Determination of Total Antioxidant Capacity Using Thiamine as a Natural Fluorescent Probe

Woodland Oliveira,Josué Santos

doi:10.21577/0103-5053.20200123

Abstract

This work proposes a spectrofluorometric method for the determination of total antioxidant capacity (CAO) in beverage samples, based on inhibition of thiochrome formation (λex = 370 nm, λem = 440 nm); a product of thiamine (vitamin B1) oxidation from K3Fe(CN)6. In the development of the method, gallic acid (GA) was used as a reference, and inhibition of thiochrome formation (in percentage) was used as the analytical response. The selectivity of the method was evaluated using seven different compounds (gallic acid, ascorbic acid, quercetin, butylhydroxytoluene (BHT), 6-hydroxy-2,5,7,8-tetramethylchroman-2 (Trolox), cysteine, and glucose). As proof of concept, the proposed method was applied in the determination of CAO in different samples, such as teas and infusions, red wines, and white wines. The results were compared with the Folin-Ciocalteu (FC), 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS•+), and 2,2-diphenyl-1-picrylhydrazyl (DPPH•) methods using the linear correlation between the methods (at 95% confidence). We observed excellent agreement between the proposed method and FC (correlation coefficient (r) = 0.9768) and ABTS•+ (r = 0.9842), compared with DPPH• method (r = 0.8502). For the determination of total CAO in beverages, the proposed method developed proved to be fast, sensitive, simple, and the results were in agreement with established assays.

Highlights

The consumption of foods rich in antioxidant compounds such as vitamins, carotenoids, and phenolic compounds has been associated with the prevention of the diseases related to oxidative stress
The present work proposes to develop a simple, rapid, and sensitive analytical methodology for the determination of total antioxidant capacity, based on thiamine oxidation inhibition. This method is based on a reduction of thiochrome formation and a consequent decrease in the analytical signal, which is proportional to the concentration of the antioxidant
The ability of different FeIII complexes to oxidize thiamine to thiochrome was evaluated under physiological conditions

Summary

Introduction

The consumption of foods rich in antioxidant compounds such as vitamins, carotenoids, and phenolic compounds has been associated with the prevention of the diseases related to oxidative stress. The present work proposes to develop a simple, rapid, and sensitive analytical methodology for the determination of total antioxidant capacity, based on thiamine oxidation inhibition. This method is based on a reduction of thiochrome formation and a consequent decrease in the analytical signal, which is proportional to the concentration of the antioxidant. The analytical reference signals were obtained from solutions analogous to those of the methods being applied by replacing the volume of the solution of the standard or the sample with deionized water. The analytical reference signal was obtained from a solution similar to the previous one, where the sample volume was replaced by deionized water. A normal distribution of the data (random error) and a confidence interval of 95% were considered

Results and Discussion

Evaluation of the buffer solution concentration

Evaluation of reagent concentrations

Conclusions