Coffee has gone from dietary foe to friend in recent years, partly due to the revelation that it's rich in antioxidants. Now even spent coffee-grounds are gaining attention for being chock-full of these compounds, which have potential health benefits.

In ACS' Journal of Agricultural and Food Chemistry, researchers explain how to extract antioxidants from the grounds. They then determined just how concentrated the antioxidants are.

Maria-Paz de Pena and colleagues note that coffee - one of the most popular drinks in the world - is a rich source of a group of antioxidants called dietary phenolic compounds.

Spent grounds, however, often end up in the trash. But recently, scientists have discovered that antioxidants aren't just in the brewed coffee; they're also in the used grounds. De Pena wanted to figure out the total phenolic content in extracts from these leftovers.

The researchers used three different methods to release antioxidants from spent grounds and found high levels of phenols in the extracts - sometimes at higher levels than in brewed coffee.

Thus, they have the potential to serve as additives to enhance the potential health effects of other food products, the scientists conclude.