Organically-grown oranges contain up to 30 per cent more vitamin C than those grown conventionally, a meeting of the American Chemical Society heard this week.
Theo Clark, a visiting chemistry professor at Truman State University, Missouri, reported the finding based on work done by him and a group of undergraduate students. He said he decided to conduct the analysis because of a lack of analytical information about the nutritional content of organically-grown produce.
"Quite often, organic goods come from smaller farms that market their goods with provocative labels such as 'healthy,' 'delicious,' or 'natural'," he said. "These statements are generally made without reference to any comparable standards."
Clark added that he chose oranges to begin the assessment because they are high-profile fruits. "The orange is the traditional source of vitamin C, and it is highly commercialised, but no one to our knowledge has thought to compare the organic and conventionally-grown oranges."
Conventional oranges are larger than organically-grown oranges, and they have a deeper orange colour. Because of their size, "we were expecting twice as much vitamin C in the conventional oranges," said Clark.
But to his surprise, chemical isolation combined with nuclear magnetic resonance (NMR) spectroscopy revealed that the organically-grown oranges contained 30 per cent more vitamin C than the conventionally-grown fruits - even though they were only about half the size.
Clark said the reason for the additional nutritional benefits was not clear, although he added: "We speculate that with conventional oranges, (farmers) use nitrogen fertilisers that cause an uptake of more water, so it sort of dilutes the orange. You get a great big orange but it is full of water and doesn't have as much nutritional value."
Clark continued: "However, we can only speculate. Other factors such as maturity, climate, processing factors, packaging and storage conditions require consideration."
In addition to the chemical analysis, Clark and his team conducted a survey of 27 households (approximately 71 individuals) in the rural town of Miller, Missouri, to gauge their expectations of organic oranges. Eighty five per cent of respondents believed that organic oranges would have a higher nutritional content than their conventionally-grown counterparts, and Clark's research shows that "they were right on."
However, 65 per cent believed that there was little or no price difference between the two types of oranges. In fact, Clark's team found that organic oranges cost an average of twice as much.
Clark claimed these issues were important because consumers had a right to know the real nutritional content of organic produce, and hard numbers such as the vitamin C content could validate the claims of the burgeoning organic industry.
On the other hand, farmers considering a change from conventional to organic farming methods needed to know what consumers expected, and what they were willing to pay for it, he said.