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.

Graphic abstract

中文翻译：

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使用标准化单位正确解释由天然抗氧化剂抑制DPPH自由基获得的IC50值

摘要

2,2'-二苯基-1-吡啶并肼基（DPPH）自由基清除测定法是一种有效的常用测试方法，用于测量天然提取物中的总抗氧化能力。该测定的结果通常表示为IC ₅₀值。但是，报告的IC ₅₀值受该方法中使用的DPPH溶液浓度的影响。因此，本研究的目的是确定不受DPPH浓度影响的IC ₅₀值，以正确评估天然化合物的抗氧化能力。我们在浓度-响应曲线中建立了抗氧化剂浓度的标准化单位（ng抗氧化剂/ nmol DPPH）。然后，这些曲线用于计算IC ₅₀价值观。在这项研究中评估的天然抗氧化剂是抗坏血酸，槲皮素和胡桃木的乙醇提取物。IC ₅₀值是通过非线性和线性回归分析估算的。在DPPH自由基浓度不同的情况下，使用相同的天然抗氧化剂，使用标准化单位可获得相似的曲线和IC ₅₀值（P值为0.0931至0.5512）。缺乏标准化单位的使用导致曲线和IC ₅₀值不同（P值从0.0002到0.0022）。总之，在DPPH清除试验下，我们的实用标准化方法可以正确解释天然产物的抗氧化能力。

图形摘要