Effect of ambient temperature storage on 2,2-diphenyl-1-picrylhydrazyl (DPPH) as a free radical for the evaluation of antioxidant activity

Abstract

Antioxidants are molecules involved in defense mechanisms against the deleterious effects of free radicals in most organisms. A number of methods are currently being used for the evaluation of the antioxidant
and free-radical scavenging properties of natural and synthetic  antioxidants, including the DPPH method. Numerous speculations about the stability of DPPH solution over a long period of time, at normal ambient temperature have been observed in previous studies but no definite information exists in literature in this regard. Using established protocols, the free-radical capability of DPPH methanolic solution (stored in dark at ambient temperature) was assessed using ascorbic acid as the antioxidant. Results revealed that DPPH methanolic solution gave  comparable free-radical activity 24 hours post preparation compared with the freshly prepared solution. After 24 hours, activity was greatly reduced. We therefore recommend that freshly prepared DPPH solution should be used at all times; however for prolonged experimental schedules, the DPPH solution should be used within 24 hours post preparation, so as to give comparable results with the freshly prepared solution and avoid  ambiguity in results interpretation.

Keywords: Ascorbic acid, methanolic, oxygen species, phytochemicals, stability.