A Fluorometric Assay to Determine Antioxidant Activity of Both Hydrophilic and Lipophilic Components in Plant Foods

We established a fluorometric method to determine total antioxidant activity of plant foods, green leafy vegetables and beans, after extracting [1] hydrophilic components (H) with acidified methanol (methanol:glacial acetatic acid:water = 50:3.7:46.3), [2] lipophilic components (L) with methanol followed by tetrahydrofuran (THF), or [3] both H + L using sequential extraction of acidified methanol and THF together. Both the hydrophilic assay (using a hydrophilic radical initiator, AAPH,10 mmol/L, and hydrophilic probe, DCFH, 2 μmol/L), and the lipophilic assay (using a lipophilic radical initiator, MeO‐AMVN, 2 mmol/L, and the lipophilic probe, BODIPY, 2 μmol/L) were used to measure antioxidant activity. The inhibition of BODIPY oxidation was significantly increased (p< 0.01) when both H + L were extracted using acidified methanol and organic solvent as compared to those extracted by organic solvent alone. In addition, the rate of DCFH oxidation was significantly delayed (p<0.05) when both components were present as compared to the H alone. The combination of H + L in these plant foods showed significantly greater antioxidant activity than that of either H or L alone. Thus, both H & L in plant foods and their interactions should be considered when determining antioxidant activity of plant foods. [Supported in part by USDA #58‐1950‐7‐707 USA & BioGreen 21 Program (Code #20070301034009) RDA, Korea]