Applicability of the DPPH assay for evaluating the antioxidant capacity of food additives - inter-laboratory evaluation study

An inter-laboratory evaluation study was conducted in order to evaluate the antioxidant capacity of food additives by using a 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay. Four antioxidants used as existing food additives (i.e., tea extract, grape seed extract, enju extract, and d-α-tocopherol) and 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox) were used as analytical samples, and 14 laboratories participated in this study. The repeatability relative standard deviation (RSD_r) of the IC₅₀ of Trolox, four antioxidants, and the Trolox equivalent antioxidant capacity (TEAC) were 1.8 - 2.2%, 2.2 - 2.9%, and 2.1 - 2.5%, respectively. Thus, the proposed DPPH assay showed good performance within the same laboratory. The reproducibility relative standard deviation (RSD_R) of IC₅₀ of Trolox, four antioxidants, and TEAC were 4.0 - 7.9%, 6.0 - 11%, and 3.7 - 9.3%, respectively. The RSD_R/RSD_r values of TEAC were lower than, or nearly equal to, those of IC₅₀ of the four antioxidants, suggesting that the use of TEAC was effective for reducing the variance among the laboratories. These results showed that the proposed DPPH assay could be used as a standard method to evaluate the antioxidant capacity of food additives.