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  • br Conflict of interest br Acknowledgments This work was fin

    2024-07-11


    Conflict of interest
    Acknowledgments This work was financially supported by the Fund Project of Sichuan Provincial Department of Education (16ZB0053), the Scientific Research Foundation of Sichuan Agricultural University (No. 06021400) and the China Postdoctoral Science Foundation (No. 2015M580795 and 2016M602605).
    Introduction Such a plethora of data on the antioxidant activities of a large variety of food preparations naturally raises the question of comparing their effectiveness with general, common standards. This is a difficult task, frequently eluded by many reports that simply ascribe particular values of antioxidant activity to complex mixtures, without any concern for the origin of such an activity or of their site of action. An example of such a simplification is the frequent use of 1,1-diphenyl-2-picrylhydrazyl (DPPH) (Prior, Wu, & Schaich, 2005), the ferric-ion reducing antioxidant power (FRAP) (Ryan & Prescott, 2010), or Trolox Equivalent Antioxidant Capacity (TEAC) (Muñoz-Acevedo et al., 2011, Prior et al., 2005, Sproston and Akoh, 2016) methodologies, the latter being based on a barely water-soluble compound, and applied to heterogeneous mixtures, such as micelles or emulsions (González-Hidalgo et al., 2012, Sólyom et al., 2014). Frankel’s conclusion that “there cannot be a simple and rapid method to evaluate antioxidants in complex foods and biological systems” (Frankel, 2001), or Niki’s critical reflections on how correctly we are measuring antioxidant activities (Niki, 2002), have been ignored in the past fifteen years by a large portion of food chemists. The latter’s observations that “the antioxidant efficacy depends markedly on the type of oxidant” and that “the efficacy of radical scavenging depends on the localization of the antioxidant” have found support, with time, from other research groups. It is now increasingly accepted that the antioxidant activity of a particular lcz696 in a micro-heterogeneous environment depends on the distribution of the antioxidant and of the measuring probe in such a medium (Aliaga et al., 2009, Bridi et al., 2011, Galan et al., 2016, Kiralan et al., 2014). This is the reason why different orders of effectiveness are obtained for the same series of compounds, even when the same methods of antioxidant evaluation are employed by a research group (Alemán et al., 2015, Aliaga et al., 2008). Thus, groups concerned with the antioxidant effectiveness of food preparations have been increasingly conscious of the need to determine the site of action of AOs in these heterogeneous mixtures (Costa et al., 2015, Losada-Barreiro et al., 2015). In doing so, subtle effects of the distribution, structure and orientation of these antioxidants and/or their evaluating probes on the measured effectiveness have been detected (Aliaga et al., 2016). One of them, the amphiphobic nature of radical probes, or of phenolic antioxidants, has been invoked to rationalize the long known paradoxical or “cut-off” effect of many of these compounds in food mixtures. By using the series of probes 1a–f, derived from lcz696 the nitroxyl TEMPO radical, their cut-off effect vis-à-vis various antioxidants has been rationalized in micellar solutions (Aliaga, Lopez de Arbina, & Rezende, 2016) and food emulsions (Lopez de Arbina, Rezende, & Aliaga, 2017). In spite of possessing the same nitroxyl fragment, these radicals are quenched differently by a given antioxidant through a hydrogen-abstracting process in a micro-heterogeneous medium, depending on the size of the 4-alkanoyl chain. Irrespective of the evaluated antioxidant, “cut-off” patterns are observed in plots of Relative Antioxidant Effectiveness vs. chain-size, with extreme values detected for probes with an intermediate chain-size, or hydrophobicity. In the present communication we show that this paradoxical response can be used to determine the location and site of action of an antioxidant in a micellar system or an emulsion, if its reactivity towards radicals 1a–f is compared for various members of the probe series.