Comparison of Extraction Methods for the Determination of Antioxidant Activity in Extracts of Hippophae Rhamnoides L. and Lippia Citriodora. The Effect of Seasonal Collection

In this work, the presence of natural antioxidants has been studied by measuring the antioxidant activity, of two selected samples sea buckthorn (Hippophae rhamnoides L.) and verbena (Lippia Citriodora). Leaves and fruits of two varieties (Leikora and Hergo) of sea buckthorn which are grown in different regions of Greece and verbena leaves grown in the same environment with the variety of sea buckthorn (Leikora) commercially sold as mixtures of the two plants to produce a specific beverage were selected and studied. easonal collection (Leikora variety) of two different crops was studied, in order to investigate the change in the content of antioxidant compounds in the same area at every year of cultivation. Specifically, the aim of this study was to determine the concentration of Total Phenolic Compounds (TPC) in the samples and the assessment of their antioxidant action by different spectrophotometric methods. Extracts were studied using different extraction solvents (methanol/ water 80/20 v/v and water to create beverages). Different extraction methods were compared (Ultrasound Assisted Extraction versus a conventional method) in order to determine the best method of extraction along with the extraction solvent suited for the quantitative release of phenolic components. The total phenolic content was determined by the Folin-Ciocalteu method using gallic acid as the standard and the antioxidant capacity of the plant extracts was measured by their ability to scavenge commercially available free radicals such as (a) DPPH (2,2-diphenyl-1-picrylhydrazyl) and, (b) ABTS (2,2'-azinobis-(3- ethylbenzothiaziline-6- sulfonate) using L- ascorbic acid and Trolox as standards respectively.