Food flavor components involved

The perception of flavor is a fine balance between the sensory input of both desirable and undesirable flavors. It involves a complex series of biochemical and physiological reactions that occur at the cellular and subcellular level (see Chapters 1-3). Final sensory perception or response to the food is regulated by the action and interaction of flavor compounds and their products on two neur networks, the olfactory and gustatory systems or the smell and taste systems, respectively (Figure 1). The major food flavor components involved in the initiation and transduction of the flavor response are the food s lipids, carbohydrates, and proteins, as well as their reaction products. Since proteins and peptides of meat constitute the major chemical components of muscle foods, they will be the major focus of discussion in this chapter. 

Sulfur compounds are renowned for unpleasant odors beginning with the rotten egg smell of H2S and many are responsible for the off-flavors of various foods. Nevertheless, some sulfur compounds provide the pleasant odors associated with many plants and are also prominent in desirable food flavors. The determination of flavor or aroma is very complex since large numbers of components may be involved both for microorganisms and plants. Many flavor compounds, of course, do not contain sulfur. Much has been and continues to be written. We can only convey an eclectic flavor of the many situations involving sulfur compounds - a tasting menu. The colorful language of experts in aroma and taste bears a close resemblance to that of enophiles. 

The flavor quality of food is a primary factor involved in a consumer s decision to purchase a food item. Therefore, food technologists require a thorough understanding of how flavor deteriorates if they are to prepare products that consumers will purchase repeatedly. This knowledge is particularly important in meat and meat products, since the deterioration of meat flavor is a serious and continual process (1-4) that involves both the loss of desirable flavor components 4,5) and the formation of off-flavor compounds (6-9) many of which are associated with lipid oxidation (10). 

Flavor is the complex effect of three components taste, odor, and feeling factors. It is usually associated with the pleasure of savoring food or beverages and has, subsequently, suffered from considerable imprecision in definition. Flavor is a sensation with multidimensional components involving subjective and objective perceptions. The sensory perceptions are both qualitative as well as quantitative and, therefore, can be measured. Webster s New Collegiate Dictionary defines flavor as the ... quality of something that affects the sense of taste,. .. the blend of taste and smell sensations evoked by a substance in the mouth. This definition is correct, but incomplete, and should be redefined to include feeling factors. 

A second distinguishing factor of thermal oxidations is their more random nature than typical room temperature oxidations. Very high temperatures make more sites available on the fatty acid for oxidation to occur. Thus a wider range in end products (volatile flavor components) will occur. So even though the same chemical mechanisms are involved in flavor formation in deep fat fried foods, the flavor developed is unique to this process. 

An important role is played by adenosine triphosphate (ATP), involved in energy exchange relatively large amounts of free energy are released when ATP is hydrolyzed. A consequence of the loss of ATP in muscle postmortem is its conversion to hypoxanthine. Some 5 -mononucleotides, intermediates in the production of hypoxanthine and with the ribose component hy-droxylated at position 6, are flavor enhancers in muscle foods. Compounds of this kind are, for example, inosine 5 -monophosphate (IMP) and guanosine 5 -monophosphate (GMP). The ATP is first converted to ADP and then to AMP by a disproportionation reaction. The AMP is then de-aminated to IMP. The IMP can degrade to inosine and eventually to hypoxanthine. Hypoxanthine... 

As flavor production in natural food is governed by too complicated reactions due to its complex components (Table II), chemists concentrated their research efforts on simpler systems to understand the reactions involved and their products. 

Osmotic distillation is a relatively new membrane separation process, which is used primarily for the dewatering of liquid food products. The majority of reported applications have involved the production of fruit juice concentrates. The main advantage of OD over vacuum distillation, which is the conventional method for concentrate production, is the preservation of product integrity. Osmotic distillation is operated at mild temperatures (typically ambient), and thereby produces concentrates that are free from the effects of thermal degradation. Also, the delicate volatile flavor and fragrance components that are essential to consumer acceptance of fruit juice concentrates are largely retained. 

Fat A nutrient that is a major source of energy and plays a key role in the absorption of the fat-soluble vitamins A, D. E. and K. Fat components are the primary building blocks of cell membranes and are precursors to hormone-like compounds involved in a number of important physiological processes. Fats also provide foods with flavor and texture. 

Due to its high sensitivity and selectivity, liquid chromatography-mass spectrometry (LC-MS) is a powerful technique. It is used for various applications, often involving the detection and identification of chemicals in a complex mixture. Ultra Performance Liquid Chromatography Mass Spectrometry Evaluation and Applications in Food Analysis presents a unique collection of up-to-date UPLC-MS/MS methods for the separation and quantitative determination of components, contaminants, vitamins, and aroma and flavor compounds in a wide variety of foods and food products. 

In this text, we will spend substantially more time on the aroma of foods than taste or chemesthetic responses. This is largely due to historical reasons. In the past, the flavor industry and those acndenucrans traditionally considered to be flavor chemists have focused their efforts on the aroma sensation. The flavor industry has traditionally sold the food industry nuxtures of volatile constituents that characterize this ccmponent of flavor. In some instancies, elanents of bitterness and occasionally umami (savory flavorings) have also been supplied by the flavor industry. The food industry has added the other components of flavor, e.g., sweeteners, acidulants, and salts. Thus, discussions of the flavor industry have largely ignored much of taste. Only recently has the flavor industry become involved in selling more complete flavor profiles due to opportunities in the marketplace. 

Our interest in the analysis of nonvolatiles, thus, may involve taste substances or substances that indirectly influence taste or aroma. As mentioned earlier, in the first case, we are interested in the analysis of substances that impart sweetness, tartness, bitterness, saltiness, or unmami sensations. The analysis of these substances is reasonably well defined. In the latter case, the analyses employed are less well defined and are unique to the components one wishes to analyze. For example, we may wish to measure substances (e.g., melanoidins) that interact with sulfur aroma compounds (in coffee). There are no standardized methods for the analysis of melanoidins in foods and thus, the protocols have to be developed. In this chapter, we will only briefly discuss the established methods for the analysis of taste substances. Due to the specificity of methods for the analysis of nonvolatiles that may indirectly influence flavor perception, we will only refer the reader to the literature [93-100]. 

Analytical methods for the isolation, separation, and characterization of anthocyanins have been described (Markham, 1982 Jackman et al., 1987 Harbome, 1998 Rivas-Gonzalo, 2003 Andersen and Francis, 2004). A comprehensive and highly recommended source for anyone involved in anthocyanin analysis is that of Strack and Wray (1989). Further details of flavonoid chemistry can be found in volumes of The Flavonoids series (Harbome et al., 1975 Harbome and Mabry, 1982 Harbome, 1988, 1994). Recent advances in flavonoid research are thoroughly described in the book Flavonoids Chemistry, Biochemistry and Applications, edited by Andersen and Markham (2006). Extensive information on the occurrence of anthocyanins in various natural products reported after 1992 was presented by Andersen and Jordheim (2006). One of the most useful sources of current protocols of anthocyanin analysis is the Handbook of Food Analytical Chemistry, Pigments, Colorants, Flavors, Texture, and Bioactive Food Components, edited by Wrolstad et al. (2004). This book is a practical how to manual that contains detailed in-stmctions on the following topics (1) extraction, isolation, and purification of anthocyanins, (2) characterization and measurement of anthocyanins by UV-Vis... 

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