It's in the brew: coffee antioxidants formed by roasting

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  • Published: Mar 1, 2011
  • Author: David Bradley
  • Channels: UV/Vis Spectroscopy
thumbnail image: It's in the brew: coffee antioxidants formed by roasting

Truly roasted

UV-Vis spectroscopy and fluorescence studies reveal that the antioxidants in coffee with the most potent assumed health benefits are formed by the roasting of beans rather than being present in the raw green beans. The results are reported in detail in the journal Food Research International.

There is much evidence that dietary antioxidants are an important component of nutrition. Antioxidants are thought to assist in the removal of oxidising free radicals, which are commonly the end products of various metabolic processes and have been linked to the aging process and various disease states. Many research teams have focused on leafy vegetables, brightly coloured fruits, green tea, chocolate, red wine and coffee, all hoping to demonstrate the benefits of given food stuff based on chemical content. Coffee may have had a bad press on the basis of certain aspects of its stimulant activity due to caffeine. However, for every research paper pointing out a putative health problem associated with drinking large quantities of coffee, there seems to be a study that counters those problems by highlighting the positive effects of antioxidants present in raw coffee beans.

Now, food scientists at the University of British Columbia in Vancouver, Canada, have now used UV-Vis and fluorescence techniques to focus on the complex chemistry underpinning the conversion of natural products found in green coffee beans into antioxidant end-products during the process of roasting.

Common antioxidants

Yazheng Liu, David Kitts found that the most common antioxidants present in a cup of dark roasted coffee result not from inherent compounds in the raw beans but from the browning process itself, the high-temperature Maillard reaction, commonly associated with roasting and baking. The Maillard reaction discovered by chemist Louis-Camille Maillard in the early part of the twentieth century involves the endothermic reaction of an amino acid and a reducing sugar. It is an essential part of the development of colour, texture and aroma of many foods, such as roast chicken, grilled steak or baked bread and, like caramelization, is a form of non-enzymatic browning.

"Previous studies suggested that antioxidants in coffee could be traced to caffeine or the chlorogenic acid found in green coffee beans, but our results clearly show that the Maillard reaction is the main source of antioxidants," explains Liu, who is studying for a Master's degree in the Faculty of Land and Food Systems (LFS). Kitts, who is an LFS food science professor and director of the Food, Nutrition and Health program, adds that, "We found, for example, that coffee beans lose 90 per cent of their chlorogenic acid during the roasting process." The team reports that: "Data from this study suggested that natural phenolics present in non-roasted coffee beans had higher antioxidant activity compared to Maillard reaction products (MRPs) derived from coffee and model Maillard Reaction systems. However, MRPs were the prevailing antioxidants in roasted coffee." They further explain that the likely mechanisms of the antioxidant action associated with coffee Maillard reaction products involved hydrogen atom transfer and single electron transfer mechanisms.

The UBC study might help resolve the inconsistent findings regarding coffee and antioxidants. While some scientists report increased antioxidant activity in coffee made from dark roasted beans, others found a decrease. Yet other theories insist that medium roast coffees yield the highest level of antioxidant activity. Quite bizarrely, some research has suggested that simply breathing in the aroma of roasted coffee beans can provide a dose of antioxidants for those who enjoy the smell but would prefer not to drink coffee.



The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

 UV-Vis spectroscopy and fluorescence studies reveal that the antioxidants in coffee with the most potent assumed health benefits are formed by the roasting of beans rather than being present in the raw green beans. The results are reported in detail in the journal Food Research International.

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