Effect of dispersed phase crystallization on aroma release from oil-in-water emulsions

The release of volatile aroma compounds before or during food consumption is one of the key factors in perception of food quality. Volatile aroma release from food emulsions is governed by both thermodynamics of binding of aroma molecules to different food constituents and the kinetics of its transport within different regions of food. Lipids, being a large reservoir of aroma compounds, significantly influence aroma release from food emulsions and these effects have been well documented. However, most of these studies involve liquid lipid and effects of fat crystallization on the aroma release properties have been largely ignored.; The major difficulty faced in the comparison of the interactions of aroma compounds with solid and with liquid fats is that there is always a temperature or composition change required to initiate crystallization which might itself affect the binding properties of the system. However, by varying the temperature history of an emulsified lipid it was possible to compare aroma interactions of supercooled liquid droplets with those of crystalline droplets at the same temperature and with the same composition.; The first objective of this study was to understand the thermodynamics of aroma-solid fat interaction in oil-in-water emulsions. The partitioning of a mixture of aroma compounds (ethyl butanoate, ethyl pentanoate, ethyl heptanoate and ethyl octanoate) to model n-eicosane-in-water emulsions stabilized with sodium caseinate was studied by static headspace gas chromatography. The binding of aroma compounds by the liquid droplets was modeled in terms of the bulk oil-gas and water-gas partition coefficients and the volume fraction of the phases. However, aroma binding by solid droplets depended on the specific surface area of the droplets suggesting a surface-binding mechanism and an effective surface binding coefficient was defined for each aroma compounds as the ratio of aqueous to interfacial concentration. This value was constant up to a critical point after which it increased dramatically as the droplets bound much more volatiles. The increase coincided with an apparent dissolution of the solid droplets in the adsorbed volatile (as measured by a decrease in the measured melting enthalpy). Using the surface binding coefficient and bulk partition coefficients it was possible to model the aroma binding by solid droplets in emulsion.; The results from eicosane emulsion were also compared with triglyceride emulsions prepared with hydrogenated palm stearin (HPS) and Salatrim RTM (Short And Long chain Acyl TRIglyceride Molecules). For all aroma compounds, equilibrium aroma release from solid droplet emulsions was significantly higher than that for liquid droplet emulsions. It was found that while the partitioning of volatile aroma compounds from emulsion does not depend on the type of liquid oil used, the interactions between solid fat droplets and aroma compounds are significantly influenced by the nature of the crystalline fat. Notably, partitioning into the headspace was much lower for emulsions with solid triglyceride droplets than that for solid alkane droplets.; The second objective of this work was to investigate the kinetics of aroma release from solid fat and liquid oil in emulsion droplets. Emulsions (eicosane or HPS) were mixed with a mixture of aroma compounds and transferred to a model mouth. The glass vessel was sealed and the emulsion was allowed 15 s for the aroma compounds to release into the headspace before a nitrogen flow was used to sweep the headspace out of the container and into a mass spectrometer detector. The change in aroma concentration in the headspace was plotted with time and it was found that with the start of gas flow the aroma concentration increases sharply to a maximum value and thereafter decreases as the rate that aroma compounds are swept out of the glass vessel is exceeded by the rate at which it is released into the gas phase by the emulsion. The rate of release...