October 19, 2004

Onions May Prevent Cancer

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In a recent study published in the October issue of the Journal of Agricultural and Food Chemistry, Cornell researchers confirmed that different varieties of onions offer different degrees of health benefits.

“Some onions have higher antioxidant activities and higher antiproliferative activity than others,” said Prof. Rui Hai Liu, food science, head investigator of the study.

All onions, and many other fruits and vegetables, possess strong concentrations of antioxidants, compounds that are thought to be beneficial to human health because they neutralize free radicals. Free radicals are harmful substances typically produced when oxygen interacts with certain molecules to form electron deficient compounds that are highly reactive. Often times, these radicals are natural by-products of human metabolism and removed by the body, but when left unchecked they can quickly cause damage to cells or even cancer. That is why high levels of antioxidants are “correlated with activity that inhibits cancer growth,” Lui said.

But flavonoids, the particular antioxidants found in onions, vary in concentration between different onion species. In general, “onions grown in colder climates have higher antioxidant activity,” Lui said. Also, the not so popular “pungent onion [varieties] appear to have more flavonoid compounds and be more healthy,” Lui added.

Yet cooking onions to tame their bitter taste does not seem to alter their nutritional value, according to Joy Emilie Swanson, nutritional science. During cooking “some [antioxidants] will be degraded, but [others] are activated because they are bound within the flesh of the onion — so cooking releases that,” said Swanson.

“The shallots had the highest antioxidant activity, followed by the Western Yellow, New York Bold and Northern Red,” said Jun Yang grad, food science, member of Lui’s research group.

The study primarily consisted of employing an antioxidant measuring procedure to determine the flavonoid content in each onion variety.

“Flavonoid is a class of compounds — probably 4,000 or 5,000 specific compounds belong to flavonoids,” Yang explained.

The measuring technique, which was developed at Cornell by the same research group, counted the total concentration of all flavonoid compounds in each onion species.

Antioxidant diversity is greatly linked to the health benefits they provide, according to Swanson. This is because, an assortment of many different types of antioxidants tend to neutralize free radicals more efficiently than a single version. Since onions contain only one class of antioxidants, if one onion variety were to constitute your daily antioxidant consumption, “you would be missing a lot of other types of flavonoids that are in other products,” said Swanson.

It is believed that different onion varieties also contain different types of flavonoids, according to Yang.

Though the study was concerned primarily with genetic differences in antioxidant concentration, the fact that those groups grown in colder climates demonstrated higher concentrations may suggest an environmental correlation. “Sometimes [higher antioxidant concentration] could be related to the climate stress-maybe in colder temperatures, they produce more phytochemicals,” Yang said.

Lui agreed, but also suggested that food processing may effect the overall concentration.

“We should look at the effect of the processing on the antioxidant activity,” Lui said, “we will continue working on it.”

The entire study began about two years ago, but has been focused on onions over the past 10 months.

Future projects include a study of changes in antioxidant concentration in grapes during wine making and an analysis of food processing on antioxidants in onions.

Archived article by David Andrade
Sun Staff Writer