Influence of Temperature on the Distribution of Catechin in Corn Oil-in-Water Emulsions and Some Relevant Thermodynamic Parameters
2014
Martínez-Aranda, Nuria | Losada-Barreiro, Sonia | Bravo Diaz, Carlos | Romsted, Laurence S.
We investigated the effects of increasing temperature and emulsifier volume fraction (ΦI) on the distribution of catechin (CAT) in stripped corn oil-in-water emulsions. We also estimated relevant thermodynamic parameters for the transfer of CAT from the aqueous to the interfacial region because CAT is sparingly soluble in corn oil and mainly distributes between the aqueous and interfacial regions of emulsions. The distribution of CAT was assessed in the intact emulsions by employing a well-established kinetic method based on the reaction between a hydrophobic arenediazonium ion and CAT. Results are interpreted on the basis of the pseudophase kinetic model, which provides estimates of the second order interfacial rate constant, kI, and the partition constant PWᴵbetween the aqueous and interfacial region of the emulsion from kₒbₛversus ΦIprofiles. The PWᴵvalues are quite high, increasing from 188 (T = 15 °C) to 368 (T = 25 °C). This change in PWᴵreflects the dependence of the percentage of CAT in the interfacial region, %CATI, on temperature. At T = 15 °C and ΦI= 0.005, %CATI≈ 60. This percentage increases upon increasing ΦIto %CATI≈ 88 at ΦI= 0.04. An increase in T from 15 to 25 °C promotes incorporation of CAT into the interfacial region so that at ΦI= 0.005, %CATIincreases from ~60 to ~85. The thermodynamic parameters for the transfer from the aqueous to the interfacial region (ΔG⁰,ᵂ → ᴵ, (ΔH⁰,ᵂ → ᴵand (ΔS⁰,ᵂ → ᴵ) were obtained from the PWᴵvalues at a series of temperatures by the van’t Hoff method and the Gibbs equation, respectively. ΔG⁰,ᵂ → ᴵis negative at any temperature, indicating that the transfer of CAT from the aqueous to the interfacial region is an spontaneous process.
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