Browsing by Author "Speisky, Hernan"

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    Amplification of the antioxidant properties of myricetin, fisetin, and morin following their oxidation
    (2024) Arias-Sante, M. Fernanda; Fuentes, Jocelyn; Ojeda, Camila; Aranda, Mario; Pastene, Edgar; Speisky, Hernan
    Quercetin oxidation leads to the formation of a metabolite, 2-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxy-3(2H)benzofuranone, whose antioxidant potency was recently reported to be a 1000-fold higher than that of its precursor. The formation of similar metabolites (BZF) is limited to certain flavonols (FL), among which are myricetin, fisetin, and morin. Here we addressed the consequences of inducing the auto-oxidation of these flavonols in terms of their antioxidant properties (assessed in ROS-exposed Caco-2 cells). The mixtures that result from their oxidation (FLox) exhibited antioxidant activities 10-to-50-fold higher than those of their precursors. Such amplification was fully attributable to the presence of BZF in each FLox (established by HPLC-ESI-MS/MS and chemical subtraction techniques). An identical amplification was also found when the antioxidant activities of BZF, isolated from each FLox, and FL were compared. These findings warrant the search of these BZF in edible plants and their subsequent evaluation as a new type of functional food ingredients.
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    Evaluation of the antioxidant capacity of food samples: a chemical examination of the oxygen radical absorbance capacity assay
    (WILEY-BLACKWELL, 2018) Dorta Pérez, Eva; Fuentes Lemus, Eduardo Felipe; Speisky, Hernan; Lissi Gervaso, Eduardo A.; López Alarcón, Camilo Ignacio; Apak, Resat; Capanoglu, Esra; Shahidi, Fereidoon
    This chapter describes, from a critical point of view, the main in vitro methodologies employed to assess the antioxidant capacity (AC) of food samples. Considering the wide use of the oxygen radical absorbance capacity (ORAC) assay, it presents a chemical examination of this methodology. The methods for AC evaluation are based on different strategies; these include the use of colored and stable free radicals, evaluation of the capacity of antioxidants to reduce cupric or ferric ions, estimation of the ability of phenolic compounds (PC) to protect a target molecule exposed to a free radical source, and evaluation of the capacity of PC to form nanoparticles. When the antioxidant activity of a particular sample is evaluated, it is recommended to know the meanings and limitations of the assays being employed. In the case of the ORAC assay, the nature of the free radicals generated during the thermolysis of AAPH should also be considered.
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    Time-dependence of Ferric Reducing Antioxidant Power (FRAP) index in Chilean apples and berries
    (ARCHIVOS LATINOAMERICANOS NUTRICION, 2011) Henriquez, Carolina; Lopez Alarcon, Camilo; Gomez, Maritza; Lutz, Mariane; Speisky, Hernan
    We hypothesize that the Ferric Reducing Antioxidant Power (FRAP) assay that follows the reaction of Fe3+-TPTZ at 593 nm underestimates the antioxidant capacity of fruits, since the standardized time of the reaction (4 min) is not enough to titrate all the reducing compounds available. We measured FRAP, total phenolics and anthocyanins content in a variety of Chilean berry fruits (blueberries, blackberries, raspberries and strawberries) and apples (cv. Fuji, Granny Smith, Pink Lady, Red Delicious and Royal Gala). Taking into account the dependence of FRAP on the time course of the reaction, we propose to measure FRAP indexes after 1 min (FRAP-1), 30 min (FRAP-30) and 120 min (FRAP-120) of incubation. Most fruit extracts showed significant correlations between the antioxidant capacity and the incubation time, although in some cases the FRAP indexes did not correlate with the total phenolics and/or anthocyanins content. In fact, in apples and berries the correlation between anthocyanins content and FRAP indexes decreased with the incubation time. It is concluded that the fruit extracts analyzed require an incubation period higher than the established in the original experimental protocol to reach the equilibrium, due to the presence of a complex mixture of antioxidant compounds. In addition, a kinetic profile should be realized in each sample studied to establish the most suitable incubation period to titrate all the reactive antioxidant species.