Aroma esters

Suomalainen, H. (1981) Yeast esterases and aroma esters in alcoholic beverages. Journal of the Institute of Brewing, 87, 296-300. 

Mengual et al. have observed an Arrhenius type of dependence of the permeate flux on the feed temperature. An increase in the feed circulation velocity increases the heat transfer coefficient in the liquid boundary layer, which in turn increases the VMD flux due to the reduction in the temperature polarization. Concentration factors increased with a decrease in feed temperature during VMD, and for a decrease of 30°C to 10°C, increase in concentration factors from 7-15.5 to 21-31 were obtained for a highly volatile black currant aroma ester [17]. 

In addition to diacetyl, O. oeni produces esters, flavor compounds also important for wine flavor and aroma. Esters are primarily produced by Saccharomyces during alcoholic fermentation (Mason and Dufour, 2000 Nykanen, 1986 Nykanen and Nykanen, 1977 Soles et al., 1982), although evidence shows that esters such as ethyl acetate, ethyl lactate, ethyl hexano-ate, and ethyl octanoate can be synthesized by O. oeni (De Revel et al., 1999 Delaquis-Pascal et al., 2000 Edwards and Peterson, 1994 Maicas et al., 1999 Tracey and Britz, 1989). For example, Edwards and Peterson (1994) reported that strains of O. oeni synthesized relatively large amounts of ethyl lactate (183-1280 /ig/L) during growth in microbiological medium. In agreement, Maicas et al. (1999) reported that 50 mg/L of ethyl lactate was produced in wines fermented with O. oeni, as well as isoamyl acetate and ethyl caproate, compounds important for a pleasant fruity note in wine (Gil et al., 1996 Mason and Dufour, 2000 Nykanen, 1986). 

Ueda Y, Tsuda A, Bai JH, Fujishita N, Chachin K (1992) Charateristic pattern of aroma ester formation from banana, melon, and strawberry with reference to the substrate specificity of ester synthetase and alcohol contents in pulp. Nippon Shokuhin Kogyo Gakkaishi 39 183-187... 

Many esters occur naturally Those of low molecular weight are fairly volatile and many have pleasing odors Esters often form a significant fraction of the fragrant oil of fruits and flowers The aroma of oranges for example contains 30 different esters along with 10 carboxylic acids 34 alcohols 34 aldehydes and ketones and 36 hydrocarbons... 

Aroma chemicals are isolates, or chemically treated oils or components of oils. Some components are removed physically, others chemically. In most cases, they are further purified by distillation. For example, Bois de Rose (rosewood) oil may be distilled to isolate linalool, which may be then further treated chemically to yield derivatives such as linalyl acetate, an important fragrance ingredient and a primary component in its own right of lavender and lavandin oils. Vetiver oil Haiti, although containing only 70% alcohols, is treated with acetic anhydride, then carefully distilled to include valuable odor components in the distillate, even though they may not be esters. 

Isoamyl saUcylate is perhaps the most important ester of saUcyhc acid for perfumery purposes. Generally, it is manufactured by the transesterification of methyl saUcylate. It has a characteristic flowery aroma and is useful in soap fragrances. The May 1996 price was 5.30/kg (18). Other saUcylates of commercial interest as flavor and fragrance agents include isopropyl, isobutyl, phenethyl [87-22-9] and 2-ethyIhexyl saUcylates. 

Volatiles or Aroma. The essential oil, or aroma, of tea provides much of the pleasing flavor and scent of green and black tea beverages. Despite this, volatile components comprise only - 1% of the total mass of the tea leaves and tea infusions. Black tea aroma contains over 300 characterizing compounds, the most important of which are terpenes, terpene alcohols, lactones, ketones, esters, and spiro compounds (30). The mechanisms for the formation of these important tea compounds are not fully understood. The respective chemistries of the aroma constituents of tea have been reviewed... 

