Cooling effect, of menthol

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). 

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... 

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. 

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. 

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. 

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. 

Chemesthesis. The term chemesthesis has been introduced to classify thermal and painful sensations experienced in the mouth (26). Chemesthesis refers to a chemical sensibility (mouthfeel) in which certain chemicals direcdy activate nerve fibers at the level of the basal membrane in the mouth. The sensations are analogous to similar effects at the skin surface where there is a close anatomical and functional relationship. Sensations include the "hot" of capsaicin and piperine, which are active components of chili and pepper, the coolness of menthol and the irritation of chemicals such as salt at high concentrations [FIGURE 4]. Some of the descriptive terms used to make qualitative distinctions in food sensations include pungency, freshness, tingling, burning and sharpness. 

Although cyclic terpene alcohols occur widely in nature, few have the physiological properties that make them important fragrance or flavor materials. Exceptions are a-terpineol and (—)-menthol, the latter because of its cooling/refreshing effect. Of the bicyclic monoterpene alcohols, bomeol deserves mention. 

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... 

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. 

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... 

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