Volatile esters

Essential oils are obtained from fmits and flowers (61,62). Volatile esters of short- and medium-chain carboxyHc acids or aromatic carboxyHc acids with short- and medium-chain alcohols are primary constituents of essential oils, eg, ethyl acetate in wines, brandy, and in fmits such as pineapple ben2yl acetate in jasmine and gardenia methyl saHcylate in oils of wintergreen and sweet birch. Most of these naturally occurring esters in essential oils have pleasant odors, and either they or their synthetic counterparts are used in the confectionery, beverage, perfume, cosmetic, and soap industries (see Oils, essential). 

Eau de Cologne perfume is made from about 80-85 per cent water and 12-15 per cent ethanol. Volatile esters make up the remainder, and provide both the smell and colour. 

Charentais cantaloupe melon Cucumismelo L. var. cantalupensis Naud.) was characterised by abundant sweetness and a good aromatic flavour [68]. The aroma volatiles of Charentais-type cantaloupe melons, as with other cantaloupes, comprise a complex mixture of compounds including esters, saturated and unsaturated aldehydes and alcohols, as well as sulfur compounds [26, 65]. Among these compounds, volatile esters were quantitatively the most important and therefore represent key contributors to the aroma [68]. The linear saturated and unsaturated aldehydes seem to originate from the degradation of linolenic and linoleic acids [26, 32, 33, 67]. 

Scheme 26.3 Biosynthesis of volatile esters catalysed by alcohol acyltransferases. SAAT strawberry alcohol acyltransferase, VAAT Pragaria vesca alcohol acyltransferase, ATFl, AFT2 Saccharomyces cerevisiae alcohol acetyltransferases, BanAAT banana alcohol acyltransferase...

Among the compounds commonly determined in research laboratories are diacetyl, 2,3-butandiol, glycerol, citramalic acid, amino acids (especially proline), histamine, ammonia, succinic acid, phosphate, ash, alkalinity of the ash, ethyl, acetate, methyl anthranilate, total volatile esters, higher alcohols (both total and individually) phenolic compounds, etc. An elegant method for determining ethyl esters, capronate, caprylate, caprinate, and laurate using carbon disulfide extraction and GLC has been published (123). 

Nordstrom, K., Studies on the Formation of Volatile Esters in Fermenta-... 

As always in the analysis of milk fat, the short chain fatty acids cause problems. A major difficulty has not been the GLC separation of these acids but their transfer from the esterification mixture to the GLC instrument without loss of the volatile esters. A widely used procedure is a slight modification of the method developed by Chris-topherson and Glass (1969) which uses sodium methoxide for transesterification. This technique can be employed with other fats, but not with those containing appreciable amounts of free fatty acids where HCl-methanol is required. 

Data from analyses of air samples in Lavy s 2,h,5-T study (15, 19) and 2,L-D study (20) indicate that exposure via inhalation was insignificant during application of low volatile ester formulations of these herbicides. 

No direct measurements of volatilization losses of any pesticide has been made following applications to forests. However, Grover et al. (7) recently measured the volatilization of 2,4-D after application as the isooctyl ester to a wheat field. This same low-volatile ester is used in forest vegetation control. The total vapor loss within 3 days after application of the isooctyl ester of 2,4-D was 20% of the amount applied. The applicability of these findings to volatilization of like pesticides in the forest environment will be discussed. We will indicate how volatilization in forests may differ from that reported from agricultural applications to open fields. The paper also will discuss the transfer of pesticides into the atmosphere from the standpoint of mechanisms involved, factors influencing rates of... 

The length of time pesticides persist in the forest floor and soil bears strongly on the probability they will be lost by volatilization (28-31). The phenoxy herbicides are commonly applied to forests as the low-volatile esters. These esters are readily hydrolyzed to their respective acids in soil or on the forest floor. For example, Smith (32) reported that no traces of 2,4,5-T and 2,4-D esters were observed in any of four moist soils after 48 and 72 hours, respectively, and most of them were hydrolyzed in less than 24 hours. The vapor pressures of the acids are much lower than the esters and this hydrolysis, along with subsequent degradation of the acids, results in a very low potential for volatilization of these materials from soil. 

