Abstract
The 2,2′-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay is a valid and commonly test used to measure the total antioxidant capacity in natural extracts. The results of this assay are frequently expressed as IC50 values. Nevertheless, the reported IC50 value is influenced by the concentration of the DPPH solution used in the methodology. Consequently, the aim of this study was to determine an IC50 value free of the influence of the DPPH concentration to evaluate correctly the antioxidant capacity of natural compounds. We have established a standardized unit for the antioxidant concentration (ng antioxidant agent/ nmol DPPH) in the concentration–response curves. Then, these curves were used to calculate the IC50 values. The natural antioxidants assessed in this study were ascorbic acid, quercetin and an ethanolic extract of Justicia spicigera. The IC50 values were estimated from nonlinear and linear regression analyses. The use of standardized units resulted in similar curves and IC50 values for the same natural antioxidant (P values from 0.0931 to 0.5512), under different concentrations of the DPPH radical. The lack of usage of standardized units resulted in different curves and IC50 values (P values from 0.0002 to 0.0022). In conclusion, our practical standardization provides a correct interpretation of the antioxidant capacities of natural products under the DPPH scavenging assay.
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This study was financially supported by the Universidad Autónoma de San Luis Potosí—Fondo de Apoyo a la Investigación (Grant Number C19-FAI-05-54.54) and the Consejo Nacional de Ciencia y Tecnologia (CONACyT)—CienciaBásica (Grant Number CB-2015-01-257872).
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OHA-M contributed to the study conception and design. Material preparation, data collection and analysis were performed by FMM, AJAC, JRZM and CCÁ. The first draft of the manuscript was written by OHA-M. All authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.
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Martinez-Morales, F., Alonso-Castro, A.J., Zapata-Morales, J.R. et al. Use of standardized units for a correct interpretation of IC50 values obtained from the inhibition of the DPPH radical by natural antioxidants. Chem. Pap. 74, 3325–3334 (2020). https://doi.org/10.1007/s11696-020-01161-x
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DOI: https://doi.org/10.1007/s11696-020-01161-x