Method for quantification of antioxidant capacity of processed fruit juices exploring the formation of the Fe(II)/3-hydroxy-4-nitroso-2,7-naphthalenedisulfonic complex

The formation of the Fe(NRS)34- complex was used in a modified spectrophotometric method to quantify the total antioxidant capacity (TAC) of processed fruit juice samples. The procedure is based on the reduction of Fe(III) to Fe(II) in aqueous buffered solution (Tris; pH 8.0) containing the 3-hydroxy-4-nitroso-2,7-naphthalenedisulfonic complex acid (H2NRS). The absorbance values at 730 nm (A730 nm) of the Fe(NRS)34- complex obtained with juice samples were compared with A730 nm values obtained with a standard ascorbic acid solution and then subsequently used to quantify and express the TAC of the samples. Good positive relationship between TAC values in the analysed samples (grape, orange, passion fruit, cashew, peach and strawberry) was found for both Fe(NRS)34- complex (proposed method) and ABTSâ + radical-free method (used as reference method). The TAC values obtained with Fe(NRS)34- and ABTSâ + also showed a positive correlation with the Folin-Ciocalteu index values. Fructose, glucose, BHT and BHA did not interfere in the TAC quantification of the processed fruit juice samples with the proposed method. However, ascorbic acid (natural or added as additive, E300) and its derivatives (E301, E302, E303, E315 and E316) will interfere positively. As a 10-fold dilution is required and the absorbance measurements are performed at 730 nm, the proposed method was not subject to color interference from the tested samples. The procedure suggested here is simple, easy to perform, reproducible, does not use organic solvents and does not need expensive equipment.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author