Evaluation of antioxidant activity of some plant extracts and their heat stability
Recently, there has been a considerable interest in finding natural antioxidants from plant materials to replace synthetic ones. The search for safe and effective naturally occurring antioxidants is now focused on spices and herbs. In the present study, ethanolic extracts from Mentha x piperita L., Carum carvi L., Petroselinum crispum, Rhamnus frangula, Betula pendula Roth and the mixure „Vitalplant“ (Rhamnus frangula (35%), Mentha x piperita L. (20%), Carum carvi L. (20%), Petroselinum crispum (20%)) were screened for potential antioxidative properties and their heat stability. These properties included iron (III) reduction and 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) scavenging activities. Total phenol and flavonoid contents of each extract were also determined. Heat stability of extracts was investigated by measuring the residual antioxidant activity after heating in a boiling water bath for 15min.
Under the experimental conditions all selected samples exhibited antioxidant activities in both tests. Furhermore, a significant correlation between the results of these tests was obtained (0.80, p<0.05). These results strongly correlate with the total phenol and flavonoid contents of the samples, and according to the obtained results, it phenolics and flavonoids are the major phytochemicals responsible for antioxidant activity in the investigated samples. No significant changes in antioxidant activities were found after thermal treatment.
In addition to being used as medicinal herbs, these plants could also be used as a rich source of natural antioxidants to delay the oxidative deterioration of foods.