Organic atomic kiwi

Could the claims of the "organic" farming movement be true after all? Analysis of the antioxidant, mineral, and nitrate composition of kiwifruit would suggest so, according to a report in the Journal of the Science of Food and Agriculture. Maria Amodio and Adel Kader of the University of California, Davis, Giancarlo Colelli of the Universita` degli Studi di Foggia, Italy, and Janine Hasey of the University of California, Cooperative Extension, in Yuba City, California, have undertaken a comprehensive study of the constituents of organically grown kiwifruit and reveal that the fuzzy green fruit grown using organic principles contain more health-promoting factors than those grown using conventional methods.

The Davis scientists analysed potassium and sodium levels using atomic absorption spectrometry (AAS). Calcium, phosphorus, boron and magnesium were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES), while total nitrogen was measured using a nitrogen gas analyser in a helium and oxygen environment in a quartz combustion tube and thermal conductivity. Organic acid, sugar composition, and ascorbic acid and dehydroascorbic acid levels were measured using high performance liquid chromatography (HPLC). Total phenolics and antioxidants were determined by absorption spectroscopy.

The team found that organic kiwifruit have significantly higher levels of polyphenolic antioxidants than the conventional counterparts as well as a higher overall antioxidant activity, because of raised ascorbic acid levels. The levels of important minerals were also higher. "All the main mineral constituents were more concentrated in the organic kiwifruits, which also had higher ascorbic acid and total phenolic contents, resulting in a higher antioxidant activity. Sugar and organic acid composition was not affected by the production system," the researchers say. Previous studies have been wholly inconclusive the researchers say.

So, why should organic kiwifruit be richer in compounds beneficial to human health? Kader believes the difference is most likely due to the fruit having to survive against pests in the absence of pesticides. "Conventional agriculture practices utilize levels of pesticides that can result in a disruption of phenolic metabolites in the plant, which have a protective role in plant defense mechanisms," Kadel says. His hunch is further corroborated by the organic kiwifruit having thicker skins as well as the higher antioxidant activity which is thought to be a natural by-product of stress.

However, plants attempting to cope with pest attack also must produce higher levels of secondary metabolites, which act as natural pesticides. Such compounds can affect the toxicological profile of the food. Moreover, some observers suggest that the need for organic farming is misguided given that our bodies have had millions of years to evolve our own defences against a vast range of compounds from natural plant-derived pesticides to the small molecules that are commonly applied to crops in conventional agriculture.