Sustainable fruit shows marked rise in antioxidants

Are organic foods really better for us? The debate continues this week with new findings from food scientists in the US that suggest fruits and vegetables grown organically have higher levels of antioxidants than conventionally grown foods thanks to the plants' natural defence system.

Science remains undecided on whether organic foods are of greater benefit to our bodies than conventional foods. But following her research on the amount of antioxidants found in corn, strawberries and a type of blackberry called a marionberry, Alyson Mitchell, a food scientist at the University of California in the US, claims that the results weigh heavily in organic's favour.

Her research suggests that pesticides and herbicides actually thwart the production of phenolics - chemicals that act as a plant's natural defence and are also beneficial to our health. Fertilisers, however, seem to boost the levels of anti-cancer compounds.

Flavonoids are phenolic compounds that have potent antioxidant activity. Many are produced in plants in response to environmental stressors, such as insects or competing plants.

"If an aphid is nibbling on a leaf, the plant produces phenolics to defend itself,"​ said Mitchell. "Bitter or harsh phenolics guard the plant against these pests."​

The need for these natural safeguards decreases with the use of herbicides and pesticides in conventional agriculture. This decrease is reflected in the total amount of antioxidants the plants produce.

"This helps explain why the level of antioxidants is so much higher in organically grown food,"​ added Dr. Mitchell.

"By synthetically protecting the produce from these pests, we decrease their need to produce antioxidants. It suggests that maybe we are doing something to our food inadvertently."​

Mitchell's investigation involved the total antioxidants found in foods grown organically (using no herbicides, pesticides or fertilizers) to foods grown sustainably (in this study fertilizers but no herbicides or pesticides were used) and conventionally (using synthetic chemicals to protect the plants and increase yield).

The results showed a significant increase in antioxidants in organic and sustainably grown foods versus conventionally grown foods. The levels of antioxidants in sustainably grown corn were 58.5 per cent higher than conventionally grown corn. Organically and sustainably grown marionberries had approximately 50 per cent more antioxidants than conventionally grown berries. Sustainably and organically grown strawberries showed about 19 per cent more antioxidants than conventionally grown strawberries.

Of particular interest is the finding that antioxidant levels were highest overall in sustainably grown produce, indicating that a combination of organic and conventional practices yields the highest levels of antioxidants.

"This may reflect the balance between adequate nutrition in the form of fertilisers and external pest pressures because of the lack of pesticides and herbicides,"​ explained Mitchell.

Full findings appear in the 26 February print edition of the Journal of Agricultural and Food Chemistry​.