Probing Free Radical Processes during Storage of Extracts from Whole Roasted Coffee Beans: Impact of O2 Exposure during Extraction and Storage

Development of liquid coffee products of good quality with extended shelf lives is hampered by their rapid quality degradation as a result of both physical and flavor instability. One approach that is being considered for extending the shelf lives of liquid coffees is that of supplementing the beverage with a very mild and slow continuous extraction from intact roasted beans that are held within an aluminum can. This paper reports the use of electron paramagnetic resonance (EPR) spectroscopy to examine the effects of key parameters that affect the stability of liquid coffee prepared from aqueous extracts from whole roasted coffee beans, namely, the O-2 content of the water and headspace during extraction and the temperature during storage. It was found that the magnitude of the free radical signal was sensitive to the O-2 content of the water used for extraction and storage time and temperature, whereas the intensity of the Fe(III) (g = 4.3) signal was affected only by the O-2 content of the water and the Mn signal was insensitive to the experimental parameters. The most critical factor was the O-2 content of the water used for extraction, and careful control of O-2 exposure at the extraction stage could be a crucial factor for generating products with resistance to oxidative processes during storage.