The new study, published in the Journal of Agricultural and Food Chemistry, reports that tomatoes grown organically contained higher levels of quercetin and kaempferol aglycones than their conventionally grown counterparts. According to a study published recently in the Journal of the Science of Food and Agriculture, the world market for certified organic foods was estimated at $23-25 bn (€17.3-18.8 bn) in 2003 with annual growth of about 19 per cent.
Alyson Mitchell from the University of California-Davis, and researchers from University of Minnesota studied the levels of quercetin and kaempferol aglycones in dried tomato samples (Lycopersicon esculentum L. cv. Halley 3155) between 1994 and 2004. The tomatoes were grown and processed conventionally or organically. Mitchell and co-workers report that organic tomatoes contained on average 79 and 97 per cent more quercetin and kaempferol aglycones than conventionally grown tomatoes.
The explanation for these observations was that 'over-fertilisation' of the conventionally grown plants. Flavonoids are produced as a defence mechanism of the plant in response to nutrient deficiency. In the organically grown plants, no fertilisation occurred which was mirrored in increasing levels of the flavonoids over time as the soil fertility decreased. "This increase corresponds not only with increasing amounts of soil organic matter accumulating in organic plots but also with reduced manure application rates once soils in the organic systems had reached equilibrium levels of organic matter," concluded the researchers.
Commenting independently on the research, Lord Krebs, former chairman of the UK's Food Standards Agency (FSA) and now an academic at Oxford, told The Times that higher flavonoid levels do not necessarily mean that organic food is healthier. "This depends on the relevance of the differences to the human body. Tomato ketchup has higher levels of lycopene [a strong antioxidant] than either organic or conventional tomatoes. So if you wanted lots of lycopene you should eat tomato ketchup," he said.
A recent review, published in the journal Nutrition Bulletin and authored by Claire Williamson from the British Nutrition Foundation, stated that the overall body of science does not support the view that organic food is more nutritious than conventionally grown food. "Organic farming represents a sustainable method of agriculture that avoids the use of artificial fertilisers and pesticides and makes use of crop rotation and good animal husbandry to control pests and diseases," wrote Williamson. "From a nutritional perspective, there is currently not enough evidence to recommend organic foods over conventionally produced foods."
Source: Journal of Agricultural and Food Chemistry Published on-line ahead of print, ASAP Article doi: 10.1021/jf070344+ S0021-8561(07)00344-5 "Ten-Year Comparison of the Influence of Organic and Conventional Crop Management Practices on the Content of Flavonoids in Tomatoes"
Authors: A.E. Mitchell, Y.-J. Hong, E. Koh, D.M. Barrett, D. E. Bryant, R.F. Denison, and S. Kaffka