The findings provide scientific backing for previous studies suggesting that higher intake of fruit and vegetables may lower the risk of developing the disease.
Due to present the research at the British Pharmaceutical Conference in Manchester, the scientists from King's College London have found that compounds in each of these fruit and vegetables inhibit acetylcholinesterase, the enzyme responsible for the breakdown of the neurotransmitter acetylcholine.
This is also the target of common Alzheimer's drugs and although it has been previously suggested that some vegetables might have this activity too, no detailed investigation has ever been carried out, claim the UK team.
Of each of the fruit and vegetables studied, broccoli was found to have the most potent activity and in further tests, the researchers showed that glucosinolates, a group of compounds found throughout the cabbage family, were likely to be responsible for this action.
Professor Peter Houghton, from King's College London, noted that this is "the first report that glucosinolates have acetylcholinesterase inhibitory properties".
They have previously been studied for their anti-cancer activity.
He cautioned that it has not yet been proven that eating broccoli would have a beneficial effect on Alzheimer's disease.
However he added: "But the long-term effects of regularly consuming these compounds in vegetables belonging to the Brassicaceae (cabbage family) might certainly be beneficial in reducing a decline in acetylcholine levels in the central nervous system."
Potatoes, especially green ones that tend to be avoided by consumers, also have the potential to fight mental decline as glycoalkaloids like solanine have a similar action to glucosinolates.
Their acetylcholinesterase inhibitory properties have previously been shown by other researchers.
"It would be nice to do more population-based studies to confirm these results," Professor Houghton told NutraIngredients.com.
There are nearly 18 million people with dementia in the world and the most common cause of this dementia is Alzheimer's disease. By 2025 this figure will rise to 34 million, with 71 per cent of these likely to live in developing countries, making the need for prevention of the uncurable disease crucial.
Ageing populations and increasing overweight are driving incidence of the disease upwards.