Abstract
Coffees and teas are beverages that are both exceptionally rich in antioxidant molecules, and are also both associated with beneficial health effects. Thus although the quality characteristics of these beverages are conventionally assessed on the basis of their sensory properties, their antioxidant contents represent an additional and increasingly valued attribute of quality based on their contributions to healthy diets. Both beverages are prepared by hot water extraction of a pure plant-derived product, and thus their compositions can potentially change quite rapidly as a result of oxidation in contact with air. Oxidative processes often proceed via free radical intermediates, and sometimes also result in the formation of stable radical end-products; thus EPR spectroscopy is a convenient technique for investigating some of the various free radical reactions that occur in these beverages. This paper reviews progress that has been made in elucidating free radical processes that occur during the preparation and storage of coffees and teas, and the results are discussed in terms of quality criteria of the beverages.
Highlights
Coffees and teas are two of the most heavily consumed beverages in the World
Goodman et al / Agricultural Sciences 4 (2013) 433-442 products of nated form its 1-electron .OOH, as well reads utchteiohny, drOo2 xylanrdadiitcsalpr.OotHo, whereas others, such as its unstable form, 1O2, and hydrogen peroxide, H2O2, are diamagnetic. Both 1O2 and H2O2 readily participate in reactions that lead to free radical generation, and free radicals are a common feature of biological oxidation processes
Since coffee and tea are the major sources of antioxidants in many diets (e.g. [1,2]) and may be stored for long periods in air, it might be expected that oxidation processes could influence their antioxidant contents, or at the very least result in changes in their forms which could impact on the chemical composition of the beverages subsequently prepared by hot water extraction
Summary
Coffees and teas are two of the most heavily consumed beverages in the World. Both have a history of links to medicinal properties, neither is conventionally considered to be a traditional medicine. Goodman et al / Agricultural Sciences 4 (2013) 433-442 products of nated form its 1-electron .OOH, as well reads utchteiohny, drOo2 xylanrdadiitcsalpr.OotHo-, whereas others, such as its unstable form, 1O2, and hydrogen peroxide, H2O2, are diamagnetic Both 1O2 and H2O2 readily participate in reactions that lead to free radical generation, and free radicals are a common feature of biological oxidation processes. [1,2]) and may be stored for long periods in air, it might be expected that oxidation processes could influence their antioxidant contents, or at the very least result in changes in their forms which could impact on the chemical composition of the beverages subsequently prepared by hot water extraction Such reactions are extremely complex, and it is only that we are starting to develop an understanding of the various chemical processes that are involved. The current paper addresses various aspects of the beverage production in which O2-derived free radicals are involved, and illustrates these with results obtained using electron paramagnetic resonance (EPR) spectroscopy, a technique which is based on measurements of chemical species with unpaired electrons, such as free radicals and paramagnetic metal ions and complexes
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