Genetically-modified (GM) purple tomatoes with high levels of health-giving antioxidants - developed by Norwich scientists - could be available in the USA from next spring.

Prof Cathie Martin and her team at the John Innes Centre has been researching tomatoes since 2008 as part of a long-term project to improve human health and diets.

She told members of Stalham Farmers’ Club that several GM purple tomato varieties were in the final stages of lengthy and exhaustive regulatory reviews in the United States.

If approved, it was possible that seeds of the purple tomato varieties might be available to gardeners and growers in the American market from the early spring, she said.

Prof Martin, who recently won the international Rank Prize for Nutrition, said the purple tomatoes developed at the John Innes Centre were bred using gene technology to contain much higher levels of anthocyanins – antioxidant nutrients – which can have significant benefits in human diets.

While current GM regulations prevent them from being grown commercially in Britain, she explained there might be an opportunity to grow these varieties here when the regulatory reviews had been completed.

But the first stage was receiving approval in the United States, she said.

Prof Martin said society faced serious challenges caused by a combination of poor diet and consuming too much of the wrong type of foods – hence rising levels of obesity and diabetes.

In addition, typical consumer expenditure on food has fallen significantly in the past half century as a percentage of household spending. “We have to improve our diet,” she argued.

And by eating smarter, there would be significant other benefits. In a major study of more than 300,000 adult deaths from cancers, a lack of fruit and vegetables was the second biggest factor of deaths in men after tobacco in men but it was the fifth in women.

Prof Martin said it was now recognised that including more fresh fruit in the daily diet - for example 70g of blackberries, three purple peppers, or even just two purple tomatoes - could deliver a proportion of the suggested 125mg daily antioxidant nutrients.