Flavor, analysis using atmospheric

Another powerful technique known as aroma extract dilution analysis is used to determine the most significant odor and flavor compounds in a complex mixture in a food product. This method determines the odor activity of volatile compounds in an extract eluted from a high-resolution capillary GC-SP column (see Table 11.9). The odor activity or impact of a compound is expressed as the flavor dilution factor (FD), which is the ratio of its concentration in the initial extract to its concentration in the most dilute extract in which the odor can be detected by GC-SP. However, the information from this technique may be of limited practical value, because it ignores the significant effect of food matrices on flavor and odor perception of mixtures of flavor and odor compounds. Advanced instrumental techniques have been developed for flavor analysis during food consumption. These techniques permitting direct mass spectrometry at atmospheric pressure are discussed in Chapter 6. 

Munson and Field reported in 1966 on a technique of ionizing molecules by gas phase ion-molecule reactions, which they called chemical ionization (Cl). In this way, break-up of the molecules can be greatly reduced or even avoided. Thus, measured ion currents can be correlated with the densities of the respective parent neutral compounds, allowing for on-line monitoring of rather complex gas mixtures. The fundamental principles of gas phase ion chemistry on which Cl is based, as well as the instrumentation for Cl, have been reviewed in great detail by Harrison." The wide variety of Cl methods that has been developed includes Medium Pressure Mass Spectrometry, Fourier Transform Mass Spectrometry, Quadrupole Ion Trap Mass Spectrometry, Pulsed Positive Ion-Negative Ion Chemical Ionization, and Atmospheric Pressure Ionization Mass Spectrometry (API-MS). Of these, API-MS has developed into a very reliable and widely used technique for analysis of VOCs in flavor release studies and human breath. A variety of API-MS applications in these fields of research has been described in a recent volume by Roberts and Taylor. ... 

Modified Atmosphere Stored Broccoli Florets. Since TBHQ and caraway seed flavonoid components exhibited the same effect on depletion of methanethiol in model systems, they were examined for efficacy in suppressing methanethiol-related off-flavors in broccoli florets stored under modified atmospheres. Freshly prepared broccoli florets (ca 3 cm long) were treated by dipping them in cell-free cni caraway seed extracts or aqueous TBHQ solutions (100 ppm), and allowing excess liquids to drain off. Control samples were dipped in distilled water. Broccoli samples were placed in the heat-sealed Curlon 850 pouches described earlier (70 g/pouch), and then held under refrigeration at 4°C until used for GC-FPD and descriptive sensory analysis 8 days later. 

After the extraction, lipids may be subjected to further treatment, like filtering or centrifugation, and are usually dried to remove any residual moisture, which may alter the analysis that follows. Since unsaturated lipids are prone to auto-oxidation and formation of off-flavors and harmful products can occiu within any of these analytical steps, a number of precautions are usually taken, to keep oxidation to a minimum. These consist of the addition of antioxidant agents, the use of a nitrogen atmosphere, as well as control of the exposure to light and temperature. 

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