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

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.

Approach to Optimization of FRAP Methodology for Studies Based on Selected Monoterpenes

“…Detailed analysis of the obtained results revealed some structure–antioxidant activity relationships related to certain antioxidant mechanisms. In accordance with Sadeer et al [ 16 ], FRAP is based on an electron transfer mechanism in which aryloxyl radicals are formed. In the presented studies, the highest reduction activity was observed for cyclic hydrocarbon terpenes with conjugated double bonds without single electron transfer (SET) moiety characteristics (with the exception of γ-terpinene without the moiety) ( Figure 3 ).…”

Phytochemical Profile and Biological Activities of Crude and Purified Leonurus cardiaca Extracts

“…For example, in the Folin–Ciocalteu method, the reagent could be reduced by not only phenolics but also non-phenolics (peptides etc. ), and thus the obtained results might not be reliable [ 24 , 25 ]. In this sense, advanced chromatographic techniques are helpful to provide certain information regarding the chemical profiles of plant extracts.…”

Common Trends and Differences in Antioxidant Activity Analysis of Phenolic Substances Using Single Electron Transfer Based Assays

“…Each of these assays has unique properties and limitations, making it difficult to compare results generated using different methods—for example, measurement at a fixed time or kinetic, measurement of different concentrations or only one concentration, and the use of different solvents [ 23 , 24 , 25 , 26 ]. Furthermore, the outcome of the assays can be evaluated in different ways, resulting in metrics, such as half maximal effective concentration (EC 50 ), time to reach the EC 50 (T EC 50 ), antiradical efficiency, antiradical power (ARP), stoichiometry, kinetic behavior and rate constant, radical scavenging activity, or trolox equivalent antioxidant capacity (TEAC) [ 23 , 24 , 27 , 28 , 29 , 30 , 31 , 32 ].…”