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Biological Chemistry

Organic onions are richer in flavonoids

A six-year comparison of organic versus conventional onions shows higher levels of phytochemicals thought to promote health

by Alla Katsnelson
July 3, 2017 | APPEARED IN VOLUME 95, ISSUE 27

Credit: Shutterstock
Organically grown Red Baron onions (shown) have higher levels of flavonoids, on average, than conventionally grown ones.
Credit: Shutterstock
Organically grown Red Baron onions (shown) have higher levels of flavonoids, on average, than conventionally grown ones.

Many shoppers believe organic vegetables are healthier than their conventionally grown counterparts. But previous studies of differences between the two types of produce have relied on vegetables bought off the shelf or have encompassed just a couple of years of side-by-side growth, making it difficult to rule out the effects of annual differences in weather or other factors. Researchers from the Teagasc Ashtown Food Research Centre have now compared organic and conventional cultivation of two varieties of onions grown in the same location over six seasons. They report that organic onions contain a significantly higher amount of two types of flavonoids, which are compounds that some studies have shown may protect against chronic health conditions such as cardiovascular disease, diabetes, and cancer (J. Agric. Food Chem. 2017, DOI: 10.1021/acs.jafc.7b01352). Between 2009 and 2014, the team grew Red Baron (red) and Hyskin (yellow) onions using both conventional cultivation, which includes the use of mineral fertilizers and synthetic pesticides, and European Union organic farming methods, which largely exclude those practices. They analyzed the compounds, including red anthocyanin flavonoids and the yellow flavonoid quercetin, in freeze-dried onion extracts using high-performance liquid chromatography and other techniques. Overall, the total flavonoid content was 10 to 50% higher by dry weight in the organic onions. The team attributes the flavonoid gap primarily to the differences in soil management and pest control. In organic farming, plants experience more stress, explains study author Dilip K. Rai, which prompts them to generate secondary metabolites such as flavonoids as a defense mechanism.



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