A novel antioxidant activity index (AAU) for natural products using the DPPH assay

A novel antioxidant activity unit (AAU) was proposed as the antioxidation ability of natural products using the DPPH assay. Based on the definition of AAU, using a combination of fitting curve equation for scavenging ratio of DPPH free radicals with the theoretical relation between DPPH concentration and absorbance, the equation was deduced. In this study, eight – lignans and the standard samples of gallic acid, vitamin C were used. It was demonstrated that the concentration of DPPH was affected more by temperature than by time; AAU showed its consistency and uniqueness between different concentrations of each lignan with a relative standard deviation (RSD) of less than 8.07%. The antioxidant strength of plant extracts and pure compounds were compared. Analysis of the antioxidant activity of lignans in relation with their structure factors was made.