The main source of antioxidants in coffee is not the uncooked green beans, but can be traced to “valuable compounds” in the roasting process, according to a new study.
Writing in Food Research International, scientists at University of British Columbia attempted to shed some light onto the cause and nature of the “stable antioxidants” found in coffee, which are said to protect the body’s cells from damage and aging.
Previous studies in this area have had conflicting results, citing factors such as the brewing methods or source of the beans as the cause of the naturally occurring antioxidants.
The Maillard reaction
According to the researchers, the study confirmed that green unroasted coffee beans contain natural antioxidants (chlorogenic acids), which are said to have antibacterial properties. However, the scientists claim their research shows that about 90 per cent of these acids are destroyed by the roasting process.
In turn, the roasting creates a whole new class of potent antioxidants called maillard reaction products (MRP).
The term refers to the work by 1900s French chemist Louis-Camille Maillard who looked at how heat affects the carbohydrates, sugars and proteins in food.
“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,” said Liu, an MSc student in the Faculty of Land and Food Systems (LFS).
Methodology and results
The chemical characteristics related to the antioxidant activity of roasted coffee were evaluated, using non-roasted coffee beans and model Maillard reaction products (MRPs) as controls.
The formation of MRPs and the degradation of phenolics in roasted coffee were investigated by using fluorescence, UV-vis spectra and tri-stimulus color parameters which were measured on both the roasted coffee and the two controls.
Total chlorogenic acid and caffeine contents in non-roasted coffee beans and roasted coffee extracts were also quantified using high performance liquid chromatography.
Both roasted coffee and the controls showed high antioxidant activity in three chemical based tests, irrespective of caffeine content.
Data from the study suggested that natural phenolics present in non-roasted coffee beans had higher antioxidant activity compared to the MRPs derived from coffee and model MR systems. However, MRPs were the prevailing antioxidants in roasted coffee resulting in a 90 per cent loss of chlorogenic acid.
Source: Food Research International
Confirmation that the Maillard reaction is the principle contributor to the antioxidant capacity of coffee brews,
Published online ahead of print: doi: 10.1016/j.foodres.2010.12.037
Authors: Y. Liu & D.D. Kitts