Taste flavor perception

The aroma of fmit, the taste of candy, and the texture of bread are examples of flavor perception. In each case, physical and chemical stmctures ia these foods stimulate receptors ia the nose and mouth. Impulses from these receptors are then processed iato perceptions of flavor by the brain. Attention, emotion, memory, cognition, and other brain functions combine with these perceptions to cause behavior, eg, a sense of pleasure, a memory, an idea, a fantasy, a purchase. These are psychological processes and as such have all the complexities of the human mind. Flavor characterization attempts to define what causes flavor and to determine if human response to flavor can be predicted. The ways ia which simple flavor active substances, flavorants, produce perceptions are described both ia terms of the physiology, ie, transduction, and psychophysics, ie, dose-response relationships, of flavor (1,2). Progress has been made ia understanding how perceptions of simple flavorants are processed iato hedonic behavior, ie, degree of liking, or concept formation, eg, crispy or umami (savory) (3,4). However, it is unclear how complex mixtures of flavorants are perceived or what behavior they cause. Flavor characterization involves the chemical measurement of iadividual flavorants and the use of sensory tests to determine their impact on behavior. 

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. 

Food colorants play an important role in quality perception. Color is often the first notable characteristic of a food and it influences the expectations of consumers buying the product and also influences food handlers who make quality-related decisions, for example, during visual inspections." More specifically, color predetermines our expectations and perceptions of flavor and taste. " Color is interrelated with flavor intensity (detection threshold), with sweetness and salinity sensations, and also with our susceptibilities to and preferences for products. For example, consumers perceived a strongly red-colored strawberry-flavored drink to be sweeter than a less colored version, and yellow was associated with lemon and pink with grapefruit, but by reversing the colors, flavor perception changed." If food color is not appealing, consumers will not enjoy the flavor and texture of the food. ... 

Tikk, M. Tikk, K. T0rngren, M. A. Meinert, L. Aaslyng, M. D. Karlsson, A. H. Andersen, H. J. Development of Inosine Monophosphate and Its Degradation Products during Aging of Pork of Different Qualities in Relation to Basic Taste and Retronasal Flavor Perception of the Meat. J. Agric. Food Chem. 2006, 54, 7769-1711. 

Figure 1. Representation of the 2-faces of flavor perception showing desirable and undesirable smell (odor) and taste (gustatory) input components.

Role of Odor in Flavor Perception. In terms of total flavor sensalion. many authorities agree that odor is usually more important lhan taste. Experience, of course, demonstrates the marked reduction of flavor sensation when the nasal passages are partially blocked, as in the case of a common cold. In such instances, the layperson may refer to the "flat taste" of the food. In actuality, the taste buds are functioning normally it is the odor componeni of flavor that is missing. 

Double emulsions are also very useful for food application. Sensitive food materials and flavors can be encapsulated in w/o/w emulsions. Sensory tests have indicated that there is a significant taste difference between w/o/w emulsions and o/w emulsions containing the same ingredients, and that there is a delayed release of flavor in double emulsions [61]. W/o/w or o/w/o multiple emulsions having a concentrated aqueous-soluble flavor or a concentrated oil-soluble flavor encapsulated in the internal phase can be prepared. Food products obtained with these particulates exhibit enhanced flavor perception and extended shelf-life [62]. 

Flavor plays a critical role in determining the quality of a food emulsion during consumption. The term flavor refers to those volatile components in foods that are sensed by receptors in the nose (aroma) and those nonvolatile components that are sensed by receptors in the tongue and the inside of the mouth (taste) (122, 123). In addition, certain components in foods may also contribute to flavor because of their influence on the perceived texture (mouthfeel) (124). The flavor of a food is therefore a combination of aroma, taste, and mouthfeel, with aroma usually being the most important (122). Flavor perception is an extremely complicated process that depends on a combination of physicochemical, biological, and psychological phenomena (125). Before a food is placed in the mouth, its flavor is perceived principally through those volatile components that are inhaled directly into the nasal cavity. After the food is placed in the mouth, the flavor is determined by nonvolatile... 

The human sensory apparatus varies in sensitivity from person to person. Therefore, in the selection of panelists for sensory evaluation purposes the first step is to establish the limits of their sensory capacities by determining their perception thresholds for basic tastes, flavor, and odor recognition. 

