Contribution to food flavor

Considerable effort has been made to examine the volatiles and trace components that contribute to food flavors. Sone early techniques for measuring the volatile components in food products by gas chromatography consisted of analyzing headspace vapors to detect vegetable and fruit aromas (5) and volatiles associated with other food materials ( ). AlTo, sample enrichment has been used in the analysis of Tome food products. However, these techniques require steam distillation or extraction and concentration, or both, before the volatile mixture can be introduced into a gas chromatograph (, 9, 10). Besides being... 

G. P. Rizzi, The Strecker degradation and its contribution to food flavor, in Flavor Chemistry Thirty Years of Progress, R. Teranishi, E. L. Wick, and I. Homstein (eds), Kluwer/Plenum, New York, 1999, 335-343. 

Each compound has a characteristic note and a specific threshold which makes its contribution to food flavor unique. But none of the individual compounds were reported to completely produce the characteristic flavor of the processed food. This indicates that the food flavors are of mixed flavor notes of numerous compounds, while others are necessary for its synergistic effect, others exert a background of modifying effect. 

Lipids may contribute to food flavor formation through participation in other chemical pathways, most notably, the Maillard reaction. Whitfield [42] has provided a very comprehensive review of how lipids and their degradation products may participate in the Maillard reaction. He lists the primary means of interaction as ... 

The central question that I want to approach here is the possible relationship between flavor preferences and nutritional value. There are a lot of data to work with. More than 70(X) volatile flavor substances have been identilied in foods and beverages. The situation may not be quite as complex as this would suggest. While it is true that any single fruit or vegetable may synthesize a few hundred volatile compounds, only a modest subset of these will contribute to its flavor profile. So the task is to sort out what these are, identify their sources, and link, where possible, these sources to nutritional value. Studies with the tomato provide a great example. The bottom line is Virtually all of the major tomato volatiles can be linked to compounds providing health benefits to humans. ... 

Individuals may experience a broad array of flavor sensations within one meal or even one food. The interactions among the sensations makes it difficult to separate and quantify individual contributions to tiie flavor experience. An individual stimulus may elicit more than one sensation, and be processed at the recognition and transduction steps by more than one mechanism. In addition, individual differences in sensory responses may provide different assessments of the same event. 

A mouth simulator is a valuable tool when determining what volatiles contribute to the flavor sensation during consumption of a food. This includes determining potency (e.g., Char-mAnalysis), intensity (e.g., OSME Acree and Barnard, 1994), contribution (e.g., omission tests), and effect of a compound on the flavor. Sample preparation with a mouth simulator gives a close representation of the human experience, without the expense and variability of using humans. The limitations of headspace sampling and detection sensitivity define the limits of the use of mouth simulators. 

It should be kept in mind that most analytical instruments, such as gas chromatographs and mass spectrometers, do not discriminate between volatile compounds that do or do not possess odor activity. Some form of sensory analysis must be conducted in order to select which volatile compounds contribute to the flavor of the foods. Gas chromatography-olfactometry (GC/O) is an important tool to accomplish that task. 

Furthermore, as an extract of a natural product is concentrated, the number of odorants detected increases indefinitely. Clearly, most of the odorants in a natural product are below their odor threshold, and it is only the most potent compounds that are involved in generating the flavor response. An odorant can be very potent at extremely low concentrations if it has an extremely low odor threshold, (unit go). In practice, early GC/O analysts attempted to concentrate the sample as far as possible to identify as many potential odorants as possible. Compositional studies combined with threshold studies were then used to sort out the important odorants from the ones that did not contribute to the flavor experience. Rothe s odor units (OU = concentration in sample/threshold in sample) were an early attempt to rank odorants by potency. The process of determining OU values for a food required a lot of chemical and psychophysical analysis. Dilution analysis was developed to produce an OU-like value directly from GC/O without the need to know the identity of the odorant. In fact, the real value of dilution analysis is that it can tell the analyst which compounds to identify. 

In the following chapter, methods enabling the selection of those odorants contributing mainly to food flavors will be discussed with special emphasis on sensory experiments aimed to verify the flavor potency of the proposed key odorants. Furthermore, strategies to characterize flavor precursors in the raw materials will be described. 

The data indicate that if the respective precursor is present and if the processing conditions are similar, the same odorant will contribute to the flavors of different foods. However, HDF has been detected also as a potent odorant in unprocessed foods like strawberries [48], pineapple [91] and, very recently, in Emmentaler cheese [30] indicating alternative biochemical pathways in HDF formation. 

