Menthol cooling effect

The metallic taste (12,19,20) is not ascribed to any special taste buds or mouth area. Along with pungency (the hot taste of peppers), astringency (the puckering taste of alum), and cold taste (the cool effect of menthol), the metallic taste is called a common chemical sense (21). 

Menthol Manufacture. Of the menthol isomers, only (-)-menthol [2216-51 -5] and (+)-menthol [15356-70-4] are of commercial importance. The most important natural sources of (—)-menthol are the oUs of Mentha arvensis (75—90%) and Mentha piperita (50—65%). The main suppUers ate Japan, China, BrazU, and Taiwan for the former and the United States, CIS, Bulgaria, and Italy for the latter. (—)-Menthol is known for its refreshing, diffusive odor characteristic of peppermint. It also is known for its strong physiological cooling effect, which is useful in cigarettes, dentifrices, cosmetics, and pharmaceuticals. 

Camphor is a rubefacient—it relieves mild pain and itching, and creates inflammation and redness when rubbed into the skin. Much like menthol, it has a cooling effect when applied to the skin. 

Physical Properties. The eight optically active menthols differ in their organoleptic properties [77]. (-)-Menthol has a characteristic peppermint odor and also exerts a cooling effect. The other isomers do not possess this cooling effect and are, therefore, not considered to be refreshing. ( )-Menthol occupies an intermediate position the cooling effect of the (-)-menthol present is distinctly perceptible. 

For instance, (-)-menthol (p-menthan-3-ol) is one of the most important flavouring agents and is the major compound in natural peppermint oil. The characteristic peppermint odour and the typical cooling effect is limited to (-)-men-thol. The other isomers do not show this refreshing effect. A racemic mixture of menthol holds an intermediate position the cooling effect is still perceptible. 

Menthol 0.003-0.015% in suspensions, and syrups Cooling effect Sublimes easily above 25° C and composition of natural oil may vary with source Incompatible with thymol, phenol, camphor, and other excipients Slightly soluble in glycerin very soluble in alcohol... 

Another important taste sensation is coolness, which is a characteristic of menthol. The cooling effect of menthol is part of the mint flavor complex and is exhibited by only some of the possible isomeric forms. Only (-) and (+) menthol show the cooling effect, the former to a higher degree than the latter, but... 

America, and Japan. The main constituents of the essential oil are a- and p-pinene, limonene, cineol, ethyl amylcarbinol, menthone, menthol, isomenthol, menthyl acetate, and piperitone. It has a strong mint odor with a sweet balsam taste masked by a strong cooling effect. It is widely used in foods, as well as in liquid pharmaceuticals, to 8000 ppm. 

Menthol is widely used in pharmaceuticals, confectionery, and toiletry products as a flavoring agent or odor enhancer. In addition to its characteristic peppermint flavor, /-menthol, which occurs naturally, also exerts a cooling or refreshing sensation that is exploited in many topical preparations. Unlike mannitol, which exerts a similar effect due to a negative heat of solution, /-menthol interacts directly with the body s coldness receptors. d-Menthol has no cooling effect, while racemic menthol exerts an effect approximately half that of /-menthol. 

Appearance colorless, prismatic or acicular, shiny crystals, without the characteristic odor, taste, and cooling effect of /-menthol. The crystalline form may change with time owing to sublimation within a closed vessel. 

Camphor is a good example of the importance of the mode of application for the cutaneous effect. If camphor is massaged intensely in the skin the result will be an erythema, but if it is spread out carefully and lightly, a cooling effect is obtained, similar to the effect of menthol. Furthermore, camphor has a local anaesthetic effect. 

The three most important cyclic monoterpenoids are 1-menthol, 1-carvone and a-terpineol (including its esters). 1-Menthol occurs in a number of mint oils and is used not only for its minty odour, but also, and more importantly, for its physiological cooling effect. Its chemistry is of such interest and significance that it warrants a section of its own, which will be found at the end of this one. 

Menthol (1-methyl-4-isopropylcyclohexan-3-ol) is a monocyclic monoterpenoid, which possesses three asymmetric carbon atoms and therefore exists in eight stereoisomeric forms as shown in Figure 4.23. 1-Menthol is the most highly desired of these since it produces a physiological cooling effect. That is, when applied to skin or mucus membranes, 1-menthol creates the sensation of cooling independent of the... 

One optical isomer that you might have used is L-menthol. This natural isomer has a strong, minty flavor, and a cooling odor and taste. The mirror-image isomer, D-menthol, does not have the same cooling effect as L-menthol. 

Menthol, used because of its cooling effect, is a rare sensitizer (Papa and Shelley 1964 Camarasa and Alomar 1978), but has caused dermatitis, cheilitis, and stomatitis. 

Interestingly, not only low temperatures cause the opening of this ion channel, but also substances like (-)-menthol. This binds to the TRPM8, opens the ion channel, and thereby simulates coldness, although there is no change in temperature. It is noteworthy that (+)-menthol binds to the receptor as well, but its cooling effect reaches only 25 % compared to the enantiomer. 

Cineole interacts with TRPM8, the cool sensitive thermoreceptor that is primarily affected by menthol. In comparison to menthol, the effect of 1,8 cineole on TRPM8 (as measured by Ca in ux kinetics) is much slower and declines more rapidly (Behrendt et al., 2004). In a similar manner to menthol, the antitussive activity of 1,8-cineole may be due in part to its stimulation of airway cold receptors. 

Humans were able to differentiate the odors of the (-I-) and (—) enantiomers of a-pinene, carvone and limonene but failed to differentiate between (-1-)- and (—)-menthol. Both menthol enantiomers have a peppermint odor quality but (—)-menthol has a much stronger cooling effect than (-i-)-menthol [25]. S-(—)-limonene has a turpentine odor impact and R-(-i-)-limonene an orange odor impact [25]. Neomenthol, isomenthol, and neoisomenthol do not present a cooling effect. 

Because of the presence of three asymmetric C-atoms in its structure, menthol occurs in four pairs of optical isomers, (—)- and (+)-menthol, (+)- and (—)-neomenthol, (+)- and (—)-isomenthol, and (+)- and (—)-neoisomenthol. (—)-Menthol is the isomer that mostly occurs in nature and, besides its characteristic odor, it possesses a cooling effect on the skin and mucosa. It can be obtained synthetically or from peppermint or other mint oils, or from essential oils such as citronella oil, eucalyptus oil, and Indian turpentine oil. Due to its minty smell and flavor, it is used in pharmaceuticals, soaps, hygiene products like toothpaste, cosmetics, chewing gum, teas, sweets, and tobacco products [40, 41]. 

The cooling effect and tingling sensation of menthol by topical application is related to its stimulation of cold-receptors. This stimulation is caused by inhibiting Ca -currents of neuronal membranes, since Ca -channel blockers are connected to painkilling properties [40]. Both (-1-)- and (-)-menthol show equiactive local anesthetic activity, but only (—)-menthol also elicits an analgesic effect [40]. 

The terpene alcohol (—)-menthol is an important flavoring substance because of its unique cooling effect and flavor. (—)-Menthol is used in toothpastes, cosmetics, and in pharmacy and medicine because of its anastatic properties, for example, for contact urticaria and treatment of headache or bronchitis. Another major user is the tobacco industry with a share of 25%. 

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