Mentha Arvensis Oil

#### Mentha Arvensis Oil. The essential oil, steam distilled from the dried herb of **Mentha**** ****Arvensis**** **immediately prior to the inflorescence of the plant, is known in the U.S.A. as “**Mint**** ****Oil**” or **Cornmint**** ****Oil**”, while it is quite commonly called “peppermint oil” in other parts of the world. The latter term is definitely wrong and misleading. Only the plant mentha piperita (see monograph on **Peppermint**** ****Oil**) yields true peppermint oil. On the other hand, only in the U.S.A. is the control of production or import of **Mentha Arvensis Oil **sufficiently strict so that adulteration of true peppermint oil with “mint” oil is well-nigh impossible. This adulteration is extremely widespread in other parts of the world. There are several varieties of Mentha Arvensis, but the one which has attained greatest distribution is the variety **Piperascens**. The plant is found growing wild in China and parts of Japan, but is now cultivated on an enormous scale in Japan, Brazil, Formosa, less on the Chinese mainland, and on a smaller scale in Argentina, India, western Australia, the Union of South Africa, Angola, etc. Japan, Brazil and Formosa are the main producers. The annual world production of **Mentha Arvensis Oil **(i.e. total oil, before dementholization) is about 3,000 metric tons (1959, and has been increasing in spite of the very successful synthesis of **Menthol**** **from cheaper raw materials (piperitone, citronellal, and even pinene). The natural oil of mentha arvensis (forma piperascens) contains so much menthol that it will solidify at room temperature. By freezing the total oil, about 40% menthol is recovered, leaving the so-called “dementholized” oil which is liquid and still contains about *55%** *menthol. Part of this menthol, and most of the menthone in the dementholized oil can be further exploited by chemical treatment which converts the bitter- tasting menthone, a ketone, into various isomers of menthol. True 1-menthol can be isolated from the mixture, and the remainder can be sold as “liquid menthol”. Thus, the oil of mentha arvensis is mainly a starting material in the production of menthol, one of the most important of all flavoring agents. A wealth of information on the subject of cultivation of the plant, distillation of oil, isolation of menthol, etc. has been published during the past decades, and the author sees no need to repeat such information here. It should be noted, however, that there is a distinct difference in the chemical composition of the mentha arvensis oils of different origin: The Chinese oil contains about 2 percent esters, calculated as menthylacetate, the Brazilian contains from *5 *to 30 percent (in exceptional cases) of esters, and the Japanese mentha arvensis oil contains from 10 to 12 percent esters. The oil of **Mentha Arvensis **(dementholized) is a very common article exported from Japan, Formosa or Brazil. It is a pale yellow or almost colorless liquid of strong, fresh and somewhat bitter-sweet odor, to a certain degree reminiscent of the odor of peppermint oil. The undertone is somewhat harsh-woody and the dryout is bitterherbaceous. It produces a cool feeling on the mucous membranes in the nose and mouth cavities or upon direct contact with the skin. The flavor is cool, minty, somewhat rough and slightly bitter-green or sharp, less balsamic-herbaceous or sweet than the flavor of true peppermint. There is considerable difference in the organoleptic properties of the various types of mentha arvensis oil. It is hardly of any use, therefore, to mention a certain suggested use level or **Minimum**** ****Perceptible**. The oil is usually “bouquetted” prior to its use in flavors, see below. Various tests have been suggested to distinguish analytically between mentha arvensis oil and true peppermint oil (even the expert nose is not acknowledged in a court if it comes to a juridical discussion!). One of the best known tests is based upon a color reaction due to the presence of **Menthofuran **in true peppermint oil; this cumaron derivative is not present in mentha arvensis oil. Unfortunately, these analytical findings are not always used to the benefit of the product; they might even be used against the chemist analyst in attempts to fool him: A mixture of 15% true peppermint oil and 85% mentha arvensis oil will produce almost the same color reaction (with a slight difference in time and color shades) as would the pure peppermint oil. Even worse: this color reaction can be “introduced” in the mentha arvensis oil by the addition of foreruns from the rectification of true peppermint oil. Menthofuran is present in the fractions between the monoterpenes and the menthol, and peppermint oil is frequently submitted to fractional distillation in order to produce certain sweet types of peppermint oil for flavors, etc. The above mixture of peppermint oil (or fractions) and mentha arvensis oil will usually be revealed in an organoleptic test of the oil (sample) against a known and good peppermint oil. Modern instrumental analysis will, in most cases, also reveal such fraud. Mixtures of peppermint oil fractions with mentha arvensis oil are sold in Europe, Africa and Asia as “peppermint oil” with the further indication of standard quality such as “B.P.”, or “D.A.B. VI”, etc. or other Pharmacopoeias. “Quality”, at this point, refers to physico-chemical standards, not to odor or flavor. In brief, peppermint oil is one of the most adulterated essential oils in the trade outside the United States (see monograph on **Peppermint Oil**). **Mentha**** ****Arvensis**** ****Oil**** **finds extensive use in the flavoring of candy, e. g. chewing gum, hard candy, chocolate fillings, etc. and in all kinds of tooth- pastes, mouth washes, gargles, etc. Although more than 1,000 metric tons of menthol is isolated from crude “total” mentha arvensis oil per year (the crude oil is rarely sold commercially), the oil is still larger in quantity than the oil of true peppermint. Through skillful compounding (bouquetting) of selected fractions or of rectified mentha arvensis oil, the flavorist can create quite attractive artificial “peppermint — oils. As mentioned above, such oils will find use only outside the U.S.A. But the lower cost of dementholized mentha piperita oils will constantly tempt the suppliers to use this oil as a basis of their “special” peppermint oil (so-called). In 1946, when the Brazilian production and war-time leftover stocks of mentha arvensis oil hit an all-time high (over 1,000 metric tons), the price fell to about U.S. $ 0.70 per lb. (almost like citronella oil). Since the price of menthol (synthetic or isolated) at no time fell below about $ 5.00 per lb., it is quite understandable that the Brazilian producers abandoned plantations and distillations for many years thereafter. It could never be profitable to sell an oil with 55% menthol (the dementholized oil) at such low prices. It has become customary to use mentha arvensis oil as “peppermint oil” all over the world except in the U.S.A. In chewing gum, one of the main outlets of “peppermint oil”, the gum is often flavored with about one percent oil of mentha arvensis, while the sugar coating is flavored with 0.7 to 1.0 percent of a true peppermint oil. After a few “chews”, the customer is unable to identify the arvensis oil inside the gum because of the pleasant cooling and paralyzing effect of the good peppermint oil in the outer coating. See also **Peppermint**** ****Oil**.