Fragrance compounds, complexity

The smell and taste of plants rely on aroma and fragrance compounds, many of which (besides fhe terpenoids) are derived from phenylpropanoid metabolism. In food and cosmetic industry, such fragrance and aroma compounds play an important economical role. Simple phenolic fragrance compounds are, e.g., eugenol, isoeugenol or (methyl)chavicol (Fig. 4.2), the biosynthesis of which has been clarified recently more complex compounds are phenolic esters. Evolutionary aspects of the bios)mthesis of flavours and scents have been reviewed by Gang (2005). 

There is an increasingly widespread use and exposure to scented products. Fragrances are complex mixtures of primarily volatile compounds that influence both indoor and outdoor air quality. In order to detect an odour, molecules of the substance must be airborne. Once in the air, they break down, mix with other pollutants, and form other compounds that often are more irritant or allergenic than the original substance (Bridges 2002). Fragrances such as air fiesheners are used in products to scent the environment. They are added in large amounts to toiletries, cosmetics, household products, and a wide variety of other consumer products. 

Epoxides are well known as one of the most valuable intermediates to produce commercially important chemicals such as polyglycols, polyamides, polyurethanes and so many other polymers, chiral pharmaceuticals, pesticides, detergents, agrochemicals, food additives, dyestuffs, flavor and fragrance compounds, surfactants, antistatic agents, corrosion protection agents, textiles, non-toxic PVC plasticizers and stabilizers. They are also valuable additives to lubricants and adhesives. In the last decade, several soluble Schiff base complexes of Cr, Mo, Re, Ni, Co, Mn, V, Cu, Ru, and Ti have been employed as active homogenous catalysts in epoxidation of alkenes. 

GC using chiral columns coated with derivatized cyclodextrin is the analytical technique most frequently employed for the determination of the enantiomeric ratio of volatile compounds. Food products, as well as flavours and fragrances, are usually very complex matrices, so direct GC analysis of the enantiomeric ratio of certain components is usually difficult. Often, the components of interest are present in trace amounts and problems of peak overlap may occur. The literature reports many examples of the use of multidimensional gas chromatography with a combination of a non-chiral pre-column and a chiral analytical column for this type of analysis. 

The number of synthetically produced fragrance and flavor chemicals has since expanded continually as a result of the systematic investigation of essential oils and fragrance complexes for odoriferous compounds. Initially, only major components were isolated from natural products their structure was then elucidated and processes were developed for their isolation or synthesis. With the development of modern analytical techniques, however, it became possible to isolate and identify... 

The odors of single chemical compounds are extremely difficult to describe unequivocally. The odors of complex mixtures are often impossible to describe unless one of the components is so characteristic that it largely determines the odor or flavor of the composition. Although an objective classification is not possible, an odor can be described by adjectives such as flowery, fruity, woody, or hay-like, which relate the fragrances to natural or other known products with similar odors. 

C13H22O2, Mr 210.32 is a mixture of isomers, bpo kPa 102 °C, ng 1.4626, a colorless to pale yellow liquid with rosy, spicy, fruity, and woody odor. For its preparation 3,6-dimethyl-6-hepten-2-one and 7-methyl-6-octen-3-one are treated with ethyl diethylphosphoryl acetate to give a mixture of octadienoic acid esters. Cyclization with sulfuric/formic acid yields the title compounds as a mixture with isomers [134]. With its complex odor picture it is used in fine fragrances for shading. 

Standardization of specifications for complex fragrance and flavor materials, such as essential oils and absolutes, is far more difficult than for single compounds. 

The recovery of flavors and fragrances from diluted aqueous streams may be of industrial interest under different circumstances (1) recovery of complex aroma profiles and/or target aroma compounds from active biocatalytic processes (2) recovery of complex aroma profiles and/or target aroma compounds from natural extracts and industrial processes aqueous streams. Pervaporation offers a unique solution for the recovery of complex aroma profiles. An example for the recovery of complex aroma profiles, faithful to their origin, is the recovery of a muscatel aroma from an ongoing wine-must fermentation [31, 32]. 

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