Aroma compounds dynamic headspace method

The primary interference with this basis of isolation is the water present in a sample. In most foods, the aroma components seldom make up more than 300 ppm (0.03%) of the product. Yet, the moisture content of a food, even a dry food, is generally above 2% and thus isolation methods based solely on volatility will produce a dilute solution of aroma componnds in water. The high boihng point of water precludes a simple concentration and analysis, i.e., the aroma compounds would be lost during concentration since they are present in low concentrations and are often more volatile than water. Thus, most dynamic headspace methods of aroma isolation involve some additional method to remove water from the isolate. 

A consideration of volatility as a means of aroma isolation requires an appreciation for the factors that influence the amount (or proportion) of an aroma compound in the gaseous phase vs. in the food at equilibrium (static headspace isolation methods) and nonequiUbrium conditions (dynamic headspace isolation methods). In both cases, our methodology requires that the aroma compound partitions into the gas phase for isolation. Considering equilibrium conditions first, the amount of an aroma compound in the gaseous phase is defined by the gas food partition coefficient (kg,). This can be most simply expressed as ... 

A nonequilibrium isolation method (e.g., dynamic headspace) depends upon many of the same factors as the equilibrium method discussed above, and thus also poorly represents what is found in the food. However, additional considerations must be made for the nonequilibrium nature of the method. In nonequilibrium situations, the rate of release of aroma compounds from a food into a gas phase has to be considered. In this method, one may pass a gas stream through a food with the gas stream picking up aroma compounds under nonequilibrium conditions. The aroma compounds would be subsequently stripped from the gas stream to produce an aroma isolate. 

Analytical methods involving exhaustive extraction of flavor compounds (i.e., liquid/liquid extraction, dynamic headspace) do not take these matrix effects into account. However, new instrumentation and methodologies are yielding improved information on the mechanisms involved in flavor/matrix interactions and the effects on flavor perception. For example, spectroscopic techniques, such as nuclear magnetic resonance (NMR), can provide information on complex formation as a function of chemical environment and have been used to study both intra- and intermolecular interactions in model systems [28,31]. In addition, NMR techniques, initially developed to study ligand binding for biological and pharmaceutical applications, were applied in 2002 to model food systems to screen flavor mixtures and identify those compounds that will bind to macromolecules such as proteins and tannins [32]. Flavor release in the mouth can be simulated with analytical tools such as the retronasal aroma simulator (RAS) developed by Roberts and Acree [33]. These release cells can provide... 

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