Food flavor is the sensory impression of a food and is determined mainly by the chemical senses of taste and smeU given by the food. The senses, which detect chemical irritants in the mouth as well as temperature and texture, are very important to the flavor perception. The existing flavor of the food can be enhanced with natural or artificial flavorants, which affect these senses, i.e., making the food products taste more savory, so-called avor enhancers. The primary function of the flavor in food is the flavoring rather than nutritional. Flavorant is the chemical substance or exfiact that gives or enhances the flavors of natural food product or creates flavor... 

Flavor is a combination of taste, sensation, and odor transmitted by receptors in the mouth (taste buds) and nose (olfactory receptors). The stereochemical theory of odor is discussed in the essay that precedes Experiment 16. The four basic tastes (sweet, sour, salty, and bitter) are perceived in specific areas of the tongue. The sides of the tongue perceive sour and salty tastes, the tip is most sensitive to sweet tastes, and the back of the tongue detects bitter tastes. The perception of flavor, however, is not so simple. If it were, it would require only the formulation of various combinations of four basic substances—a bitter substance (a base), a sour substance (an acid), a salty substance (sodium chloride), and a sweet substance (sugar)—to duplicate any flavor In fact, we cannot duplicate flavors in this way. The human possesses 9,000 taste buds. The combined response of these taste buds is what allows perception of a particular flavor. 

The very broad nature of flavor perception cannot be addressed in a single chapter and thus the book edited by Taylor and Roberts [3] is recommended for a better appreciation of the overall phenomenon of flavor perception. Limitations in terms of space (and of the author) result in this text focusing discussion on the traditional aspects of flavor, i.e., olfaction, taste, and the somatosenses. These fundamental sensory inputs will be discussed in terms of their functioning in the human to help the reader gain an appreciation of the complexity of flavor perception. 

Rawson, N.E., X. Li, The cellular basis of flavour perception taste and aroma, in Flavor Perception, A.J. Taylor, D.D. Roberts, Eds., Blackwell Publ., Ames, 2004, p. 57. 

With this said, the following discussion will be weighted towards the analysis of volatile substances for two reasons. The first is that aroma is unquestionably important to flavor perception. The second is that there is less work published on the analysis of taste (nonvolatile substances). We have a poor understanding how taste/texture stimuli support flavor perception and limited methodology or data to discuss. 

Taste has generally been thought of as a relatively simple sense being composed of salt, sweet, sour, bitter, and umami sensations (Chapter 1). This simplification is not justified since it is clear that each basic taste sensation has many nuances. Furthermore, it is worthwhile to note that each taste sensation supports a different overall flavor perception. For example, if one uses citric acid in a food system, the citrus notes of the flavor will be enhanced. Phosphoric acid is intimately associated with certain cola flavors. Tartaric acid supports grape flavors. Thus, while each acidulant gives a unique sensory character (taste), it also influences our overall flavor perception (interaction to give an overall flavor perception). 

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]. 

Hollowood, T.A., J.M. Davidson, L. DeGroot, R.S.T. Linforth, A.J. Taylor, Taste release and its effect on overall flavor perception, in Chemistry of Taste Mechanisms, Behavior, and Mimics, P.G.D. Paredes, Ed., Amer. Chem. Soc., Washington, D.C.,... 

Food flavor, taste, and texture sensations are perceived over time during consumption, and intensity of flavor perception can change over time. The temperature of the product, after time, equilibrates with the mouth temperature. Physical manipulations such as tongue movements, mastication, and salivary dilution affect the product and its sensory characteristics over time. The classic methods of descriptive sensory analysis do not take into account this temporal dimension. For that purpose, dynamic methods such as time-intensity analysis were developed [13]. 

For a terrestrial animal, flavor may be defined as the composite sensation resulting from placing something in the mouth. Therefore, flavor may Include taste, olfactory, vomeronasal, trigeminal and other chemical sense Inputs as well as tactile, temperature and proprioceptive cues. Thus, the subjective sensation we call flavor is the result of interactions of a complex of receptors. The bulk of experimental work in this field has focussed upon one class of receptors and associated CNS processes, the taste system. There are powerful arguments that the taste system is a uniquely important component in regulating flavor perception and food Intake (e.g.,, but other sensory components significantly influence flavor perception (e.g., ). 

Human perception creates difficulty ia the characterization of flavor people often, if not always, perceive flavors differently due to both psychological and physiological factors. For example, certain aryl thiocarbamates, eg, phenylthiocarbamide, taste exceedingly bitter to some people and are almost tasteless to others (5). This difference is genetically determined, and the frequency of its occurrence differs from one population to another 40% of U.S. Caucasians are nontasters, whereas only 3% of the Korean population caimot perceive the strong bitter taste of the aryl thiocarbamates (6). Similar differences were found ia the sense of smell for compounds such as menthol, carvone, and ethyl butyrate (7). 

