidant properties.
Oxidative reaction are also implicated in the development of diabetes and Vitamin E has
been found to have a preventative role here too.
Antioxidants thus have wide-ranging life-protective properties. Vitamins C and E (E306)
are the two antioxidants present in living creatures, including ourselves, which fulfill
the antioxidant role, and which are also widely used as supplementary additives. These are
amongst the safest chemicals known: a recent survey concluded 'vitamin C inhibits the
formation of carcinogenic nitrosamines, stimulates the immune system, protects against
chromosome breakage, regenerates vitamin E as part of the antioxidant defence system'.
The most common synthetic antioxidants are butylated hydroxyanisole (E320) and
butylated hydroxytoluene (BHT; E321). BHT has been controversial; it has produced adverse
reactions in dogs but like all antioxidants it is anticarcinogenic; a good example of the
complexity of the chemistry of life, in which things are rarely either/or. The Joint
FAO/WHO Expert Committee on Food Additives have recently considered the Acceptable Daily
Intakes (ADIs) of BHA and BHT and set them at 0-0.5 mg/kg body weight for BHA and 0-0.3
mg/kg body weight for BHT.
1 D. Kromhout, 'Are Antioxidants Effective in Primary
prevention of Coronary heart Disease', in Natural Antioxidants and Anticarcinogens in
Nutrition, Health, and Disease, ed J. T. Kumpulainen, and J. T. Salonen, Royal
Society of Chemistry, Special Publication No 240, 1999, pp20-26
2 P. C. H. Hollman, M. G. Katan, 'Analysis of health effects
of flavonoids', Food Chemistry, 57, (1), pp43-46, 1999
3 P. Knecht and A. Reunanen, 'Antioxidants and Diabetes
Mellitius', in Natural Antioxidants and Anticarcinogens in Nutrition, Health, and
Disease, ed J. T. Kumpulainen, and J. T. Salonen, Royal Society of Chemistry, Special
Publication No 240, 1999, pp20-26
4 A. T. Diplock, J.-L. Charleux, G. Crozier-Willi et al,
'Functional food science and defence against reactive oxidative species', British Journal
of Nutrition, Volume 80 Supplement 1, August 1998
5 Safety evaluations of certain food additives', WHO Food
Additives Series: 42, WHO, 1999. |
