Solubility of Gallic Acid, Catechin, and Protocatechuic Acid in Subcritical Water from (298.75 to 415.85) K

Journal of Chemical & Engineering Data (Impact Factor: 2). 06/2010; 55(9):3101-3108. DOI:10.1021/je901097n

ABSTRACT The solubility of gallic acid hydrate, protocatechuic acid, and (+)-catechin hydrate was measured between 298.75 K and 415.85 K using a dynamic flow apparatus. The aqueous solubility of gallic acid hydrate was found to vary between 12.6 g·L−1 at 298.75 K and 2870 g·L−1 at 415.85 K. The aqueous solubility of protocatechuic acid at the same temperatures varied between 29.4 g·L−1 and 1180 g·L−1, respectively, while that of (+)-catechin hydrate varied between 2.26 g·L−1 and 576 g·L−1, respectively. The aqueous solubility of the phenolic compounds was found to increase exponentially with temperature. The temperature dependence of the aqueous solubility of the phenolic compounds was estimated using empirical correlations based on the data presented in this work. The thermodynamic properties such as standard molar enthalpy, standard molar entropy, and standard molar Gibbs energy of solution were also calculated from the solubility data.

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    ABSTRACT: The effects of temperature (50 to 200 °C) and contact time (5 to 30 min) on the pressurized hot water extraction of deodorised thyme were explored for antioxidant activity, polyphenol profiles and total antioxidants. Six not previously reported polyphenolic compounds were identified in thyme. An inverse correlation was found between the antioxidant activity and total antioxidants with the amount and diversity of polyphenols. The highest total extract yield and antioxidant activity was obtained at 200 °C, although maximum polyphenol extraction yields of hydroxycinnamic acids, flavones, flavonols/flavanones and total polyphenols were detected at 100ºC and 5 min. Higher temperatures and longer exposure times reduced extract polyphenol diversity. Dihydroxyphenyllactic acid was the only phenolic compound whose extraction yield increased with temperature, probably as a product of the thermal degradation of rosmarinic acid. Consequently, for extracting phenolics from thyme 100ºC and 5 min would be appropriate operating conditions, whereas antioxidant-active non-phenolic compounds were favoured at higher temperatures and exposure times.
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Sep 24, 2013