Comparison of electrochemical and spectrometric methods in the antioxidant activity evaluation of some fruits from north of Iran

The antioxidant capacity is defined as the ability of compound (or mixture of compounds) to inhibit the oxidative degradation of various compounds like preventing lipid peroxidation. These methods are usually based on the direct reaction between studied compounds and free radicals (quenching or scavenging) or on the reaction with transition metals [1]. Spectrometric methods are mainly used in the analysis of antioxidant properties. However, these methods are dependent on many parameters, such as: temperature, analysis time, character of a compound or mixture of compounds (extracts), concentration of antioxidants and prooxidants and many other substances [2,3]. Electrochemical methods used for the determination of antioxidant capacity have been still developing. These provide rapid, simple and sensitive alternative methods in the analysis of bioactive compounds associated with the scavenging of the radicals as well as the antioxidant capacity itself. They are low-cost and usually do not require time consuming sample preparation [4]. In the present work, we investigated electrochemical evaluation of antioxidant capacity of persimmon and hawthorn fruits from north of Iran. Hence, definite amounts of dried persimmon and hawthorn samples were weighted and then extracted with different solvents such as ethanol and methanol by soxhlet. After extraction, 250 μL of obtained extracts was diluted with 15 mL of phosphate buffer 0.1M (pH 5.5). Electrochemical responses were obtained with a three electrode system consisting of a glassy carbon electrode, a Pt wire and the Ag/AgCl/KCl 3M representing the working electrode, the counter electrode and the reference electrode, respectively. The antioxidant and redox profile of fruits extracts were characterized by means of cyclic voltammetry and differential pulse voltammetry. The 13th Annual Electrochemistry Seminar of Iran Materials and Energy Research Center (MERC), 22- 23 Nov, 2017 60 antioxidant potential expressed by electrochemical index (EI) was compared to the results obtained with the 2,2-diphenyl-1-picrylhydrazyl (DPPH) method. Each extract was dissolved in an appropriate volume of water to give final concentrations ranging from 50.00 to 300.00 μg/mL. Standard ascorbic acid solutions were also prepared in water to give the same concentration range. 1.5 mL of each solution was transferred to a test tube and mixed with 1 mL of 0.3 mmol/L DPPH. A control solution was prepared by adding methanol (1.5 mL) to 0.3 mmol/L DPPH (1 mL). The experiment was run in triplicate. The solutions were mixed well and left in the dark for 30 min. After 30 min the solutions were analyzed on a UV–vis spectrophotometer at 517 nm. The percentage of antioxidant potential was calculated using the formula: % Inhibition = Ac−AsAc ×100 where, Ac is absorbance of the control solution, As is absorbance of the sample or standard. Also, the extracts were analyzed by Gas chromatography–mass spectrometry (GC-MS).