In this study, we performed an interlaboratory study of the H-ORAC method (hydrophilic-oxygen radical absorbance capacity), which is an antioxidant potential measuring method using representative antioxidant components, on the basis of the guideline of AOAC International and investigated the accuracy. Eleven laboratories participated, and analyzed five representative antioxidative compounds (( + )-catechin, Trolox, trans-ferulic acid, hesperetin, and caffeic acid) in solution and in powder as blind duplicates. A statistical treatment revealed that the relative standard deviation of repeatability (RSDr) of material solutions ranged from 5.9% to 13.2%, and from 5.4 to 10.4% in powder sample. The interlaboratory relative standard deviation of reproducibility (RSDR) of material solutions or powders ranged from 16.2% to 61.4%, from 16.9% to 33.2%, respectively. The HorRat values of material solutions or powders calculated from the highest concentration of Trolox standard carve (50μM) ranged from 1.48 to 5.62 in solution example, from 1.54 to 3.03 in powder example, respectively. Thus, it is difficult to conclude that H-ORAC method used in the present interlaboratory study has acceptable precision. It is suggested that the individualities of plate readers cause the differences in the change of fluorescence intensity among the wells of the microplate, and that reduction of such differences induces improvement in the reproducibility.
