Abstract
The Briggs-Rauscher (BR) reaction is free radical based where the kinetics of formation of different iodide species leads to potentiometric and color oscillations. These oscillations were monitored in this study using a UV/Vis attenuated total reflection probe to develop an assay to measure the antioxidant content in complex matrices. The periodicity of the BR reaction was found to be very consistent (range 24-25 seconds, n = 16). Adding various amounts of ascorbic acid, a well-known antioxidant, led to an inhibition of the reaction with a linear calibration curve of antioxidant periodicity time (APT, r 2 > 0.99). The validity of this test in complex matrices was studied by determining the APT of nine fruits, and the resulting antioxidant capacity in ascorbic acid equivalency was calculated. The results generated by this assay were found be accurate through comparison with the well-established FRAP assay. These results show that visual or spectrometric monitoring of BR reaction can be used as a reliable, quick, and inexpensive alternative to more established assays with the added advantage that values generated from this assay is at pH 2 which is similar to that in the human stomach.
Highlights
Antioxidants have been widely proven to show beneficial effects on the human body.[1–3] the accurate, quick and cheap determination of antioxidants present in complex naturally occurring matrices, such as fruits and vegetables, has been an area of continued focus
A new approach based on synthetized MnO2 nanosheets to determine antioxidant levels was proposed as recently as earlier in 2020.[4]. There are three main challenges to determine antioxidant present in food and nutraceuticals: a) there is huge chemical diversity of antioxidants, so any test must account for different chemical structures that contribute to antioxidant properties of that particular food group; b) the matrices of foods are a complex mixture of cellulosic material, lignin, vitamins, phytochemicals, etc. so interference from these water-soluble materials is an issue during measurements; and c) antioxidants are intrinsically unstable due to their rapid oxidation, the test must be quick and simple, if being conducted in an agricultural setting
3.1 Blank BR Reaction and Effect of Antioxidant Freshly mixed BR reaction reagents resulted in clear solution as shown in Fig. 1 and over the 10–15 seconds the clear solution slowly turned to amber color and abruptly changed to blue color
Summary
Antioxidants have been widely proven to show beneficial effects on the human body.[1–3] the accurate, quick and cheap determination of antioxidants present in complex naturally occurring matrices, such as fruits and vegetables, has been an area of continued focus. ORAC (oxygen radical absorbance capacity) uses peroxy radical generated using fluorescein as a probe while FRAP (ferric reducing antioxidant power) is based on the reduction of an Fe(iii) to Fe(ii) ion using ferricyanide as a probe Both these tests are commercially available as kits but are expensive and may be out of reach for many parts of the world. In this study, the feasibility of using color change in BR reaction is studied as a possible approach to determine antioxidant content in complex matrices If successful, this will develop a new assay that is cheap and easy to do, it is implementable in all educational settings ( at high schools as needed) to show the beauty of applying a simple reaction to solve a complicated problem and help energize students to aspire to study chemistry
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