L.H. Skibsted


Aerobic life has been challenged by the changing conditions appearing through evolution resulting in appearance of both hydrophilic and lipophilic antioxidants as an indispensable protection against the ubiquitous reactive oxygen- and nitrogen species. Interaction between hydrophilic and lipophilic antioxidants at interfaces often results in synergistic effects important for food stability. Such concerted actions by antioxidants also seem of relevance for human nutrition, but need a more mechanistic description. Non-vitamin antioxidants like the hydrophilic polyphenols including their glycosides thus show synergism through enhancing the lipophilic tocopherols as chainbreaking antioxidants. While this tocopherol/polyphenol synergism seems to be controlled kinetically, the synergism between the lipophilic tocopherols and the lipophilic carotenoids is rather thermodynamically controlled through a regeneration of the carotenoids by the tocopherols. Antioxidant interaction between carotenoids and polyphenols is less investigated and more complex, but may explain the special role of the non-vitamin carotenoids as antioxidants. Carotenoids act as electron donors reducing lipid radicals in membranes subsequently being regenerated at interfaces by hydrophilic polyphenols. Taking distribution phenomena into account, a kinetic description may be possible. Carotenoid radical cations of the less reducing carotenoids like astaxanthin is regenerated faster to form the parent carotenoids showing the importance of the keto group for electron transfer in favour of kinetic control as is further confirmed by linear-free-energy relationships.