Lactone, aroma substance

Among the fragrance and aroma substances a great variety of mono- and polyole-finic aliphatic alcohols, aldehydes, ketones, carboxylic acids, and their esters, as well as lactones are found 158). Of these aroma substances, (J5)-2-alkenals, ( )-2-alkenoic acids, ( )-2-alkenoic esters as well as (JS)-2-alken-l-ols are predestinated for the synthesis via the Wittig reaction because of the ( )-stereoselectivity of the olefination using resonance-stabilized ylides. 

Several lactic acid derivatives were used by Gessner et al. for the determination of the enantiomeric purity of flavor substances such as chiral alcohols from natural sources. Diastereomeric 0-acetyl-, propionyl-, and hexanoyllactic acid esters of the chiral alcohols were separated by GLC (155). A report from the same laboratories described characterization of several chiral aroma substances that are S-lactones. The lactones were hydrolyzed to the corresponding hydroxy acids, and the acid moiety was esterified to the isopropyl ester. The remaining hydroxyl group was esterified with (R)-2-phenylpropionic add chloride or [30], and the diastereomeric derivatives were separated using preparative silica gel LC. The derivatives were also separated on an analytical scale by GLC (156). 

Many microbial metabolites are volatile compounds and in terms of their sensory properties can be broken into two broad categories odorants and tastants (Table 1). Tastants include salty, sour, sweet, and bitter compounds such as amino acids, peptides, and sugars. Primary odorants typically are quite volatile and include carbonyl compounds, esters, and terpenes. There is considerable overlap between the two categories lactones, for example, have both taste and odor properties. In keeping with the theme of this symposium, volatile aroma substances will be the primary focus. 

Apple flavor The sometimes marked differences between aromas of individual varieties of apples are mainly due to quantitative variations in the composition of apple flavor substances. Key components are ethyl (+)-2-methylbutanoate and other esters of 2-methylbutanoic acid, in addition to ethyl and hexyl bu-tanoates, hexyl acetate, (E)-2- and (2)-3-hexenyl acetates (see fruit esters) and j3-damascenone. ( )-2- Hexenal, ( )-2- hexen-l-ol, and hexanal (see alka-nals) play a special role in A. f. These are trace aroma substances in intact apples. When the fruit cells are destroyed, the concentration of the Cg units increase strongly due to enzymatic processes. They are the main aroma components of apple juice. Accordingly, the aromas of fresh apples and apple juice differ markedly. Apricot flavor The typical aroma is due to the combined effects of numerous components with flowery and fruity characters these include linalool, 1-ter-pinen-4-ol, a-terpineol (see p-menthenols), 2-phen-ylethanol, a- and )8- ionones, /5- damascenone, and (Z)-jasmone for the flowery part together with fruit esters and lactones, e. g., 4-octanolide, 4- and 5-deca-nolide, 4-dodecanolide (see alkanolides), hexyl acetate and hexyl butanoate for the fruity part, rounded off by benzaldehyde. 

Among the monoterpenoid lactones, derivatives of the iridane series 600) have acquired limited importance as aroma substances. Nepetalactone (143) occurs in quantities of up to 78% in American oil of catnip Nepeta cataria L.) 490), while epinepetalactone (144) is the major constituent (70%) of the essential oil of Nepeta mussini L. 490). The essential oil of this species was also found to contain neonepetalactone (146) as well as the two saturated compounds a- and 5-dihydronepetalactones (147) and (148) 490, 518) and 5,9-dehydronepetalactone (145) 528). Both dihydro compounds (147) and (148) are structurally closely related to the iri-domyrmecins from Actinidia polygama 515, 516). Lactones (143) to (150) are aroma compounds which have a strong odor and which exert an attracting effect on Felidae 518, 519). 

Numerous lactones are found in food. Some of the representatives which belong to the typical aroma substances of butter, coconut oil, and various fruits are presented in Table 5.31. 

In the AEDA of UHT milk (Table 10.38), 5-decalactone, which contributes to the aroma of butter (Table 10.40) as well as unripened and ripened cheese (cf. 10.3.5), is the predominant aroma substance. Apart from other lactones, 2-acetyl-l-pyrroline, methional, 2-acetyl-2-thio-azoline and 4,5-epoxy-2-decenal are among the identified aroma substances. 

Since the aroma of lactones is partly very pleasant, these substances are also of interest for commercial aromatization of food. In the homologous series of y- and 5-lactones, the odor threshold decreases with increasing molecular weight (Table 5.32). 

The aroma of apricots (Armeniaca vulgaris, syn. Prunus armeniaca, Rosaceae) is composed of a large number of different substances. Important components are monoterpenic hydrocarbons, alcohols and aldehydes (myrcene, hmonene, p-cymene, terpinolene, a-terpineol, geranial, geraniol and hnalool in particular) and aldehydes with green flavour, such as (Z)-hex-3-enal and acetaldehyde. Other volatile components include products of oxidation of fatty acids, such as (2 ,6Z)-nona-2,6-dienal, (Z)-octa-l,5-dien-3-one, lactones (y-hexalactone, y-octalactone, y-decalactone, y-dodecalactone, 8-decalactone and 8-dodecalactone), carboxylic acids (especially, 2-methylbutanoic and acetic acids) and degradation products of carotenoids, such as P-ionone. 

Pineapple Ananas comosus, Bromeliaceae) aroma consists of about 200 alcohols, esters, lactones, aldehydes, ketones, monoterpenes, sesquiterpenes and other volatiles. About 80% of the total volatile substances are esters. The main components in the green fruit are ethyl acetate, ethyl 3-(methylthio)propionate (8-189) with a distinctive pineapple aroma and ethyl 3-(acetoxy)hexanoate (8-190). The ripe fruit contains, as the main esters, ethyl acetate, (2J ,3i )-butane-2,3-diol diacetate (8-191) and ketone 3-hydroxy-butan-2-one. An important compound for the typical character of pineapple aroma, as in strawberry aroma, is 2,5-dimethyl-4-hydroxy-2//-furan-3-one (furaneol), present as a glycoside, and 2,5-dimethyl-4-methoxy-2H-furan-3-one. 

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