Garyophyllene. (-)-CaryophyUene can be isolated from Indian turpentine and has been used to prepare a number of woody aroma products. The epoxides are produced by reaction with peracids. Acetylation of caryophyUene also gives a usehil methyl ketone (180) (Fig. 8). Acid-catalyzed rearrangement of caryophyUene in the presence of acetic acid gives a mixture of esters, which are related to caryolan-l-ol and clovan-2-ol (181). 

Longifolene. There are at least four commercially important aroma chemicals made from (+)-1ongifo1ene and about thirteen products made from (-)-isolongifolene (90) (182). Acetoxymethyl longifolene or the formate are formed during the Prins reaction on (+)-1ongifo1ene. Saponification of the esters gives the useful perfumery alcohol (183) (Fig. 9). 

Phenyl-2-propenoic acid [621 -82-9] commonly referred to as cinnamic acid, is a white crystalline soHd having a low intensity sweet, honeylike aroma. It has been identified as a principal constituent in the botanical exudates from Styrax IJquidamber orientalis) Benzoin Styrax ben in Pern Balsam [Myroxylon pereirae and Tolu Balsam (]Ayro>ylon balsamum) (4,5). In these, as well as numerous other natural products, it exists both as the free acid and in the form of one or more of its esters, as for example, methyl cinnamate, ben2yl cinnamate [103 1 -3] and cinnamyl cinnamate. 

Methylpyrazine reacts with sodamide in liquid ammonia to generate the anion, which may be alkylated to give higher alkylpyrazines (Scheme 10) (61JOC3379). The alkylpyrazines have found extensive use as fiavouring and aroma agents (see Section 2.14.4). Condensation reactions with esters, aldehydes and ketones are common, e.g. methyl benzoate yields phenacylpyrazine in 95% yield, and reactions of this type are summarized in Scheme 11. 

Stereoanalysis of 2-alkyl-branched acids, esters and alcohols in apple aroma concentrate... 

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... 

Possible differences are also well illustrated by 3-thio- and 3-methyl-thiohex-anols and their esters (Table 1). Among these compounds, there is a tendency for the (R) enantiomers to have a typical, fruity aroma. However, for 3-methylthiohexanol (an aroma component of yellow passion fruit) this situation is reversed the (S) enantiomer had the characteristic fruity aroma ( exotisch, fruchtig ).52 For the separation of enantiomers of odorous compounds, enan-tioselective GLC with chiral stationary phases, and MGDC techniques using a conventional capillary column and an enantioselective column are commonly used.53... 

Benzisoxazolone couplers, 19 254 Benzisoxazolone dye releasers, 19 290 Benzoate esters, 10 513-513 aroma chemicals, 3 257 Benzoate plasticizers, 25 184 Benzoates... 

Benzylic esters, aroma chemicals, 3 256 Benzylideneacetone, 3 595 4,6-O-Benzylidene-D-glucopyranose,... 

Decalyl esters, aroma chemical derived from naphthalene, 3 235 Decamethylene diisocyanate,... 

Holograms, silver and, 22 639, 657-658 Holographic applications, spectrally sensitized materials for, 9 519 Holographic interferometry, 19 588-589 Holography, optical, 27 421 Holst, Axel, 25 747 Homatropine hydrobromide, 4 360t Homatropine methylbromide, 4 360t Home desalinators, 26 55 Home scrap, 23 261, 262 Home water softeners, 22 818-819 Homobenzoate esters, aroma chemicals, 3 257... 

Continuing with this theme, if we extend the alcohol part of the ester to five carbon atoms, to get pentyl butyrate and the aroma of apricots ... 

Here are some additional examples of esters as aromas or flavors propyl acetate is the aroma of pears pentyl acetate is the aroma of bananas octyl acetate is that for oranges. 

Here too we have a common contributor to the acid component of an ester, acetic acid in this case, coupled to various alcohol components to yield a variety of distinct biological responses, the aromas of different fraits. 

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