Page last updated: Tuesday, November 18, 2008
Oxidation, free radicals and antioxidants in wines
by D.G.Hewitt and G.J Troup
A neutral atom consits of a positively charged nucleus surrounded by acloud of negatively charged electrons; the total charge on the electrons is equal to that on the nucleus. If an electron is removed from the atom, the atom is said to have been oxidised. Of course, we may be able to continue to remove electrons from the atom, and each step is a further oxidation.

Consider the copper (Cu) oxide, CuO. We may write that Cu2+ O2-, to illustrate that two electrons have been removed from the Cu, and given to the O to form the oxide. It was this kind of process that eventually gave the name oxidation to electron removal from an atom or a molecule. The atom or molecule receiving the electron is said to have been reduced. Note that the removal of an electron from a charged atom which has been reduced, e.g. C1-, is also called oxidation.

A free radical is an electron that is not magnetically paired up with another electron. Electrons are not only charged, they are magnetic as well because they possess a spin, an angular momentum. Two identical bar magnets will attract one another very strongly if they are next to one another and pointing in opposite directions: the same is true for two electrons with their magnetic moments (spins) opposed. A free radical is usually attached to an atom or molecule, from which it will take its name. The simplest free radical to consider is the neutral hydrogen atom H. The electron of thisatom is not paired magnetically with another electron, but suppose it comes close to another H atom wtih an electron having the opposite spin direction.

The resultant attractive force between the electron magnetic moment helps form the hydrogen molecule H2. So this property of a free radical can make it a very strong molecular oxidation processes.

There are myriads of chemical reactions going on in our bodies all the time, because we are alive, and need oxygen and food and water to keep us so. Many of theses reactions will be oxidation reactions, some mediated by a free radical, and therefore good for us. But things can go wrong, as we shall see. Consider the uptake of O by the haemoglobin in the blood. This is clearly vital for our survival, and an oxidation reaction. But we hyperoxygenate, by breathing fast and deep without excercising, the physiological results for us can not only be unpleasant, but possibly dangerous.

Now let us think about cholesterol. It is necessary for us, otherwise the liver would not manufacture it. There are two kinds of cholesterol, the LDL and HDL. LDL means low density lipid (lipid is fat) and HDL means high density lipid. The oxidation of the LDL leads to a product that clogs arterial walls, and leads to heart disease and atherosclerosis. The oxidation of LDL is mediated by the so called superoxide (anion) radical, O2' , where the is used to indicate that it is a free radical. Anion, meaning negatively charged, is put in brackets because it is very often omitted in the discussion of this radical. The charge means that this radical is very reactive.

So how does such a radical occur in our bodies? One way is through the 4 - step change of the O2 molecule into water. Apart from the SOA radical, in this process we have the hydroxyl radical, which is clearly very reactive and the hrdrogenperoxide molecule, which is notparticularly stable. Free radical vary considerably in their reactivity,some are very vigerous in donation (SOA radical) or acceptance (hydroxylradical) of electrons. this means that they can interact destructively withmany other chemicals including those within us. Others, such as some of the radicals found in wine and other foods, are essentially permanently stable,and provide a sink for reactive electrons. When a molecule such as a tannin from wine meets the very reactive SOA radical for example, the SOA is converted into the more stable (less reactive) hydrogen peroxide, and the tannin is converted into one of the very stable (unreactive) free radicals. In this way the bad radicals are converted into good (harmless) radicals, and the chemicals necessaryfor our bodies are protected. Such a molecule is called a radical scavanger or an antioxidant.

The preferred kind of antioxidant is one which removes the unpaired electron, and stablisises it by delocalising it - that is spreading the probablilty of finding it over a large area of the molecule and thus reducing the probalilty of finding at any particular point.

Antioxidants in wine.

First red wine, made from red grapes. The great storehouse of antioxidants in red grapes are the skins, which give the wine its colour,and the seeds, which give the wine its astringent taste. The antioxidants in both cases are what are called polyphenols. A simple phenol consists of a hexagonal ring - shaped molecule, which has at least one hyroxyl group (OH) attached to a corner of the ring, and some other group, denoted by R, say, attached to another corner (Fig 2). Even this simple phenolic can act as a radical - stabilising antioxidant, because the unpaired electron will partake of some of the electronic motion around the ring, and so delocalised. A polypnenol may have two or more phenolic rings joined together by some means (Fig 3), and of course these molecules can bond together to make larger molecules called oligomers if only a few of them are involved and polymers if a lot of them are involved.We have chosen to show a particular shape of molecule which is common to both the anthocyanins, which do the colouring, and the flavanoids and tannins, whichgive the astringent taste. In general red wines are left to ferment on the skins and seeds after the grapes are pressed. They can also be treated with oak in many ways: barrels, planks,chips. the oak contains compounds of gallic acid, also a phenol, which can react with the other phenols in various ways. It is not necessary to treat red wines with oak for them to contain antioxidants.

