Flavor unit concept

The critical points and the limitations of the flavor unit concept have been discussed by Rothe (JL2), Frijters (13,) and Meilgaard and Peppard (14). However, these authors agreed that the method can help establish the aroma compounds that contribute significantly to the flavor of a food. 

The composition of the volatile fraction of bread depends on the bread ingredients, the conditions of dough fermentation and the baking process. This fraction contributes significantly to the desirable flavors of the crust and the crumb. For this reason, the volatile fraction of different bread types has been studied by several authors. Within the more than 280 compounds that have been identified in the volatile fraction of wheat bread, only a relative small number are responsible for the different notes in the aroma profiles of the crust and the crumb. These compounds can be considered as character impact compounds. Approaches to find out the relevant aroma compounds in bread flavors using model systems and the odor unit concept are emphasized in this review. A new technique denominated "aroma extract dilution analysis" was developed based on the odor unit concept and GC-effluent sniffing. It allows the assessment of the relative importance of the aroma compounds of an extract. The application of this technique to extracts of the crust of both wheat and rye breads and to the crumb of wheat bread is discussed. 

We have applied a modified odor unit equation for evaluating aroma quality of the volatiles of Citrus sinensis OSBECK, ev. Shiroyanagi. Although the concept of odor units in flavor research was proposed by Rothe et al. (9) as a objective index of aroma quality, the concentration of individual components in a food (Fc in equation [1]) depends on the extraction efficiency of the essential oils. If the test sample is a solid, we can not calculate the exact concentration. Because the aroma oils, for example, may exist in different cells in the peels of citrus, we cannot take out only specified cells. It does not give a homogeneous concentration. Therefore, the odor units of individual aroma components in a food do not always give a constant value. Equation [1] should be applied to beverages such as apple juice, citrus juice, coffee, milk and so forth. The modified odor unit equation (75) for liquid and solid samples is shown as follows ... 

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