Passion fruits esters

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... 

Later, the chemical characterisation of the volatiles from yellow passion fruit essence and from the juice of the fruit was done by GC-MS and GC-olfactom-etry (GC-O) [27]. Esters were the components found in the largest concentrations in passion fruit juice and essence extracted with methylene chloride. Analysis by GC-O yielded a total of 66 components which appeared to contribute to the aroma of passion fruit juice and its aqueous essence. Forty-eight compounds were identified in the pulp of Brazilian yellow passion fruits (Passiflora edulis f. flavicarpa) [48]. The predominant volatile compounds belonged to the classes of esters (59%), aldehydes (15%), ketones (11%), and alcohols (6%). 

Methods for the capillary gas chromatographic separation of optical isomers of chiral compounds after formation of diastereoisomeric derivatives were developed. Analytical aspects of the GC-separation of diastereoisomeric esters and urethanes derived from chiral secondary alcohols, 2-, 3-, 4- and 5-hydroxy-acid esters, and the corresponding jf- and -lactones were investigated. The methods were used to follow the formation of optically active compounds during microbiological processes, such as reduction of keto-precursors and asymmetric hydrolysis of racemic acetates on a micro-scale. The enantiomeric composition of chiral aroma constituents in tropical fruits, such as passion fruit, mango and pineapple, was determined and possible pathways for their biosynthesis were formulated. 

Odd-numbered secondary alcohols (pentanol-2, hepta-nol-2, nonanol-2) are contained as aroma components in yellow (Passiflora edulis f. flavicarpa) and purple (Pas-siflora edulis simsl passion fruits the corresponding esters however are typical constituents only of the purple variety (2 3). The capillary GC investigation of the enantiomeric composition of these chiral components revealed interesting aspects of their biogenesis. 

Figure 6. Capillary GC-separation of R-(+)-derivatives of secondary alcohols and their esters, isolated by preparative GC from yellow and purple passion fruits (DB 210, 30 m/0.33 mm i.d., 140 °C, pentanol-2 OV 101, 50 m/0.33 mm i.d., 170 °C, heptanol-2).

Hydroxyacid esters are contained in several subtropical fruits like pineapple (26), passion fruit (27) and mango (2 ). 3-Hydroxyacid derivatives are formed as intermediates during de novo synthesis and P -oxidation of fatty acids, but the two pathways lead to opposite enantiomers. S-(+)-3-Hydroxyacyl-CoA-esters result from stereospecific hydration of 2,3-trans-enoyl-CoA during P -oxidation R-(-)-3-hydroxyacid derivatives are formed by reduction of 3-ketoacyl-S-ACP in the course of fatty biosynthesis. Both pathways may be operative in the production of chiral 3-hydroxyacids and 3-hydroxyacid esters in tropical fruits. 

Ethyl 3-hydroxybutanoate, isolated from yellow passion fruit, mainly consisted of the (S)-enantiomer (82 %), comparable to the product, obtained by yeast reduction of the corresponding 3-ketoacid ester (see above). In contrast, ethyl 3-hydroxybutanoate in purple passion fruit and mango mainly consisted of the (R)-enantiomer (69 % and 78 %). 

As shown in Figure 7 ethyl 3-hydroxyhexanoate, isolated from purple passion fruit possessed the (R)-configuration, comparable to the hydroxyacid ester obtained by the reduction with baker s yeast. In contrary to that methyl 3-hydroxyhexanoate, which was isolated from aroma extracts of pineapple, consisted of the (S)-enantiomer (91 %). ... 

It seems that the biogenesis of 3-acetoxyacidesters in pineapple is an enantio-selective process, comparable to the formation of esters of secondary alcohols in passion fruits. As the enzymic hydrolysis of ethyl 3-acetoxyhexanoate by Candida utilis leads to the (S)-configurated hydroxycompound (see Figure 4), only (S)-3-hydroxyacid esters are esterified to the corresponding 3-aceto-xycompounds in pineapple. 

Opposite enantiomers of 3-hydroxyacid esters of different chain lengths in fruits, such as yellow passion fruit (16) and the influence of the structures of oxoprecursors on the optical purities of 3-hydroxyacid derivatives in incubation experiments with pineapple indicate a competition of oxidoreductases in plant systems comparable to baker s yeast. 

Capillary gas chromatographic investigation of diastereoisomeric derivatives revealed that in some fruits, such as passion fruits (9) and blackberries (17), secondary alcohols and their esters are contained in almost optically pure form. On the other hand corn (Zea mays) contains aliphatic secondary alcohols as mixtures of enantiomers the ratios depend upon the chain lengths of the alcohols. Heptan-2-ol is present mainly as (R)-enantiomer with increasing chain length the proportion of (S)-enantiomer increases. A similar distribution has been determined in coconut (Figure 4). 

Figure IV. Capillary GC-separation of (R)-(+)-MTPA-derivatives of secondary alcohols and their esters, isolated by preparative GC from yellow and purple passion fruits.

Figure V. Possible pathway for the biosynthesis of secondary alcohols, their esters, and other typical constituents of passion fruit. Enzyme (El) is operative in yellow passion fruit. The antipodal reduction catalyzed by enzyme (E2) and the following esterification take place only in the purple variety.

