The researchers from the Monash University and the University of Melbourne in Australia looked at both the Arabica coffee bean itself and what happened to its stable free radical and antioxidant properties after the brewing process.
Earlier research had suggested roasting coffee beans could destroy stable antioxidants like chlorogenic acids found naturally in the green coffee beans said to protect the body’s cells from damage.
These antioxidants are replaced with a different class of antioxidants called Maillard reaction products (MRP).
Published in the journal Plos One, the results of this latest in vitro study suggested that a number of stable radical species were formed during roasting and their intensity varied with roasting time and the subsequent grinding and ageing process.
The study was part-funded by the Italian coffee-roasting company illycaffé.
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They said the chemical make-up of the antioxidant activity in coffee brews was "complex".
Several polyphenols were present in green coffee beans and during roasting these were converted into a plethora of compounds. At the same time, the beans went through the Maillard reaction and browning, which saw a number of compounds with a wide range of molecular weights.
Using electron paramagnetic resonance (EPR) spectroscopy, the researchers saw various changes to the distribution of species when the ground beans were aged for one month in a sample tube. For example the total radical signal detected was increased at roasting times over six minutes.
The researchers said this could be due to the gradual decrease in water content during exposure of the grounds to air, leading to improved microwave penetration depth and number of spins detected.
They found the anti-radical activity of brewed coffee was dominated by low molecular weight phenolic compounds.
Source: Plos One
Published online ahead of print, doi: 10.1371/journal.pone.0122834
"Stable Radical Content and Anti-Radical Activity of Roasted Arabica Coffee: From In-Tact Bean to Coffee Brew"
Authors: G. J. Troup, L. Navarini, F. Suggi Liverani, S. C. Drew