Flavor analysis method

A general discussion of flavor analysis, including both historical material and specific applications, in which GC/O is described in the context of the most common methods of flavor analysis. 

Epoxy is used as a lining for water reservoirs, water mains, and home plumbing systems (Heim and Dietrich, 2007a). These applications can impact sensory quality of tap water in food manufacturing, food service operations, and residential homes. This effect may be most noticeable in water but residual aroma and flavor compounds may cause a taint in foods prepared with these water sources. An odor assessment, using a water industry standard flavor profile analysis method, identified a strong relationship between water (simulated tap water, pH 7.7-7.9) stored in epoxy-lined copper pipes for 3-4 days and an odor described... 

The precursor analysis approach should now be seen as a useful complement to traditional methods of flavor analysis of fruits. The latter methods are often limited to the painstaking processes of isolation and identification of those trace constituents which are directly responsible for flavor. The precursor analysis approach takes advantage of the evidence provided by Nature vhen secondary metabolites, including flavor corpounds, are biochanically transformed and accumulated by the fruit. 

Solid-phase microextraction (SPME) is a technique that was first reported by Louch et al. in 1991 (35). This is a sample preparation technique that has been applied to trace analysis methods such as the analysis of flavor components, residual solvents, pesticides, leaching packaging components, or any other volatile organic compounds. It is limited to gas chromatography methods because the sample must be desorbed by thermal means. A fused silica fiber that was previously coated with a liquid polymer film is exposed to an aqueous sample. After adsorption of the analyte onto the coated fiber is allowed to come to equilibrium, the fiber is withdrawn from the sample and placed directly into the heated injection port of a gas chromatograph. The heat causes desorption of the analyte and other components from the fiber and the mixture is quantitatively or qualitatively analyzed by GC. This preparation technique allows for selective and solventless GC injections. Selectivity and time to equilibration can be altered by changing the characteristics of the film coat. 

As seen from Figures 4, 5 and 6 each sample preparation method yielded a different flavor analysis. However, when combined, the results revealed a very complex and more complete profile of dried Shiitake mushrooms flavor. 

Methods used in the chemistry of natural substances, particularly in the coffee field, were reviewed by Reymond (1974), and the techniques for flavor analysis by Merritt and Robertson (1982) and by Adda and Jounela-Eriksson (1979). 

AOCS has a recommended practice (Cg 3-91) for assessing oil quality and stability (AOCS, 2005) for measuring primary and secondary oxidation products either directly or indirectly. For example, peroxide value analysis (AOCS method Cd 8-53) (AOCS, 2005) determines the hydroperoxide content and is a good analysis of primary oxidation products. To determine secondary oxidation products, the procedure recommends p-anisidine value (AOCS Method Cd 18-90, 2005) volatile comlb by gas chromatography (AOCS Method Cg 4-94, 2005) and flavor evaluation. (AOCS Method Cg 2-83, 2005). The anisidine value method determines the amounts of aldehydes, principally 2-alkenals and 2, 4-dienals, in oils. The volatile compound analysis method measures secondary oxidation products formed during the decomposition of fatty acids. These comlb can be primarily responsible for the flavors in oils. The... 

Headspace Technique. One of the most recent methods of flavor analysis which evolved with the development of sensitive gas chromatographic instrumentation is the headspace technique. Withycombe et al (19), gave an excellent description of headspace analysis. In this procedure volatiles in gaseous state that are in equilibrium over the food are analyzed. 

Because most flavor components are highly volatile, El and Cl GC-MS have been primary techniques in flavor analysis and research since the early 1960s. For example, 1000 discrete compounds have been identified in coffee volatiles using capillary GC-MS methods. 

There are six or seven other descriptive analysis methods described in the sensory literature. The methods include Flavor Profile (CairuCTOSS and Sjdstrom, 1950) or its current version. Spectrum Analysis (Meilgaard et al., 2006), Texture Profile (Brandt et al., 1963), Free Choice Profiling (Williams and Arnold, 1985), and its successor Hash Descriptive Analysis (Dairou and Sieffermann, 2002). There are other methods described in the literature, but all appear to be based on methods previously described. 

