Page last updated: Tuesday, November 18, 2008
Antioxidants - never out of the news
Who could have failed to see the myriad of front page leaders around the world dedicated to the virtues of resveratrol and procyanidins in red wine (and dark chocolate) following two research articles published in Nature (Corder R, Crozier A et al ‘Red wine procyanidins and vascular

health’ and Baur JA et al ‘Resveratrol improved health and survival of mice on a high calorie diet’). Indeed, the research was the most widespread story reported in the world that day - with journalists apparently elated, in the run up to Christmas, that a little of those ‘naughty’ things in life are not only enjoyable, but positively not bad for you. The publicity has led to a surge of red wine sales in the US to twice their expected growth rate in November. It is important to keep such publicity in proportion as an industry or indeed as consumers. No one should be choosing to drink for ‘medical benefits’ rather than enjoyment and pleasure. Secondly, it is not deemed acceptable for producers to promote or market their products as antioxidant-rich (which can by applied to traditional beers and ciders, even whisky as well as red wine) or as a health drink. In this era when many are seeking a universal panacea, there is no better alternative to the five ‘ingredients’ to a longer and healthier life - namely staying slim, eating a Mediterranean-style diet, exercising for 20 minutes daily, not smoking and drinking in moderation.

Such head lines are important in the sense that they do reinforce the ‘rights’ of moderate drinkers in that alcohol can be included as part of a healthy diet and lifestyle. Some critics have stated that the continuing good news for red wine drinkers will encourage those at risk of a heart attack or a second heart attack to drink more or above daily sensible drinking guidelines and it is worth revisiting Professor Klatsy’s work in this field. In ‘Do people drink more if they develop Coronary Heart Disease (CHD) or know about medical benefits of alcohol’ (AIM Vol 13 No.1 Jan 2004), Klatsky’s subjects were drawn from 63,000 subjects in 1999, drawing on their drinking information supplied between 1978 and 1985. The analysis in 2000, found that 92% of the participants remained abstainers 20 years after first analysis, although 82% of the participants had heard of the medical benefits of alcohol. Of those who had contracted CHD, 18% had become abstainers, the same proportion as in the control, and more had given up smoking. Klatsky’s findings concluded that knowledge of alcohol’s potential beneficial effect did not alter patients drinking habits.

Antioxidants revisited:

Antioxidants include naturally occurring vitamins, phenolic compounds or other complex molecules generated by heat (i.e. cooking) such as elanoidins. Resveratrol, along with quercetin and epicatechin, is one of the main antioxidants found in wine. These phenolic bioflavonoid compounds, a group of chemicals called phytoalexins, are produced by plants in response to fungal infection, ultraviolet light, and various chemical and physical stressors, especially during ripening. Dr Edwin Frankel, of the Davis University of California, has shown that these antioxidants in wine are five times more potent as antioxidants than the benchmark antioxidant, vitamin E.

Scientists previously believed that CYPIBI was a cause of cancer because it is only found in tumours and not in healthy tissue. Researchers now think the enzyme is there to fight cancer and research continues as to how the enzyme and resveratrol work.

Corder and Crozier’s research sheds doubt on the validity of resveratrol as the most important antioxidant, believing its quantities in red wine too insignificant to be valid. They believe procyanidins are more beneficial. during wine making may influence the amount of resveratrol left in the wine after filtration. Various fining agents commonly used by oenologists were tested. Polycar removed 92% of resveratrol. Casein, egg white and alginate also removed some resveratrol whilst gelatin had a variable but relatively little effect. So winemaking techniques, as well as grape variety (red wines contain more resveratrol than white) and growing season (summer rain years produce more resveratrol) play a role as to how much resveratrol there is in a wine. Similar research from Caroline Walker from Brewing Research international on Ciders and beers, has shown that the antioxidant activity in cider can vary from 2,500 to 10, depending on the producer.

Bioavailablity - does size matter? The ease with which we can absorb any compound is called the

bioavailability and this needs to be measured for each food and beverage individually to get an accurate picture of how good a source of antioxidants it is. It has been established that the consumption of two 100ml glasses of red wine a day may increase the phenolic content of the average diet by 40%, but only a weak correlation exists between polyphenolic content and antioxidant activity.

Ferulic acid, in contrast is highly absorbable. Although it has not been completely established, it would be expected that the larger bulky antioxidants are likely to stay in the gut rather than to get absorbed.

Important facts:

Antioxidant activity in unfermented grape juice is lower than in the finished wine - antioxidant activity increases during fermentation and maturation. Antioxidant levels will depend on the processing, filtering for example, as well as on the variety, vintage, altitude and soil. Original research in Australia by Professor Geoff Skurray at The University of Western Sydney has shown that different wine filtration techniques.

How and where are these molecules absorbed into the bloodstream?

A group in Italy has shown that antioxidants are transported directly through the stomach wall, which has cells in it containing a transport protein called Bilitranslocase. This molecule is also used by the body to get the waste product bilirubin out of the bloodstream into the liver, where it is metabolised for excretion: it is the product of the decay (natural) of red bloodcells. Bilirubin causes neonatal jaundice, and is responsible for the yellowish colour around bruises.

Bilitranslocase also interacts with anthocyanins, and transport them first into the bloodstream directly from the stomach, and then even into the liver and into brain tissue. While the amount absorbed is small, it gets to the named organs very rapidly.

Furthermore, research suggests that once absorbed, antioxidants are often metabolised into other forms which may have different biological activity. For example, much of the resveratrol is modified in the liver by coupling to glucuronic acid. Therefore establishing the absorption and further metabolism of antioxidants is a key factor in establishing their biological effects.

We have also learnt that ethanol has a pro-oxidative effect on plasma lipids.

Hence the usefulness or bioavailability of the antioxidants available in alcoholic beverages is not yet fully established. However the importance of antioxidants themselves in vascodilation, fighting cancer and dementia are established and further research as to absorption by the human body is needed.

The full article and references are availabel on the Corporate Subscribers Area

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