Effect of additives on volatility of aroma compounds from dilute aqueous solutions

Volatility of fragrance and flavor substances from food and cosmetic products or intermediates is influenced by admixtures of various nonvolatile substances which occur in these basically aqueous matrices naturally or are added on purpose. For control of the production process and formulation of a final product, it is important to know how such admixtures affect the air-water partitioning of aroma substances. In this work, using an effective headspace gas chromatography method, we studied the effect of salts (NaCl, NaHCO3), saccharides (glucose, sucrose), macrocyclic polysaccharides (α-cyclodextrin, β-cyclodextrin), polyalcohols (ethylene glycol, glycerol) and protein denaturants (urea, guanidine hydrochloride) on the air-water partition coefficient of two isomeric esters ethyl butanoate and butyl ethanoate as typical representatives of aroma substances. The strongest effect was observed for cyclodextrins (aroma retention by inclusion complexation) and for inorganic salts (aroma release by salting-out). For other additives, a weaker salting-in (denaturants, ethylene glycol) or salting-out (saccharides, glycerol) was found. The dependence of these effects on the additive concentration was in all cases well correlated by Setschenow equation and for cyclodextrins also by the 1:1 complex formation model. Determination of the temperature dependence of these effects gave a useful insight into the thermodynamics of the ester-cyclodextrin inclusion binding. Considerations of guest-host size matching supported by simple molecular modeling proved useful to rationalize different binding affinities observed for individual ester-cyclodextrin pairs and suggest their possible binding modes.