The oxidative stability of myrtle hydroalcoholic extracts was measured, over storage time, with the EPR spin trapping method under forced ageing conditions. The extracts were prepared with 150 and 300 g l-1 of berries and extraction media with ethanol ranging from 60 to 90%. Two radicals were detected: the PBN-1-hydroxyethyl adduct and the tert-butyl aminoxyl radical. A dimensionless parameter (Ω) calculated on the basis of the lag time, the rate of formation and concentration of the radical species was used to estimate the extracts' oxidative stability. Ω was strongly influenced by the extraction medium, being lower in extracts with ethanol 60%, and by the time of storage. An inverse correlation was calculated between Ω and ellagic acid concentration, thus suggesting the role of this phenolic acid in the antioxidant properties of the extracts. The radical scavenging activity of the extracts against the hydroxyl radical was also measured.
Keywords: EPR; Hydroxyl radical scavenging activity; Myrtle extracts; Oxidative stability.
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