The traditional argument is that fresh fruit and vegetables are better for the health than their processed equivalents, but new research from the US suggests that, at least in the case of corn, the canned variety has significant health advantages.
Scientists from Cornell University, writing in the 14 August issue of the Journal of Agricultural and Food Chemistry claim to have shown that the heat processing of sweetcorn can significantly raise the level of naturally occurring compounds that help fight disease.
Sweetcorn is the number-two processed vegetable in the United States, second only to tomatoes, according to Rui Hai Liu, assistant professor of food science at Cornell University and lead author of the paper.
The study shows that heat processing of sweetcorn, 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 sweetcorn, 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 per cent, with ferulic acid - the predominant phenolic compound in sweet corn - increasing by a massive 550 per cent.
Processing fruit and vegetables decreases the vitamin C content, thereby lowering the product's ability to help prevent cell and tissue damage and reduce the likelihood of disease. However, Liu's research suggests that this does not mean that processed products are less healthy.
In one study, published two years ago in Nature, Liu and his team found that less than 0.4 per cent 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.
It may take more time to convince consumers that processed fruit and vegetables are good for them too - and such information must surely also be tempered with warnings about checking what else is in some of the processed products and which might not be quite so healthy - but this is surely good news for today's consumers who often find it simpler to open a can than prepare food themselves.