Coffee is known to have certain antioxidant qualities. In order to understand the source and mechanism of this quality, a study was conducted to look into the chemical nature of roasted coffee, with respect to its antioxidant properties. The chemical components obtained from roasting coffee beans at high temperatures were analyzed and quantified. The results showed that in roasted coffee, compounds called Maillard reaction products (MRPs) had high antioxidant properties. It was also seen that roasted coffee with higher amounts of low molecular weight MRPs demonstrated higher antioxidant properties. The actual antioxidant properties of coffee arise due to its roasting process.
When green coffee beans are roasted, they are subjected to very high temperature conditions (about 390 to 480 F). The conditions associated with this processing lead to complex physical as well as chemical transformations in the coffee beans and heat-induced degradation of certain compounds like chlorogenic acid (CGA) that are thought, by some researchers, to impart antioxidant properties to the coffee. This degradation also leads to formation of certain compounds called Maillard reaction products (MRPs). Earlier studies have shown that “the antioxidant activity of coffee is in fact mostly dependent on the roasting conditions, much more so than brewing methods and the source of coffee beans.” However there has been no consistency in the various studies that have investigated the effect of roasting on the antioxidant property of coffee. This study was conducted to understand the basis of antioxidant action in typically roasted coffee beans.
* Coffee beans (Coffea arabica) were subjected to roasting at different temperatures to obtain samples of varied degrees of roasting.
* Compounds mimicking Maillard reaction products (MRPs) were also prepared.
* Extracts were made of the roasted coffee beans, MRPs and raw or non-roasted coffee beans and subjected to various physical and chemical analyses.
* The samples were also analyzed for their caffeine concentration and antioxidant properties using sophisticated assay techniques.
* On comparing the color of the samples, it was noted that browning was higher in the MRPs than in the roasted coffee. The authors speculate that this is because of higher concentrations of the chemicals known as melanoidins.
* The results also show that antioxidant properties in roasted coffee are mainly due to the presence of MRPs, which are produced after roasting the coffee. MRPs that are low in molecular weight led to stronger antioxidant property while high molecular weight MRPs (melanoidins) contributed less to antioxidant properties.
* The mechanism of the action of antioxidants was also found, which was by way of hydrogen atom transfer and single electron transfer to oxidants.
The results of this study show that contrary to what was earlier believed, it is not caffeine or low molecular weight compounds like CGA that contribute to the antioxidant characteristics of coffee, but the MRPs that “are the prevailing antioxidants present in dark roasted coffee brew extracts.” This study also demonstrates that MRPs of different weights act as antioxidants in different ways; the mechanism of antioxidation is by means of transfer of hydrogen atoms and single electrons. In summation the authors state, “The loss of CGA and possibly other nature antioxidants in the coffee bean, combined with the generation of MRPs attributed to the high temperatures used in roasting, ultimately influenced the composition and thus the antioxidant activity of the final product.”
For More Information:
Confirmation that the Maillard Reaction Is the Principle Contributor to the Antioxidant Capacity of Coffee Brews
Publication Journal: Food Research International, 2011
By Yazheng Liu and David D. Kitts; University of British Columbia, Vancouver, British Columbia, Canada