Comparison of the taste threshold with estimated concentration in orange juice (where available) in Table I reveals that in all cases except octyl acetate and a-pinene, the concentration in orange juice exceeds the taste threshold in water for most values reported. Patton and Josephson (17) postulated that components present in a food at above threshold level make a positive contribution to the flavor, while those present at below threshold level make little or no contribution to flavor. This generalization is now considered an oversimplification, for synergistic effects among food constituents have been shown to decrease the threshold level of some compounds, and nonvolatile constituents are known to either increase or decrease the taste threshold of certain volatile and nonvolatile constituents. 

Some pyrrole derivatives have pleasant flavor. For example, pyrrole-2-carboxaldehyde gives a sweet and corn-like odor and 2-acetylpyrrole has caramel-like flavor. However, some pyrroles have been found to contribute to off-flavor of food products (24). Pyrroles have not received as much attention as flavor components as other heterocyclic Maillard reaction products such as pyrazines and thiazoles even though the number of derivatives identified is almost the same as that of pyrazines (Figure 1). Proposed formation mechanisms of pyrroles in the Maillard reaction systems are similar to those of thiophenes (Figures 2). 

A more general approach to estimate the importance of a flavor compound in a particular food is the calculation of the ratio of its concentration to its flavor (odor and taste) threshold (9) or to its odor threshold (1 , 11) The result is denoted "aroma value" 19), "odor unit" (10) or "odor value" (11) the higher the value or unit, the more intensely this component contributes to the flavor or odor of the food. 

By applying the concept of odour values (2j[) to this class of compounds only Furaneol and Maltol contribute to coffee flavor. Both constituents are known as important flavor compounds and are used as nature identical flavorings in many foods. Furaneol contributes a fragrant caramel note to coffee and is known as important compound in pinapple and strawberries. The consumption of Furaneol in the USA in these products is respectively 41,800 to 2,650 to 1,100 kg (per year) compared to 2,718 kg of synthesized Furaneol used in nature identical flavoring. Similar figures were presented for Maltol and other coffee compounds by Stofberg and Grundshober (8J. 

Ketones Aliphatic ketones formed by autoxidation of lipids also contribute to the flavor of oils and food products. For example, Guth and Grosch (13) identified l-octen-3-one as one of the odor-active compounds in reverted soybean oil. This compound was described as metallic and mushroom-like. The reaction pathway for the formation of l-octen-3-one from the linoleate-10-hydroperoxide via the p-scission route is illustrated in Figure 2. 10-Hydroperoxide of linoleate is not the usual hydroperoxide formed by autoxidation of linoleate however, it is one of the major hydroperoxides formed by the photosensitized oxidation (singlet oxygen reaction) of linoleate (14). 

Van den Ouweland, G. A.M. Components contributing to beef flavor. Volatile compounds produced by the reaction of 4-hydroxy-5-methyl-3(2//)-fiiranone and its thio analog with hydrogen sulfide. J. Agric. Food Chem. 1975, 23, 501-505. 

Tobacco, unlike most other commodities, is not produced as a food crop, but it is used for manufacture of smoking materials and other products. The essential oils in tobacco are important for impact and balance in smoking (11). Smoking pleasure is derived from a balance of nicotine and volatile components. Tobacco chemists and flavorists are certain that carotenoid derivatives contribute to smoke flavor and aroma (5) Over a hundred compounds related to carotenoids have been isolated from tobacco and tobacco smoke. 

Xylenols which are clear crystalline compounds soluble in alcohol, acetone, and many organic solvents, are present in various essential oils and also in tea, tobacco, roasted coffee, and in various smoked foods. In some cases xylenols contribute to the flavor of these products [1]. 

Before reporting the contributions of sweeteners to food flavor, the results of certain studies undertaken to add fundamental flavor information about the various natural sweeteners, such as their likenesses and differences, the variations in their detectability at different levels, and their action with the other basic taste factors are presented. 

Piperidine and -piperidine were first identified by Neurath et al. in 1965 (2749) and 1966 (2734), respectively [see Table 3 in Neurath (2724)]. The piperidines in tobacco and tobacco smoke are found as substituted ketones, acids, and alkyl derivatives. None of the forty-eight nonaromatic six-membered A-heterocycles found in tobacco and tobacco smoke has been shown to provide positive contributions to the flavor of tobacco smoke, although piperidine is on the GRAS list as a food flavor (3215). 

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