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. 

PTR-MS as a New Methodology for Analyzing Flavor Release Recently, thanks to the pioneering work by Dronen and Reineccius (2003), proton transfer reaction mass spectrometry (PTR-MS) has been used as a rapid analysis method to measure the release time-course of flavors from spray-dried powders. The traditional equiUbrium method for flavor release mentioned above is extremely time-intensive, and commonly several weeks are necessary to obtain a full release profile of the flavor from the powder. The PTR-MS method has been applied extensively to analyze the release... 

Guntert, M., G. Krammer, H. Sommer, P Werkhoff, The importance of vacuum headspace methods for the analysis of fruit flavors, in Flavor Analysis, C.J. Mussinan, M.J. Morello, Eds., Amer. Chem. Soc., Washington, D.C., 1998, p. 38. 

The experiments were carried out on two different days using the same batch of popcorn, but freshly popped each time just before the experiment. The direct injection method results should represent the true nature of the sample as extracted by supercritical CO2. The aims of this experiment were to apply the use of the SFE SPME and SFE DI methods in volatile compound analysis for the first time and to evaluate the feasibility of using this technique for flavor analysis from difficult solid matrices using smaller sample quantities. 

Table 1 Design of the Experiments Carried Out to Evaluate Sampling and Analysis Methods for Analysis of the Model Food (Five Flavor Compounds in Sunflower Oil) ...

As we have already emphasized in this chapter, aroma profiles depend on the extraction method used. There is no universal extraction procedure in food flavor analysis, and different methods will influence aroma profiles. The new SAFE technique presented above represents an attractive approach in flavor research and a new tool for isolating and concentrating volatile components from solid or aqueous food materials. For that reason, the SAFE technique is expected to be widely applied in the future for highly efficient extraction of flavor components from various food samples. 

The objective of modern flavor analysis is to qualitatively and quantitatively determine the flavor profile imparted by nature and thus to identify those substances responsible for the flavor of a food. In recent years, a combination of sensory methods and instrumental analytical procedures has made a major contribution toward reaching this objective. Thanks in particular to the concept of odor activity value, which has been steadily refined at the German Research Institute for Food Chemistry in Garching (Technical University of Munich) during the past decade, it is today possible to make well-founded statements about the odor activity of volatile flavor compounds in foods (112-116). With the aid of the odor activity value concept, it is possible to identify those components of the extremely complicated flavor profiles that are of key importance for the specific flavor of a food. 

The method of choice for exact quantitative determination of key flavorrelevant constituents in foods is currently IDA, isotope dilution analysis (stable isotope dilution assay or SIDA), in which the isotope-labeled analog used as the internal standard undergoes the same losses during workup as does the analyte. Either radioactive or stable isotopes can be used for the isotope dilution method. The latter are simpler and can be handled without health risks. For this reason, only stable isotopes are used in flavor analysis. 

Various methods have been developed to eliminate biases which otherwise can skew results. The wines must be presented without identification, although the taster should be told the type of wines (the best strawberry wine should rate very poorly in a Cabernet class). Eor the most informative results, many details of coding, presentation order, repHcation, etc must be considered. The results must be statistically examined to estimate whether or not they could have been obtained accidentally. Statistical analysis is an entire field in and of itself, and wine studies have contributed greatly to its present sophistication, as appHed in the flavor field. 

Flavor Description. TypicaHy, a sensory analyst determines if two samples differ, and attempts to explain their differences so that changes can be made. The Arthur D. Litde flavor profile (FP), quantitative descriptive analysis (QDA), and spectmm method are three of the most popular methods designed to answer these and more compHcated questions (30—33). AH three methods involve the training of people in the nominal scaling of the flavor quaHties present in the food being studied, but they differ in their method for quantitation. 

Exposure to a flavor over time always results in a decrease in the perceived intensity. This dynamic effect of flavorants, called adaptation, is a central part of the process by which people experience flavors in foods as well as in sensory tests. Measuring the dynamics of flavor perception is an emerging technology made possible by inexpensive computing. Called time-intensity analysis, these methods are finding wide appHcations in taste analysis. 

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