Now let us consider white wine which can be made from red grapes as well aswhite ones, by immediately seperating the juice from the skins and seedsafter pressing. It is quite clear that such a wine cannot contain as many antioxidant molecules as a wine left to ferment on the skins and seeds. We can, of course, leave the juice from white grapes to ferment on the skins and seeds, but this willl not produce a wine having as many antioxidant molecules as a red wine similarly treated. Nor will the oak treatment of such a wine give an antioxidant content as greate as that of a red wine.

There are at least two works which report that white wines used in experiments on the antioxidant action of wine in the blood had a pro-oxidant interaction. Unfortunately, the tannin content of the wines was not measured in each case, but we can confidently say that zero tannin concentration will mean little, if any , antioxidant action. Indeed, there may well be a threshold concentration for the antioxidant action to begin.

Recently, some researchers reported that they had to invent their own white wine in order to observe readily the antioxidant action: they did this by adding alcohol to the wine being fermented with skins and seeds. The extra alcohol leaches more tannins from the seeds, but results in a much sweeter wine. Such a procedure for a table wine is illegal in many countries! So, to be safe, drink white wine for pleasure, and red wine for your health as well. Those allergic to red wines should only drink white wines exposed to skin, seeds, oak, or even supplement their diet with red grapeseed extrectsuch as Pycnogenol (R) orActi-Vin. .

The effect of white wine with a nearly zero antioxidant (tannin)concentration agrees with the work of two independent French researchers on two different kinds of laboratory animals. First, 10% alcohol red wine was introduced into their diet, which, it was found, they could sustain for months without serious damage as compared to the control groups. Then, the wine was distilled to make a spirit, "eau de vie", which was then diluted to 10% alcohol, and included in the diet. Some of the animals became seriously ill. Finally, very pure alcohol mixed with distilled water, to 10% dilution, added to the diet. This had serious consequences for a much larger proportion of the animals.

Where red wine can help us

The disease or health conditions where red wine can help us are those which are brought about by the action of bad free radicals - for example cardiovascular and cerebrovascular disease such as clogging of the arteries, heart attack, stroke and dementia caused by insufficient blood supply to the brain (ischeamic dementia). Free radicals are also known to cause inflammatory conditions and tissue damage, so red wine will act as protection against these. It is thought that the unexpected effect of wine in at least delaying the onset of Alzhelmers disease is due to its reduction of the inflammation associated with the build up of amyloid plaques which cause the disease in the brain. The combination with moderate (red) wine consumption of appropriate doses of Chromium polynicotinate or picolinate, together with appropriate diet and exercise, can help to get rid of Syndrome X - the initiation of late onset diabetes. Cr (4+) is an antioxidant which works in synergy with the wine antioxidants.

Further observations

What about grape juice without the alcohol? Sorry, grape juice contains 6x as much sugar as table wine, and this clearly is not good. Besides, the alcohol and the polyphenols work together to stregthen the heart, and prevent arterial clogging. What about the antioxidants in beer and stouts? Again sorry. they are simply not as efficeint as those in wines: and yes, the experimental work has been done. What about grapeseed extracts, such as Pycnogenol or Grapeseed 2000? Well, these are certainly better than grape juice, because they lack the sugar, but the alcohol protection is lost.

Eat a Mediterranian diet, rich in fruits and vegetables, low in red meat, rich in good breads and pastas, and using extra virgin oil (which contains further phenolic antioxidants) and wash the meal down slowly with (red) wine in moderation, with the family and freinds. The sheer enjoyment and the relaxation is part of the medicine! Oh ... and dont forget the excercise, say 30 mins, brisk walking 5 days a week!

D.G.Hewitt and G.J.Troup,Chemistry Department and School of Physics and Materials Engineering Monash University, Clayton, Victoria, Australia.

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