In vitro measurement of volatile release in model lipid emulsions using proton transfer reaction mass spectrometry.

The presence of fat in food plays an important role in the way aroma is released during consumption and in the creation of the overall sensory impression. Fat acts as a reservoir for lipophilic volatile compounds and modulates the timing and delivery of aroma compounds in a unique manner. Despite considerable research, reproducible in vitro methods for measuring the effect of fat on volatile release are lacking. An open in vitro cell was used to simulate the open human naso-oropharygeal system and was interfaced with a proton transfer reaction mass spectrometer (PTR-MS) to examine some of the fundamental effects of fat on dynamic volatile release in liquid fat emulsions. Lipid emulsions with various fat contents (0-20%) and droplet sizes (0.25, 0.5, and 5.0 μM) were spiked with flavor volatiles representing a range of lipophilicity (K(o/w) = 1-1380). Preloaded syringes of spiked emulsion were injected into the cell, and temporal changes in release were measured under dynamic conditions. Significant differences in release curves were measured according to the lipid content of emulsions, the vapor pressure, and K(o/w) values of the volatile compounds. With increasing addition of fat, the critical volatile release parameters, maximum concentration (I(max)), time to maximum concentration (T(max)), and the integrated area under the concentration curve (AUC), were affected. The in vitro curves were reproducible and in agreement with theory and correlated with the preswallow phase of in vivo release data. An exponential model was used to calculate changes in mass transfer rates with increased fat addition.