By Jane Byrne , 22-Feb-2010
“I'm strong to the finish when I eats me spinach,” said Popeye the sailor man, and he could have snatched Olive Oyl from the clutches of Bluto with even more ferocity if he had eaten his broccoli, tomatoes or onions according to an Australian/New Zealand project focused on super vegetables.
In the continuing Nutraingredients series on antioxidants, we look at these rivals to super fruits in terms of their antioxidant potential.
Carolyn Lister, research leader at the New Zealand Institute for Plant & Food Research told this publication that while fruit has tended to attract the greatest attention and the ‘super’ label, there is a body of clinical research underlining the significant health benefits of vegetables in both raw and cooked form, with broccoli along with the other brassicas, tomatoes, onions and other alliums proving to be the vegetables with the strongest scientific evidence behind them.
“This evidence varies from in vitro studies through to human feeding studies.
Although there is considerable variation in the results of different studies (at least in part due to the design of trials - these have often been done using a pharmaceutical type approach and this is not always relevant for design of trials with food), looking at the summation of results, there is quite strong evidence for benefits to human health of a number of vegetables,” she claims.
Lister is one of the key scientists involved with the Vital Vegetables programme, a research initiative between the Australian and New Zealand horticultural industries set up to develop vegetables with increased health benefits, using traditional breeding techniques.
Broccoli and beyond
In 2009, the joint research programme launched a variety of broccoli, Booster Broccoli, on the Australian market that is said to have 40 per cent more active antioxidants than regular broccoli varieties.
Lister explained that this variety has guaranteed levels of glucosinolates/sulforaphane, and is the first of a range of vegetables where the team measures and monitors the levels of active components within.
And she said hundreds of scientific papers, based on epidemiological data supported by experimental studies with cell and animal models and more recently small-scale human intervention trials, have been published detailing the effects of sulforaphane on cardiovascular disease, certain forms of cancer, diabetes, as well as degenerative diseases such as Alzheimer’s and Parkinson’s disease.
Furthermore, continued Lister, the multiple actions of sulforaphane in humans have been widely studied since 1992 when Professor Paul Talalay and associates at Johns Hopkins University discovered its action as an inducer of detoxifying enzyme systems.
“Although broccoli contains a diversity of nutrients and phytonutrients, such as flavonoids and carotenoids, the components that uniquely set broccoli and other crucifers apart from other vegetables are the glucosinolates.
In particular glucoraphanin that is then converted to sulforaphane. Sulforaphane has attracted the most attention from a research perspective in terms of its health benefits. Although not a radical scavenging antioxidant it acts as an indirect antioxidant,” she added.
Tomatoes and onions
Lycopene, the bright red carotenoid pigment, is present in tomatoes in reasonable quantities but available in relatively few other foods, continued Lister.
The health benefits of tomatoes/lycopene have been the subject of a number of scientific reviews but the most intensively investigated, she maintains, is its cancer preventative ability: “The results of several prospective cohort studies suggest that lycopene-rich diets are associated with significant reductions in the risk of prostate cancer, particularly more aggressive forms.”
Lister explained that onions contain sulfur compounds and flavonoids and that their antioxidant potency and anti-cancer properties are being supported by research studies.
She also highlights the antioxidant benefits of capsicums with their high levels of vitamins A, C and E as well as sweetcorn, which she said contains lutein and zeaxathin to benefit eye health.
One vegetable that often gets overlooked is the potato, said Lister, which is a good contributor of vitamin C depending on how it is cooked. “Red and purple skinned may offer greater benefits than standard potatoes and we have developed new cultivars on this basis,” she added.
She said there are a range of less mainstream vegetables that may contain higher levels of phytochemicals and that could be exploited as super vegetables such as watercress.
But Professor Jeya Henry, head of the Functional Food Centre at Oxford Brookes University in the UK England, claims that consumer perception is currently preventing the advent of ‘superveg', and he said regulators and scientists need to boost clinical research and marketing to entice consumers and processors to make greater use of them.
And Stewart Rose, vice president of the US non-profit organization, Vegetarians of Washington argues that there are currently few crops that have consistent scientific backing for using health claims besides products like broccoli – the knock on effect, he argues, is a lack of innovation in regards to super vegetaables on the part of food manufacturers.
He said that while a single study praising the potential benefits of a vegetable had shown demand balloon positively, similar negative research could hit sales just as quickly, pointing to falls in the popularity of carrots in the US following mixed research into the potential benefits and dangers of the vitamin A precursor beta-carotene within carrots.
But despite the possible difficulties, he said that there was growing interest in the US for the possibility of ‘superveg’, particularly in the aging baby boomer demographic that dominates demand in the US, meaning further promotion and research was viable.