Fluphenazine hydrochloride radical cation assay: a new, rapid and precise method to determine in vitro total antioxidant capacity of fruit extracts

A new procedure based on generation and subsequent reduction of orange-colored fluphenazine hydrochloride radical (FPH ⁺) is presented for the screening of total antioxidant capacity (TAC) of various fruit matrices. The FPH ⁺ was obtained by mixing fluphenazine hydrochloride with persulfate (final concentration 2 mmol/L and 0.05 mmol/L, respectively) in 3 mol/L H ₂SO ₄ with constant shaking for 5 min. The solution formed showed maximum absorption as 0.8 ± 0.02 at 500 nm in first-order derivative spectrum. The percent inhibition of the solution increased linearly on addition of increasing amounts of standard antioxidants i.e., ascorbic acid etc. The TACs of sample citrus juices were calculated in terms of ascorbic acid equivalents (AAEs) by comparing their inhibition curves with that of ascorbic acid. Comparison of AAE values of different commercial orange juices using the newly developed FPH ⁺ assay and the well-known ABTS/K ₂S ₂O ₈ and DMPD/FeCl ₃ assays indicated the precision and comparable sensitivity of the method. The proposed procedure is quick, economical, and more precise and gives results comparable to contemporary assays.