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Review
. 2020 Aug 5;9(8):709.
doi: 10.3390/antiox9080709.

The Versatility of Antioxidant Assays in Food Science and Safety-Chemistry, Applications, Strengths, and Limitations

Nabeelah Bibi Sadeer  1 , Domenico Montesano  2 , Stefania Albrizio  3   4 , Gokhan Zengin  5 , Mohamad Fawzi Mahomoodally  1
Affiliations
Review

The Versatility of Antioxidant Assays in Food Science and Safety-Chemistry, Applications, Strengths, and Limitations

Nabeelah Bibi Sadeer et al. Antioxidants (Basel). .

Abstract

Currently, there is a growing interest in screening and quantifying antioxidants from biological samples in the quest for natural and effective antioxidants to combat free radical-related pathological complications. Antioxidant assays play a crucial role in high-throughput and cost-effective assessment of antioxidant capacities of natural products such as medicinal plants and food samples. However, several investigators have expressed concerns about the reliability of existing in vitro assays. Such concerns arise mainly from the poor correlation between in vitro and in vivo results. In addition, in vitro assays have the problem of reproducibility. To date, antioxidant capacities are measured using a panel of assays whereby each assay has its own advantages and limitations. This unparalleled review hotly disputes on in vitro antioxidant assays and elaborates on the chemistry behind each assay with the aim to point out respective principles/concepts. The following critical questions are also addressed: (1) What make antioxidant assays coloured? (2) What is the reason for working at a particular wavelength? (3) What are the advantages and limitations of each assay? and (4) Why is a particular colour observed in antioxidant-oxidant chemical reactions? Furthermore, this review details the chemical mechanism of reactions that occur in each assay together with a colour ribbon to illustrate changes in colour. The review ends with a critical conclusion on existing assays and suggests constructive improvements on how to develop an adequate and universal antioxidant assay.

Keywords: antioxidants; chemical reactions; colorimetry; free radicals; limitations; oxidative stress; spectrophotometer.

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Conflict of interest statement

All the authors declare that there is no conflict of interest.

Figures

Figure 1
Figure 1
Colour wheel.
Figure 2
Figure 2
Folin–Ciocalteu (F–C) assay.
Figure 3
Figure 3
2,2-diphenyl-1-picrylhydrazyl (DPPH) reaction mechanism.
Figure 4
Figure 4
2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) reaction mechanism.
Figure 5
Figure 5
HO• reaction mechanism.
Figure 6
Figure 6
Steps involved in the lipid oxidation and antioxidant action in the TBARS activity assay.
Figure 7
Figure 7
NO• reaction mechanism.
Figure 8
Figure 8
ONOO− reaction mechanism.
Figure 9
Figure 9
O2•− reaction mechanism.
Figure 10
Figure 10
H2O2 reaction mechanism.
Figure 11
Figure 11
Ferric reducing antioxidant power (FRAP) reaction mechanism.
Figure 12
Figure 12
Cupric reducing antioxidant capacity (CUPRAC) reaction mechanism.
Figure 13
Figure 13
Fe (II) complexes have six electrons in the 5-d orbitals. In the absence of a crystal field (ligands), the orbitals are degenerate. In the presence of ligands (CN−), the d-orbitals split into eg and t2g orbitals with an energy difference of ∆O.
Figure 14
Figure 14
Potassium ferricyanide reaction mechanism.
Figure 15
Figure 15
Phosphomolybdenum reaction mechanism.
Figure 16
Figure 16
Metal chelating reaction mechanism.
Figure 17
Figure 17
Cut-off effect of antioxidant activity with respect to polarity (Adapted from Shahidi and Zhong [109]).
Figure 18
Figure 18
β-carotene reaction mechanism.
Figure 18
Figure 18
β-carotene reaction mechanism.
Figure 19
Figure 19
Flowchart with proposed steps to follow in order to develop a universal antioxidant assay.
See this image and copyright information in PMC

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