Sensory compounds

It is well known for example in the saturated LDPE polymer chains that a certain number of double bounds exist which can be measured with IR spectroscopy. By extraction with non-polar solvents and GC separation, numerous alkanes and alkenes can be identified which are dissolved in small concentrations in the PE. The odor thresholds of these compounds are in general so high that these hydrocarbons play no sensory role. As a result no correlation can be made between the total amount of volatile compounds isolated from PE or the fingerprint chromatogram from a GC separation and the sensory properties of a sample. The relevant sensory compounds as a rule are the (order of magnitude) less concentrated oxygenated compounds in the... 

Another approach for the development of PET-based molecular indicators for detection of nerve agents utilizes phosphorylation of an amine functionality, which is integrated into the structure of a fluorophore. This principle is used in the case of highly substituted anthracene bisimide (Figure 16.17f) [51] and fluoresceinamine (Figure 16.17g) [52]. These sensory compounds can be easily incorporated into polymer matrices [51] or deposited onto the surface of silica beads [52], thus yielding solid state detectors. 

For analysis of free compounds, the headspace analysis with a multiphase fiber is even more interesting and less time-consuming. This approach can replace the majority of the quantification of free compounds measured by SPE techniques, considering also the possibility of the sampling automation using a GC-MS system which can be coupled to a statistical treatment of fragments abundance (Kinton et al., 2003 Cozzolino et al., 2006). Moreover, HS-SPME/GC-MS is a very effective and efficient method to analyze specific compounds present in trace levels at about ppt level, because they can be better and selectively enriched in the headspace. This method is employed nowadays to quantify some important and peculiar sensory compounds such as ethyl and vinylphenols, pyrazines, cork off-flavour substances (TCA, etc.) and other contaminants such as geosmine (Riu et al., 2002 Chatonnet et al., 2006) and, as shown below, sulphur volatiles. 

Macpherson LJ, Hwang SW, Miyamoto T, Dubin AE, Patapoutian A, Story GM (2006) More than cool promiscuous relationships of menthol and other sensory compounds. Mol Cell Neurosci 32(4) 335 3... 

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. 

The development of precise and reproducible methods of sensory analysis is prerequisite to the determination of what causes flavor, or the study of flavor chemistry. Knowing what chemical compounds are responsible for flavor allows the development of analytical techniques using chemistry rather than human subjects to characterize flavor (38,39). Routine analysis in most food production for the quaUty control of flavor is rare (40). Once standards for each flavor quaUty have been synthesized or isolated, they can also be used to train people to do more rigorous descriptive analyses. 

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. 

Table 2 Hsts examples of compounds with taste and their associated sensory quaUties. Sour taste is primarily produced by the presence of hydrogen ion slightly modified by the types of anions present in the solution, eg, acetic acid is more sour than citric acid at the same pH or molar concentration (43). Saltiness is due to the salts of alkaU metals, the most common of which is sodium chloride. However, salts such as cesium chloride and potassium iodide are bitter potassium bromide has a mixed taste, ie, salty and bitter (44). Thus saltiness, like sourness, is modified by the presence of different anions but is a direct result of a small number of cations.

The relationship between molecular stmcture and sensory properties is very unclear for compounds with odor. It seems likely that there is a set of odors that could be called primaries, but a widely accepted Hst of such primary odor quahties has not been devised. Molecular size and shape have been used to... 

Several manuals devoted, at least in part, to flavor formulation have been published (52—63), eg, literature from the Fragrance Materials Association of the United States, Washington, D.C. The increasing number of materials available has resulted in the improvement of flavor characteristics and has permitted a closer rendition of natural flavors. Often such materials bear a scant sensory relationship to the tme natural flavor character. When used as a component and judiciously applied, these materials serve a useful purpose in a properly compounded flavor. 

The flavor chemist is responsible for the basic knowledge of sensory and appHcation properties of each of this large number of raw materials the large number of possible combinations of these items to produce specifically flavored finished compounds is readily apparent. It is not uncommon to develop a flavor that combines essential oils, plant extractive, fmit juices, and synthetics. The choice of materials depends on type of product, conditions of manufacture, labeling, and intended use. 

Advances in the technology of chemical analysis and the abiUty to analy2e for trace amounts of complex compounds now make it possible to combine analytical information with sensory analysis to identify taste characteristics and faciUtate process control. 

The function of a sensory system is to select suitable modalities from the multitude presented by the environment, and translate them into corresponding modalities of sensory information that are then projected and processed into the various parts and finally submitted to the central processing-unit, the brain. A working hypothesis of the mechanism by which the taste system senses chemical compounds is that macromolecules that are... 

An additional and widespread neuroactive (transmitter-like) compound is nitric oxide (NO). This gaseous secretion is a product of the action of the enzyme NO-synthase on arginine. It is implicated in at least two roles within the non-sensory tissues of the organ, and at particular synapses in the AOB. One nitric oxidergic effect is initiated by the nerve fibres supplying the smooth muscle component of the vasomotor tissues. The other effect is the expected action of NO on the output... 

TRPV1 is a nonselective cation channel predominantly expressed in sensory neurons and activated by capsaicin, heat (>42°C), pH (<5.4), and noxious stimuli. Several compounds have advanced into clinical development and have been extensively covered in recent reviews [5,34—39]. Among these, MK-2295 (structure not disclosed), AMG 517 (38), SB-705498 (39), and GRC-6211 (structure not disclosed) have reportedly encountered safety issues [35]. In phase II clinical trials with MK-2295, patients experienced an increase in core body temperature... 

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