Key Points:

If you think a glass of breakfast orange juice is the best way to start the day, think again.

Grape juice could be more beneficial.

Scientists have carried out the first scientific analysis of fruit juices to measure their anti-oxidant activity - the anti-ageing compounds that protect against heart disease and other chronic conditions.

Top of the league is purple grape juice followed by apple juice and cranberry juice, according to the study by researchers at the University of Glasgow.

Orange juice, the most popular fruit juice, comes way down the league.

It contains fewer polyphenols than the other juices tested, which are strong anti-oxidants.

Alan Crozier, professor of Plant Biochemistry and Human Nutrition who led the study, said: "Not all fruit juices are the same. The findings reveal that the variety of phenolic compounds and antioxidant capacity of the individual juices varied markedly."

"Purple grape juice made with Concord grapes contains the highest and broadest range of polyphenols as well as having the highest antioxidant capacity. Other high-ranking products include cloudy apple juice and cranberry juice drink."

The research was funded by the National Grape Co-operative, a consortium of farmers in the US owned by Welch's, makers of Concord purple grape juice.

It is published in the Journal of Agriculture and Food Chemistry.

The finding comes in the wake of research by US scientists which showed an association between long term fruit juice consumption and a reduced risk of Alzheimer's disease.

Researchers who followed almost 2,000 volunteers for up to ten years found the risk of Alzheimer's was 76 per cent lower for those who drank juices more than three times a week compared with those who drank them less than once a week.

The Glasgow study suggests these protective effects may be strengthened by consumption of a combination of juices with a high concentration and broad range of polyphenolic antioxidants.

Anti-oxidants are compounds such as vitamin C found in fruits and vegetables which are believed to play a key role by protecting the body from the damaging effects of free radicals, the products of metabolism.

By quenching free radicals they help to maintain oxidative balance and prevent the development of diseases including cancer and heart disease.

Professor Crozier said: "Supplementing a healthy diet with a regular intake of a variety of fruit juices such as purple grape juice, grapefruit juice, cloudy apple juice and cranberry juice, will increase the consumer's intake of phenolic antioxidants."

He added: "The message is to mix these juices during the week. That way you will get all the compounds with anti-oxidant activity. If you drink only one juice you risk missing out on the compounds in the others."

He said Welch's had asked his research team to measure the anti-oxidant activity in 13 of the most popular fruit juices in Britain.

"The paper we have published is as we wrote it. If Welch's had written it they would have said drink only Concord grape juice."

As well as purple grape juice, the fruit juices examined in the study included cloudy apple, pomegranate, cranberry, grapefruit, clear apple, pineapple, orange, tomato, red grape and white grape.

The findings also revealed the number and level of antioxidant phenolic compounds in purple grape juice equates with those found in a Beaujolais red wine.