Antioxidant activity and calcium binding of isomeric hydroxybenzoates
The association constant for calcium binding to hydroxybenzoates in aqueous 0.16 M NaCl at 25 °C was found electrochemically to have the value K ass = 280 mol L −1 with ΔH o = −51 kJ mol −1 , ΔS o = −122 J mol −1 K −1 for the 2-isomer (salicylate), K ass = 7 mol L −1 with ΔH o = −39 kJ mol −1 , ΔS o = −116 J mol −1 K −1 for the 3-isomer, and K ass = 8 mol L −1 with ΔH o = −51 kJ mol −1 , ΔS o = −155 J mol −1 K −1 for the 4-isomer. The 3- and 4-isomers were found more efficient as antioxidants than the 2-isomer in decreasing oxygen consumption rate in a peroxidating methyl linoleate emulsion and less sensitive to presence of calcium. All isomers were found prooxidative for iron-catalyzed initiation of oxidation due to enhanced radical formation as shown by electron spin resonance spectroscopy. Calcium salicylate was found to have low solubility with a solubility product K sp = 4.49·10 −6 based on activity with ΔH o = 67 kJ mol −1 , ΔS o = 123 J mol −1 K −1 for dissolution in water, when corrected for the strong complex formation. Calcium in food and beverages may thus lower antioxidant activity of plant phenols through complexation or by precipitation. © 2017
Zhao, Z.; Vavrusova, M.; and Skibsted, L.H.
"Antioxidant activity and calcium binding of isomeric hydroxybenzoates,"
Journal of Food and Drug Analysis: Vol. 26
, Article 51.
Available at: https://doi.org/10.1016/j.jfda.2017.07.001
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