Effects of some parameters on DPPH• Scavenging Test and pH on composition and activity in bioactive component extraction and incubation

DPPH stability was evaluated based on light, temperature, solvent and pH of medium with absorbance at 517 nm and UV-Vis spectra. Solvent affects DPPH• stability; degradation was slow at 10-20 ºC and fast at 30-40 ºC. DPPH degradation was better expressed by producing derived absorbances using absorbances between 470-620 nm in spectra. Method showed DPPH as stabile in water and pH 7 and significant increase in degradation in 20-30 ºC. In spectra obtained by absorbance changes during waiting, significant decreases in 510-520 nm and increases in 390-400 nm region were detected. Difference graphs showed DPPH was more stable at low temperatures in water and pH 7. Effect of solvent, buffer concentration and pH on antioxidant-DPPH• interaction was investigated. Studies with 5 antioxidants (gallic acid, Trolox, BHT, catechin, vitamin C), 5 solvents (methanol, water, DMSO, acetone, ethyl acetate) and 3 pHs (2, 7, 10) showed solvent, buffer concentration and pH differences may cause activity increase or decrease. Standard antioxidants and green tea extracts were examined by conventional DPPH, FRAP, Folin, carbonic anhydrase inhibition and on-line HPLC-DAD-FRAP methods to determine antioxidants stability in extraction and storage. pH affected component stability and bioactivity, effect differed on compound basis, and pH 2 resulted in high activity and pH 10 low activity in extracts. Reagent and sample freshness, light, temperature, pH, buffer concentration and solvent affect activity in DPPH• tests. Activity comparison between samples can only be made with results obtained under same conditions.