Flavor instrumental techniques

Flavor Volatiles as Measured by Rapid Instrumental Techniques... 

Ranid instrumental techniques were used to elucidate off-flavor problems in raw and processed rice products, raw and roasted peanuts, and corn-soy food blends. Less than a gram of the solid material was secured in a standard or special injection port liner of the gas chromatograph. Then, the volatiles from the sample were steam distilled in situ and identified by combined gas chromatography/mass spectrometry. 

Lee, W.E. 111. 1986. A suggested instrumental technique for studying dynamic flavor release from food products. 7. Food Sci. 51 249-250. 

The authors of this book provide an update of the methodology used in flavor research. Many improvements in instrumental sensitivities and capabilities have accrued in recent years, and state-of-the-art instrumentation and instrumental techniques for flavor analyses compose a substantial portion of this volume. New methods for extracting, derivatizing, and otherwise manipulating flavor compounds are another important part of this book, as are the chapters that deal with sensory evaluation. As editors, we are grateful to the authors for their contributions and to our respective employers for their support of our effort. 

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. 

H. Advanced instrumental techniques for volatile flavor analysis... 

Legendre, M.G., H.P. Dupuy, Flavor volatiles as measured by rapid instrumental techniques, in Protein Funct. Foods, Amer. Chem. Soc., Washington, D.C., 1981, p. 41. 

It has been a long term goal of many researchers to use instrumental means to replace some sensory functions. The use of sensory panels for quality control purposes presents many problems which may be minimized through the use of supplementary instrumental techniques. Over the years, gas chromatography and mass spectrometry have found limited application for this purpose. Recently an instrument generically called an "electronic nose" has been commercialized. This paper will present a brief overview of gas chromatographic and mass spectral techniques used to monitor flavor quality in foods but focus on the new electronic nose instruments. 

The book can be categorized into three parts sample preparation and instrumentation techniques, application examples, and olfactometry. The final two chapters discuss MS-based electronic nose applications (Chapter 13) and the chemical structures of flavor and off-flavor chemicals in various types of foods (Chapter 14). 

An integrated GC/IR/MS instrument is a powerful tool for rapid identification of thermally generated aroma compounds. Fourier transform infrared spectroscopy (GC/IR) provides a complementary technique to mass spectrometry (MS) for the characterization of volatile flavor components in complex mixtures. Recent improvements in GC/IR instruments have made it possible to construct an integrated GC/IR/HS system in which the sensitivity of the two spectroscopic detectors is roughly equal. The combined system offers direct correlation of IR and MS chromatograms, functional group analysis, substantial time savings, and the potential for an expert systems approach to identification of flavor components. Performance of the technique is illustrated with applications to the analysis of volatile flavor components in charbroiled chicken. 

This procedure applies both to the assay of flavor chemicals and to the quantitation of minor components in flavor chemicals. Analysts following this procedure and performing the test should obtain sufficient resolution of major and even trace components of a mixture to calculate accurately the concentration of the desired component should be familiar with the general principles, usual techniques, and instrumental variables normally met in gas chromatographic analysis and should pay particular attention to the following ... 

The flavor impression of a food is influenced by compounds that affect both taste and odor. The analysis and identification of many volatile flavor compounds in a large variety of food products have been assisted by the development of powerful analytical techniques. Gas-liquid chromatography was widely used in the early 1950s when commercial instruments became available. Introduction of the flame ionization detector increased sensitivity by a factor of 100 and, together with mass spectrometers, gave a method for rapid identification of many components in complex mixtures. These methods have been described by Teranishi et al. (1971). As a result, a great deal of information on volatile flavor components has been obtained in recent years for a variety of food products. The combination of gas chromatography and mass spectrometry can provide identification and quantitation of flavor compounds. However, when the flavor consists of many compounds, sometimes several hun-... 

Background. As an analytical technique, tandem mass spectrometry is just entering its second decade of development. The variety of reported applications belies its relative youth. Tandem mass spectrometry (MS/MS) grew out of early work which used metastable ion transitions in order to establish ion structures and interrelationships. After extensive applications to ion structural studies, its usefulness in direct catplex mixture analysis became apparent with the early work of Cooks (1-3). Its successes in problem solving are summarized in a recent book edited by McLafferty (4). New, with several ccnmercial instruments available, MS/MS is being evaluated for application in several new areas, including biochemical analysis, forensic chemistry, and food and flavor analyses. The principles of MS/MS will be surmarized in the first part of this chapter. The second part of the chapter will deal with the reported applications of MS/MS to flavor analysis. 

As a result of the availability of sophisticated Instrumentation and separation techniques some remarkable progress has already been made In meat flavor research and this trend Is expected to continue. Although a variety of factors are known to affect the development of meat flavor, no single compound/group of compounds, or factor has yet been found that could play the principle role and the true chemical nature of meat flavor, and particularly species differentiation. Is not fully understood. Most Importantly very little Is known about the origin of cured-meat flavor. The curing process seems to simplify the composition of the volatile constituents and eliminates the overtones related to species-specific flavor notes. Thus, work in this area would have a major impact in meat-flavor research and may prove to be extremely... 

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. ... 

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. 

In headspace SPME, there are two processes involved the release of analytes from their matrix and the adsorption of analytes by the liber coating. The volatile organic analytes are extracted, concentrated in the coating and transferred to the analytical instrument for desorption and analysis. In comparison to well-established techniques, SPME is inexpensive, solvent free, and convenient. In addition, because relatively mild conditions can be used, i.e., systems at equilibrium and temperatures less than 50°C, SPME gives a better quantitative estimate of the flavor profile. ... 

Descriptive profiling techniques provide for the intelligent use of human subjects as measuring instrument. When properly trained, human subjects can be effective analytical instruments able to accurately analyze flavor and aroma attributes present in a food system, and to generate statistical comparisons of samples products. 

The contribution of sulfur compounds to the flavor and off-flavor characteristics of foods has been studied for many years. Advances in analytical techniques and instrumentation and mechanistic studies have led to a better understanding of the formation and mode of action of these compounds. Recent interest, however, has focused on their importance in areas other than flavor. The role of dietary sulfur compounds as anticarcinogens, antimicrobials, and antioxidants has been and continues to be extensively studied. 

In addition, the potential of combined gas chromatography-mass spectrometry (GC-MS) for determining volatile compounds, contained in very complex flavor and fragrance samples, is well known. The subsequent introduction of powerful data acquisition and processing systems, including automated library search techniques, ensured that the information content of the large quantities of data generated by GC-MS instruments was fully exploited. The most frequent and simple identification method in GC-MS consists of the comparison of the acquired unknown mass spectra with those contained in a reference MS library. 

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