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Organically grown carrots and onions match conventionally grown antioxidant levels

By Nathan Gray , 05-Nov-2010
Last updated on 15-Nov-2010 at 09:12 GMT

Organically grown produce may offer no nutritional benefits over traditional growth methods, according to a new study.

Published in the Journal of Agricultural and Food Chemistry, the study reports new evidence that organically grown onions, carrots, and potatoes generally do not have higher levels of polyphenol antioxidants than vegetables grown with traditional fertilizers and pesticides.

“On the basis of the present study carried out under well controlled conditions, it cannot be concluded that organically grown onions, carrots, and potatoes generally have higher contents of health-promoting secondary metabolites in comparison with the conventionally cultivated ones,” stated the researchers, led by Pia Knuthsen from the National Food Institute at Technical University of Denmark.

The new study adds further confusion to the ongoing debate on whether organically grown fruit and vegetables are any more nutritious than their traditionally cultivated counterparts.

Organic vs Conventional: Controversial

The fundamental differences between organic and conventional agricultural systems are in fertilization strategy and soil fertility management, which in theory affect the nutrient composition in plants and provide healthier better tasting produce. However, previous studies on the nutrient content of organically and conventionally grown plants have generated contradicting results.

In 2009 an FSA review on the nutritional content of organic and conventional produce sparked controversy after it concluded that there are no differences. The research conducted at the London School of Hygiene and Tropical Medicine concluded that “there is no evidence to support the selection of organically produced foodstuffs to increase the intake of specific nutrients or nutritionally relevant substances.”

However, several smaller studies have since reported higher levels of certain nutrients in organically grown produce, including strawberries . In addition, a French review completely contradicted the findings of the FSA concluding that “organic plant products contain more dry matter and minerals – such as iron and magnesium – and more antioxidant polyphenols like phenols and salicylic acid.”

Knuthsen and colleagues pointed out that there are many reasons to pay a premium for organic food products, including improved animal welfare, environmental protection and better taste and freshness. However, they noted that the health benefits of organic food consumption are still controversial and not considered scientifically well-documented.

“The objective of our study was to compare the content of selected flavonoids and phenolic acids in organically and conventionally grown onions, potatoes, and carrots and to evaluate if the ability of the crops to synthesize selected secondary metabolites is systematically affected by growth systems across different growth years as well as geographic locations [and soil types],” stated the authors.

Nutritional value

The researchers reported that onions and carrots, showed no statistically significant differences between growth systems for any of the analyzed polyphenols over a two year growing period.

Organically grown potatoes fertilized with cover crops, were however observed to have a higher content of one polyphenol – chlorogenic acid (5-CQA) – compared to the conventional growth system.

No benefit?

The researchers concluded that, based on the results of their study, it cannot be concluded that organically grown onions, carrots, and potatoes have higher contents of polyphenols and related secondary metabolites, in comparison with conventionally cultivated ones.

“The ability of crops to synthesize selected secondary metabolites was not systematically affected by the growth system across different growth years and geographical locations,” they stated.

However, some commentators have previously pointed out that nutrition is not the main reason that many people opt for organics, stating that the avoidance of pesticides and consumer preference for produce grown using land-conscious practices account for much of the sector.

Source: Journal of Agricultural and Food Chemistry
Volume 58, Issue 19, Pages 10323–10329, doi: 10.1021/jf101091c
“Effects of Organic and Conventional Growth Systems on the Content of Flavonoids in Onions and Phenolic Acids in Carrots and Potatoes”
Authors: M. Søltoft, J. Nielsen, K. Holst Laursen, S. Husted, U. Halekoh, P. Knuthsen

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