Analytical Sciences

Method Validation by Interlaboratory Studies of Improved Hydrophilic Oxygen Radical Absorbance Capacity Methods for the Determination of Antioxidant Capacities of Antioxidant Solutions and Food Extracts

Jun WATANABE,*1 Tomoyuki OKI,*2 Jun TAKEBAYASHI,*3 Koji YAMASAKI,*4 Yuko TAKANO-ISHIKAWA,*1 Akihiro HINO,*1 and Akemi YASUI*1

*1 National Food Research Institute, National Agriculture and Food Research Organization, 2-1-12 Kannondai, Tsukuba, Ibaraki 305-8642, Japan
*2 National Agricultural Research Center for Kyushu Okinawa Region, National Agriculture and Food Research Organization, 2421 Suya, Koshi, Kumamoto 861-1192, Japan
*3 National Institute of Health and Nutrition, 1-23-1 Toyama, Shinjuku, Tokyo 162-8636, Japan
*4 Taiyo Kagaku Co., 1-3 Takara, Yokkaichi, Mie 510-0844, Japan

Hydrophilic oxygen radical absorbance capacity (H-ORAC) is a method for evaluating antioxidant capacities of solutions of hydrophilic compounds. In this study, we improved the original method for H-ORAC determination, and evaluated the precision of the two improved methods (methods A and B) by interlaboratory studies using 5 antioxidant solutions and 5 food extracts as test samples. An interlaboratory study of method A, in accordance with the harmonized protocol, demonstrated satisfactory performance (intermediate precision relative standard deviations (RSD_int) ranging from 4.6 to 18.8%; the reproducibility relative standard deviations (RSD_R) ranging from 7.0 to 21.1%, and the HorRat values ranging from 0.40 to 1.93). However, methodological problems remained, and a further improved method, method B, was thus developed. An interlaboratory study of method B by 5 participating laboratories showed better intermediate precision and reproducibility (RSD_int and RSD_R ranging from 1.8 to 9.4%, and from 4.4 to 13.8%, respectively), and all HorRat values for the test samples were less than 1.3, suggesting good performance for the H-ORAC measurement.

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