The findings are reported in the August 14 issue of the Journal of Agricultural and Food Chemistry, a peer-reviewed publication of the American Chemical Society, the world's largest scientific society.
Sweet corn is the number-two processed vegetable in the United States, second only to tomatoes, according to Rui Hai Liu, M.D., Ph.D., assistant professor of food science at Cornell University and lead author of the paper.
The study shows that heat processing of sweet corn, which is how canned corn is prepared, increases both total antioxidant activity and the level of phenolics -- a naturally occurring type of phytochemical found in many fruits and vegetables. Heating sweet corn, whether it is on the cob, in a casserole, or in the can, enhances its beneficial compounds, Liu noted.
Processing at 115 degrees Celsius for 25 minutes elevated total phenolics by 32 percent, with ferulic acid -- the predominant phenolic compound in sweet corn -- increasing by 550 percent.
"It's conventional wisdom that processed fruits and vegetables have lower nutritional value than sweet fresh produce," Liu said. This is because processing leads to a decrease in vitamin C -- an antioxidant that prevents cell and tissue damage and purportedly gives fruits and vegetables their disease-preventing abilities.
But Liu's ongoing investigation of fruits and vegetables contradicts conventional wisdom.
In one study, published two years ago in Nature, Liu and his team found that less than 0.4 percent of an apple's antioxidant activity comes from vitamin C. Instead, a combination of phytochemicals supplies the antioxidants in apples. This led Liu to suspect that processed fruits and vegetables might actually maintain their antioxidant activity despite the loss of vitamin C.
Earlier this year, in another study published in the Journal of Agricultural and Food Chemistry, the researchers reported more evidence that processing is beneficial. They found that cooking tomatoes triggers a rise in total antioxidant activity, chiefly due to an increase in lycopene -- a phytochemical that makes tomatoes red.
The findings are obviously good for the processing industry, Liu said, but they are also good for the consumer: "It doesn't matter if it's raw; it doesn't matter if it's cooked; it doesn't matter if it's fresh; it doesn't matter if it's processed. You simply need to eat a variety of fruits and vegetables to get maximum health benefits."
Liu's coauthors were Cornell graduate student Veronica Dewanto and a visiting fellow in Liu's laboratory, Xianzhong Wu. The research was funded by Cornell University and the United States Department of Agriculture's Federal Formula Fund.
— Jason Gorss
Journal
Journal of Agricultural and Food Chemistry