Influence of temperature on the distribution of catechin in corn oil-in water emulsions and some relevant thermodynamic parameters

We investigated the effects of increasing temperature and emulsifier volume fraction (Φ_I) 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, k_I, and the partition constant P_W^I between the aqueous and interfacial region of the emulsion from k_obs versus Φ_I profiles. The P_W^I values are quite high, increasing from 188 (T = 15 °C) to 368 (T = 25 °C). This change in P_W^I reflects the dependence of the percentage of CAT in the interfacial region, %CAT_I, on temperature. At T = 15 °C and Φ_I = 0.005, %CAT_I ≈ 60. This percentage increases upon increasing Φ_I to %CAT_I ≈ 88 at Φ_I = 0.04. An increase in T from 15 to 25 °C promotes incorporation of CAT into the interfacial region so that at Φ_I = 0.005, %CAT_I increases from ~60 to ~85. The thermodynamic parameters for the transfer from the aqueous to the interfacial region (ΔG^{0,W → I}, (ΔH^{0,W → I} and (ΔS^{0,W → I}) were obtained from the P_W^I values at a series of temperatures by the van’t Hoff method and the Gibbs equation, respectively. ΔG^{0,W → I} is negative at any temperature, indicating that the transfer of CAT from the aqueous to the interfacial region is an spontaneous process.