Found on tables everywhere from breakfast to dinner, coffee is one of the world’s most widely consumed beverages. With its distinctive taste and stimulant effects, people have been drinking coffee for pleasure for centuries. But some cultures have also believed in its medicinal properties. Only recently, these notions have been vindicated by research that is allowing us to understand the benefits of consuming coffee and what they could mean for our health.
Previously, much of the research into the nutritional value of coffee was focused on caffeine. But in an individual cup of coffee there are actually 1000s of compounds, many of which may have in vitro activity.
One group of compounds found in coffee that have well-established antioxidant properties are the polyphenols. These are present in large quantities in unroasted green coffee beans. However, when the beans are roasted before being used to make a brew, some of these polyphenols are converted into other compounds.
One type of compound produced during this process is known as melanoidins. These contain stable radicals and could have antioxidant activity. However, the extent to which melanoidins contribute to antioxidant activity in a brewed cup of coffee has been uncertain.
A recent study by Troup et al (2015) went some way to shedding light on this. The researchers used a method known as electron paramagnetic resonance (EPR) spectroscopy to measure and characterize the activity of radicals in coffee beans, depending on how long they had been roasted for.
To carry out their measurements, the team used a Bruker E500 X-band spectrometer fitted with a Bruker super-high-Q probehead. This gave them a highly sensitive means by which to assess radical activity.
Studying ground and intact beans, the researchers identified three distinct radical species. They found that the longer beans had been roasted for, the greater intensity they showed on spectroscopy. This suggests that longer roasting increases the formation of stable radicals in coffee.
But, the researchers found that this was not responsible for the antioxidant properties of the final brew. By making drinks of coffee from these beans, they showed that the antioxidant activity in coffee could be mostly attributed to the fraction of the drink containing polyphenols themselves, and not the fraction that contained melanoidins and the stable free radicals.
The researchers conclude that stable radicals in roasted coffee beans are therefore not related to the anti-radical activity of drinks made from those beans. They add, however, that this does not exclude the possibility they have other effects, such as non-antioxidant ones.
Troup et al say that future studies using EPR could help to further understand how radicals are formed in coffee beans during roasting and where they originate from in the intact coffee bean. The technique could thereby allow us to trace the complete journey of radicals in coffee from bean to cup.
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Troup, G et al. Stable Radical Content and Anti-Radical Activity of Roasted Arabica Coffee: From In-Tact Bean to Coffee Brew. PLoS One 2015; 10: e0122834.
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