EPR spectroscopy: A tool to characterize stability and antioxidant properties of foods
2006
Polovka, M.(Food Research Institute, Bratislava (Slovak Republic))
The antioxidant status of foods and plant products is nowadays widely characterized by means of various analytical and spectroscopic methods. In the present work, the thermal stability of lager beers and the influence of ascorbic acid addition on their stability, as well as the antioxidant properties of commercial teas and wines have been studied by means of EPR spin trapping technique, using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO); alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN) and alpha-phenyl-N-tert-butylnitrone (PBN) as spin traps in various, mostly oxygen-centred radicals producing systems; as well as by means of stable free radicals 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPOL). The thermal stability of lager beer can be well characterized by means of spin trapping agent PBN. The addition of L-ascorbic acid (ASC) to the beer samples accelerated the radical processes and a lower stability was found. The highest antioxidant potential to terminate superoxide radicals in tea solutions was found in green tea, followed by black and fruity teas. The influence of Mn2+ and ascorbic acid presence on the antioxidant properties of tea samples was also tested. Various sources of free radicals used in the antioxidant tests, due to their specific action, show different termination rates in the presence of the individual tea samples. The radical scavenging abilities of 30 samples of Tokay wines from the Slovak region were compared with 10 samples of red and 10 samples of white wines originating from various regions. The results showed that the Tokay wines have a very good scavenging ability, positioned between the white and red wines.
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