Sensory perception is both quaUtative and quantitative. The taste of sucrose and the smell of linalool are two different kinds of sensory perceptions and each of these sensations can have different intensities. Sweet, bitter, salty, fmity, floral, etc, are different flavor quaUties produced by different chemical compounds the intensity of a particular sensory quaUty is deterrnined by the amount of the stimulus present. The saltiness of a sodium chloride solution becomes more intense if more of the salt is added, but its quaUty does not change. However, if hydrochloric acid is substituted for sodium chloride, the flavor quahty is sour not salty. For this reason, quaUty is substitutive, and quantity, intensity, or magnitude is additive (13). The sensory properties of food are generally compHcated, consisting of many different flavor quaUties at different intensities. The first task of sensory analysis is to identify the component quahties and then to determine their various intensities. 

Flavor Intensity. In most sensory tests, a person is asked to associate a name or a number with his perceptions of a substance he sniffed or tasted. The set from which these names or numbers are chosen is called a scale. The four general types of scales are nominal, ordinal, interval, and ratio (17). Each has different properties and allowable statistics (4,14). The measurement of flavor intensity, unlike the evaluation of quaUty, requires an ordered scale, the simplest of which is an ordinal scale. 

A persistent idea is that there is a very small number of flavor quaUties or characteristics, called primaries, each detected by a different kind of receptor site in the sensory organ. It is thought that each of these primary sites can be excited independently but that some chemicals can react with more than one site producing the perception of several flavor quaUties simultaneously (12). Sweet, sour, salty, bitter, and umami quaUties are generally accepted as five of the primaries for taste sucrose, hydrochloric acid, sodium chloride, quinine, and glutamate, respectively, are compounds that have these primary tastes. Sucrose is only sweet, quinine is only bitter, etc saccharin, however, is slightly bitter as well as sweet and its Stevens law exponent is 0.8, between that for purely sweet (1.5) and purely bitter (0.6) compounds (34). There is evidence that all compounds with the same primary taste characteristic have the same psychophysical exponent even though they may have different threshold values (24). The flavor of a complex food can be described as a combination of a smaller number of flavor primaries, each with an associated intensity. A flavor may be described as a vector in which the primaries make up the coordinates of the flavor space. 

Whatever the physiology of odor perception may be, the sense of smell is keener than that of taste (22). If flavors are classed into odors and tastes as is common practice in science, it can be calculated that there are probably more than 10 possible sensations of odor and only a few, perhaps five, sensations of taste (13,21,35—37). Just as a hereditary or genetic factor may cause taste variations between individuals toward phenylthiourea, a similar factor may be in operation with odor. The odor of the steroid androsterone, found in many foods and human sweat, may eflcit different responses from different individuals. Some are very sensitive to it and find it unpleasant. To others, who are less sensitive to it, it has a musk or sandalwood-like smell. Approximately 50% of the adults tested cannot detect any odor even at extremely high concentrations. It is befleved that this abiUty is genetically determined (38). 

Taste and Flavor. The taste effect is generally sweet, but depends strongly on the base of preparation. Eor tasting purposes, vanillin is often evaluated in ice-cold milk with about 12% sugar. A concentration of 50 ppm in this medium is clearly perceptible. Vanilla is undoubtedly one of the most popular flavors its consumption in the form of either vanilla extracts or vanillin is almost universal. 

Taste and Odor. The measurement of taste and odor is somewhat subjective and depends on the personal judgements of individuals. Panels of not less than five observers, and preferably more than ten, are used. The sample is diluted with odor-free water until a ratio at which the odor is just perceptible is determined this ratio is called the threshold odor number (TON). A similar method is used to detect a distinct taste in water (see Flavor characterization). ... 

Organic acids, including carbon dioxide, lower the wort pH during fermentation. The principal acids formed are lactic, pymvic citric, malic, and acetic acids, at concentrations ranging from 100—200 ppm. The main sulfur compounds formed during fermentation and thek perception thresholds are as follows H2S (5—10 ppb) ethanethiol (5—10 ppb) dimethyl sulfoxide (35—60 ppb) and diethyl sulfide (3—30 ppb). At low levels, these may have a deskable flavor effect at higher levels they are extremely undeskable. Sulfur dioxide also forms during fermentation, at concentrations of 5—50 ppm its presence can be tasted at levels above 50 ppm. 

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