The enantiomeric composition of 3-hydroxyacid esters in passion fruit, mango and pineapple have been investigated. Figure VII presents the separation of (R)- and (S)-3-hydroxybutanoates. The compounds in yellow passion fruit were mainly of the (S)-(+)-configuration as predicted for intermediates of B-oxidation. In the purple variety, and in mango, the (R)-(-)-enantiomers predominate. These compounds may be found as an offshoot of de novo lipid synthesis or by hydration of (Z)-2-enoyl-CoA leading to (R)-(-)-3-hydroxyacyl-CoA (1 2) ... 

Mercaptohexanol and the corresponding esters especially contribute to the pleasant flavor of passion fruit. 

Figure X. Possible pathway for the biosynthesis of (Z)-3-hexanoic acid esters, (Z)-3-hexanol, (Z)-3-hexenyl esters, 3-hydroxyhexanoic acid esters, and sulfur-containing components in passion fruit.

Passion fruit Red Rf. (Passiflora edulis) . The flowery-fruity flavor is due in particular to (Z)-3-hexenyl esters, (Z)-3-octenyl acetate, citronellyl and geranyl acetate. Yellow P.f. (P. edulis flavicarpa). 2-Methy 1-4-propyl-1,3-oxathiane, 3-mercapto-l-hexanol (CjHuOS, Mr 134.24, CAS [51755-83-0]) and the corresponding esters are mainly responsible for the exotic-fruity flavor. In both sorts about 30 Cu-noriso-prenoids, including fl ionone, )3- damascenone and edulane (2,5,5,8a-tetramethyl-l-benzopyran) make major contributions to the aroma. 

Et ester [69925-33-3]. Aroma component of purple passion fruit Passiflora edulis. Bp7.io 90-95°. 

Hydroxybenzoic and vanillic acids are also present in numerous fruits and vegetables [1], and the native forms are frequently simple combinations with glucose (Table 1). Other derivatives have been detected in certain fruits [1,2] the methyl ester of />-hydroxybenzoic acid in passion fruit, 3,4-dihydrox-ybenzoic aldehyde in banana, a phenylpropene benzoic acid derivative in fruits of Jamaican Piper species, and benzoyl esters and other derivatives in the fruits of Aniba riparia. Different new glycosides of HBA showing radical-scavenging activity [e.g., a new guaiacylglycerol-vanillic acid ether (Fig. 1)] have been identified in the fruits of Boreava orientalis [20]. 

Pinheiro, E. R Silva, I. M. D. A Gonzaga, L. V Amante, E. R. Teofilo, R. F Ferreira, M. M. C. Optimization of extraction of high ester pectin from passion fruit peel (Passiflora edulis flavicarpa) with citric acid by using response surface methodology. Bioresource Technology, v. 99, p. 5561-5566, 2008. 

An important sulfide is methional (8-37). Methional in beer and wine is formed by the activity of microorganisms. It is partly reduced to the corresponding alcohol methionol (8-13) and reaction with acetyl-CoA yields 3-methylthiopropyl acetate (8-129), which is an important component of various fermented foods. Another ester of acetic acid 3-(methylthio)hexyl acetate is a component that posseses attractive tropical fruity notes on dilution. The less odoriferous (-)-(J )-enantiomer (8-130) is reminiscent of passion fruit, while the (-l-)-(S)-form has a more herbaceous odour. The odour thresholds of these thiols in air are 0.10 ng/1 and 0.03 ng/1, respectively. Both isomers have been found in passion fruit (Passiflora edulis, Passifloraceae), guava Psidium guajava, Myrtaceae) and aromatic white wines. Methyl-3-(methylthio)propionate, or pineapple mercaptan (8-131), has a flavour reminiscent of pineapple. S-Methylthiohexanoate (8-132) is a component of the durian fruit smell. Condensation of methional with ethanol yields (Z)-2-(methylthio)methylbut-2-enal also known as 2-ethylidenemethional (8-133), which is an important component of potato chips aroma. It also occurs in... 

Significant aliphatic sulfur compounds are methional, 3-methyl-but-2-ene-1-thiol, 3-mercapto-3-methylbutan-l-ol (8-124), its ester 3-mercapto-3-methylbutyl formate, methanethiol and dimethyltrisulfide. 3-Mercapto-3-methyl-l-ol also occurs in passion fruit and blackcurrant, and as a putative cat pheromone in cat urine, where it is formed as a degradation product of amino acid L-felinine (see Section 2.2.1.2.2). Of more than 70 known pyrazines, the most important compounds in roasted coffee are isopropylpyrazine, 2-isobutyl-3-methoxypyrazine, 2-ethyl-3,5-dimethylpyrazine, 2,3-diethyl-5-methylpyrazine, 2,6-dimethyl-3-vinylpyrazine and 2-ethyl-6-methyl-3-vinylpyrazine. Pyridine and its alkyl derivatives and bicyclic pyridines have a negative impact on the quality of coffee aroma. Important aromatic... 

The tropical category is one of the most important areas for new discoveries of key impact flavor compounds. Analyses of passion fruit and durian flavors have produced identifications of many potent sulfur aroma compounds (18). Among these is fropathiane, 2-methyl-4-propyl-l,3-oxathiane, which has an odor threshold of 3 ppb (15). For pineapple, 2-propenyl hexanoate (allyl caproate) exhibits a typical pineapple character (11) however, Furaneol, ethyl 3-methyl-thiopropionate, and ethyl-2-methylbutyrate are important supporting character impact compounds (31). The latter ester contributes the background apple note to pineapple flavor. Another character impact compound, allyl 3-cyclohexyl-... 

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