To a large extent, therefore, the toxicities of esters tend to be those of their hydrolysis products. Two physical characteristics of many esters that affect their toxicities are relatively high volatility, which promotes exposure by the pulmonary route, and good solvent action, which affects penetration and tends to dissolve body lipids. Many volatile esters exhibit asphyxiant and narcotic action. As expected for compounds that occur naturally in foods, some esters are nontoxic (in reasonable doses). However, some of the synthetic esters, such as allyl acetate, have relatively high toxicities. As an example of a specific toxic effect, vinyl acetate acts as a skin defatting agent. 

During mead fermentation, several problems are generally encountered. For example, the anticipated alcohol content may not be achieved within the time desired. There may also be a lack of uniformity in the final product, due to differences in water content of the honey used. In some situations, such as worts with high sugar contents, successive addition of honey is needed to avoid premature termination of fermentation. This likelihood of stuck fermentation is increased as most mead is made empirically, without adjustments. This can lead to subsequent yeast refermentation and secondary fermentations by lactic and acetic acid bacteria. These can undesirably increase acidity and the production of volatile esters (Casellas, 2005). The presence of these compounds alters... 

Esters formed during heating of lipids are contributors to pork flavor. Raw pork contains only a small number of esters, while cooked pork contains significantly more, and acetates are the most prominent volatiles. Esters of cooked pork are derived from C1-Ci0 acids, which impart a fruity sweet note to pork meat (J16). Beef contains a higher proportion of esters derived from long chain fatty acids which possess a more fatty flavor character (16). The characteristic odor of mutton is believed to be due to the evolution of 4-methyloctanoic acid, 4-methylnonanoic acid and similar compounds during heating (17). 

Table 15.6. Newly identified volatile ester components in Bourbon vanilla beans and their sensory impressions.

The important thing concerning volatility at various temperatures is the relative amount of material in the atmosphere at the different temperatures. If one knows the latent heat of vaporization, the tendency of the material to vaporize can be calculated from Equation 3. If we now consider preparations of derivatives whereby vapor loss can be reduced, it is immediately apparent that the latent heat of vaporization must be increased. This can be done with the phenoxyacetic acid compounds in preparing the so-called low volatile esters as represented by the butoxy-ethanol ester as illustrated in Table II. Determinations of the ratio of the latent heat of vaporization of the butoxyethanol ester to that of the isopropyl ester indicated a value of about 2. 

Small molecule carboxylates are an important class of compounds that plants produce to attract pollinators,44 defend against herbivory,45 7 regulate the cell cycle,48,49 and induce defense responses.50 5 Often these compounds are esterified and volatilized. Plants utilize the emission of volatile esters as chemoattractants and signaling molecules. Classes of volatile compounds include the salicylates and jasmonates, which are ubiquitously distributed in the plant kingdom. Jasmonic acid, salicylic acid, and their methyl ester derivatives, are intimately involved in cell regulation and help control such developmental processes as seed germination, flower development, fruit development, and senescence.14,17,53... 

Originally isolated and characterized from the petals of Clarkia breweri, salicylic acid carboxyl methyltransferase (SAMT), converts salicylic acid to methylsalicylate.14 Methysalicylate, a volatile ester, has a characteristic wintergreen scent Apart from its putative role in defense, methylsalicylate is an important chemoattractant for moth-pollinated flowers and one of the main volatiles released from Clarkia breweri flowers.44,55 SAMT is a member of the type 3 family of plant MTs. Similarly to the previously discussed families of methyltransferases, type 3 MTs are homodimeric proteins. 

MURFITT, L. M., KOLOSOVA, N., MANN, C. J., DUDAREVA, N Purification and characterization of S-adenosyl-L-methionine Benzoic acid carboxyl methyltransferase, the enzyme responsible for biosynthesis of the volatile ester methyl benzoate in flowers of Antirrhinum majus., Arch Biochem. Biophys., 2000, 382,145-151. 

D AURIA, J. C., CHEN, F., PICHERSKY, E., Characterization of an acyltransferase capable of synthesizing benzylbenzoate and other volatile esters in flowers and damaged leaves of Clarkia breweri., Plant Physiol., 2002,130,466-476. 

Other, more volatile esters, have pleasant, fruity smells and flavours. These three are components of the flavours of bananas, rum, and apples ... 

Exposure > DNEL if accidentally ingested or inhaled or zero-threshold Volatile esters of BAA ammonium sulfides [302] Not allowed as a liquid or gaseous substance or preparation in ornamental devices or in toys... 

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