Esters organoleptic properties

The organoleptic properties of black tea depend to a considerable extent on the astringency resulting from the interaction of caffeine with the oxidized galloyl ester of the flavanols. The aroma components of black tea also constitute a unique flavor profile that blends well with the taste of the nonvolatile materials. The caffeine provides a moderate level of stimulation, which adds further to the appeal of the beverage, although tea has been shown to provide relaxation as well as revival of character.119... 

In comparison with the araliphatic alcohols discussed in Section 2.5.2, very few phenol alcohols are used as fragrance and flavor materials. Neither the alcohols corresponding to vanillin, ethylvanillin, and heliotropin nor their esters have special organoleptic properties. Anise alcohol and its acetate are the only products that are used to some extent in perfume and aroma compositions. 

After approx. 48 h of fermentation, the fermented mash shows an alcohol content of approx. 6-10% by vol. When distilled in continuous stills with 3 or more colunms, the alcohol level in the distillate can be enriched up to 96.6% by vol. The purification of the raw distillate is normally carried out in continuous rectification equipment, for which the raw alcohol is usually diluted to approx. 15% by vol. before rectification in order to better separate fusel oil components. The first fractions of the rectified distillate - the so-called head fraction - contain significant quantities of acetaldehyde, methyl alcohol and low-boiling esters the middle part - heart fraction - represents so-called neutral spirits with an alcohol content of approx. 96.6% by vol. The tail fractions contain higher alcohols and higher esters etc. Since head and tail fractions contain organoleptic properties undesirable for neutral alcohol, they usually are employed as technical alcohol or have lately also been isolated and used as starting raw materials for the production of natural aroma components. 

Organoleptic Properties. Stereochemical differences of enantiomeric excipients may influence perception by sensory organs. Kutti [17] reported as early as 1886 that the interaction of stereoisomer with chiral receptors led to chiral discrimination as a consequence of the formation of diastereomers. He observed that the dextrorotatory asparagine has a sweet taste whereas the levorotatory form is tasteless. Greenstein and Winitz [18] and Solms et al. [19] reported such differences for many amino acids. Shallenberger et al. [20] reported that for some monosaccharides, both isomers have similar sweetness. In contrast, aspartame (A-aspartylalanine methyl ester) is marketed as the l,l isomer because it is more than 100 times as sweet as sucrose. However, the l,d diastereomer of aspartame is bitter [11], It should be noted that the individual differences of perception of these properties could vary. 

Dipeptides and Polymeric Di- and Tripeptides. Aspartame is a polymeric dipeptide with a specific rotation of -1-14.5° to -1-16.5° [68]. Stereoselective differences in organoleptic properties of aspartame have been documented. Methyl esters of some dipeptides such as alanylalanine and tryptophylalanine have been reported to interact stereoslectively with p-CD. Since these peptides can serve both as active ingredients and as excipients, possible chiral excipient irug or exdpient xdpient interaction should be investigated. 

Composition Genuine essential oils consist exclusively of volatile components with boiling points mainly between 150 and 300 °C. They contain predominantly hydrocarbons or monofunctional compounds such as aldehydes, alcohols, esters, ethers, and ketones. Parent compounds are mono- and sesquiterpenes, phenylpropane derivatives, and longer-chain aliphatic compounds. Accordingly, essential oils are relative non-polar mixtures, i.e., they are soluble in most organic solvents. Often the organoleptic properties are not determined by the main components but by minor and trace compounds such as, e.g., 1,3,5-undecatrienes and pyrazines in galbanum oil. In many of the commercially important oils, the number of identified components exceeds 100. Very many of the constituents are chiral, frequently one isomer predominates or is exclusively present, e. g., (- )-menthol in peppermint oils or (-)-linalyl acetate in lavender oil. 

Volatile fatty acid homologs higher than acetic acid have not been found as natural products of woody plants, although such acids and their esters are important components that contribute to the organoleptic properties of fruits. Nevertheless, propionic, butyric, valeric, and caproic acids occur in wetwood, in addition to elevated levels of acetic acid, as anaerobic fermentation products of starch (34, 36, 37, 43). For example, the concentration of acetic, propionic, and butyric acids of 0 to 3 mM in normal sapwood of white fir increases to as much as 38, 55, and 23 mM, respectively, in the wetwood of some fir species (38). The volatile fatty acids in gum turpentine and in the low wine (the aqueous phase of turpentine distillation) and turpentine tailings (24) also are likely the product of anaerobic fermentation. However, it should be noted that the oleoresin turpentine from Pinus sabiniana consists primarily of -heptane (22), and the turpentine from R jeffreyi contains a significant proportion of -heptane (22) and smaller amounts of A2-pentane, nonane, and undecane (39). The -heptane is derived not through the mevalonate pathway but rather by decarboxylation of octanoic acid (32). Presumably, the other hydrocarbons are also formed by decarboxylation. 

The organoleptic properties of some esters, which are important components of fruits, spices and fragrant flowers, are given in Table 8.25. One of the most important reactions of esters is... 

With improved analytical methods there has been a large increase in the number of compounds identified in wines. Volatile compounds from different families (such as alcohols, esters, aldehydes, terpenes, etc.) play an important role in the organoleptic characteristics of wines. This wide variety of compwimds with different chemical properties and with different concentrations makes the flavour pa-ofile of wines very complex. Therefore, it is necessary to standardise the terminology so as to facilitate the knowledge of the aromatic profile of wines. 

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