Pineapple volatiles

The earliest investigations concerning pineapple volatiles date from 1945 [23, 24]. The great majority of pineapple components are contributed by ethyl and... 

Mixtures of enantiomers rather than optically pure compounds can be rationalized by different assumptions (a) one enzyme with low enan-tioselectivity catalyzes the biogenetical process, (b) at least two enzymes with different enantioselectivities compete in the reaction, and (c) different pathways eventually leading to the same final products, however with opposite configurations, are involved. By addition of chemically synthesized precursors we aimed to trace some of the biogenetical routes involved in the biogenesis of chiral pineapple volatiles. 

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). 

Pineapple, one of the most popular tropical fruits in the world, has been cultivated in South America since the fifteenth century [61]. It has been very popular throughout the world for many years [16]. Native to Central America and South America, pineapples grow in several tropical countries, such as Hawaii, India, Malaysia, the Philippines, and Thailand [12]. Owing to its attractive sweet flavour, pineapple is widely consumed as fresh fruit, processed juice, canned fruit, and as an ingredient in exotic foods. The volatile constituents of pineapple have been studied for over 60 years by many researchers. More than 280 compounds have been found among volatiles of pineapples so far [60]. 

The sulfur components ethyl S-(+)-2-methylbutanoate and dimethyl trisulfide (with 0.006 and 0.01 pg/L odour thresholds in water, respectively) were reported as impact-flavour compounds in fresh Hawaiian pineapple essence prepared by solvent extraction. The major volatile components were methyl and ethyl esters [59]. 

The volatile compounds of juices made from freshly cut pineapple fruits from different cultivars from Costa Rica, Ghana, Honduras, Cote d Ivoire, the Philippines, Reunion, South Africa, and Thailand were studied in comparison to that of commercial water phases/recovery aromas, juice concentrates as well as commercially available juices [12]. The qualitative pineapple fruit flavour profile showed several methyl esters, some characteristic sulfur-containing esters, and various hydroxy esters were responsible for the typical pineapple flavour profile. 

Ethyl acrylate may be released into the environment in escape or stack emissions or in wastewater during its production and use. It is also a volatile component of pineapple and Beaufort cheese (a type manufactured in a small area of the French Alps). It has been detected at low levels in wastewater samples (United States National Library of Medicine, 1997). 

The desired orange flavor is the result of volatile compounds in specific proportions (Shaw, 1991). There are six major contributors to orange flavor acetaldehyde, citral, ethyl bu-tanoate, d-limonene, nonanal, octanal, and a-pinene with two major types of essence oils, early-mid and Valencia (Shaw, 1991). Early-mid oranges include Hamlin and Pineapple. 

Capillary gas chromatographic determination of optical purities, investigation of the conversion of potential precursors, and characterization of enzymes catalyzing these reactions were applied to study the biogenesis of chiral volatiles in plants and microorganisms. Major pineapple constituents are present as mixtures of enantiomers. Reductions, chain elongation, and hydration were shown to be involved in the biosynthesis of hydroxy acid esters and lactones. Reduction of methyl ketones and subsequent enantioselective metabolization by Penicillium citrinum were studied as model reactions to rationalize ratios of enantiomers of secondary alcohols in natural systems. The formation of optically pure enantiomers of aliphatic secondary alcohols and hydroxy acid esters using oxidoreductases from baker s yeast was demonstrated. 

Volatile Constituents of Pineapple Ananas Comosus [L.] Merr.)... 

The volatiles of fresh pineapple (Ananas comosus [L] Merr.) crown, pulp and intact fmit were studied by capillary gas chromatography and capillary gas chromatography-mass spectrometry. The fnjit was sampled using dynamic headspace sampling and vacuum steam distillation-extraction. Analyses showed that the crown contains Cg aldehydes and alcohols while the pulp and intact fruit are characterized by a diverse assortment of esters, h rocarbons, alcohols and carbonyl compounds. Odor unit values, calculated from odor threshold and concentration data, indicate that the following compounds are important contributors to fresh pineapple aroma 2,5-dimethyl-4-hydroxy-3(2H)-furanone, methyl 2-methybutanoate, ethyl 2-methylbutanoate, ethyl acetate, ethyl hexanoate, ethyl butanoate, ethyl 2-methylpropanoate, methyl hexanoate and methyl butanoate. 

Though pineapple flavor has been extensively studied relatively little work has been done on the odor properties and significance of the various constituents ( , ) This study investigates the odor contribution of various constituents. The volatiles from three parts of fresh pineapple, the crown, pulp and intact fmit were examined. 

Two intact pineapples (without crowns, total weight, 3.2 kg) were placed into a 9L glass container. The volatiles were collected, eluted and concentrated in the same manner as described above. 

Table I lists the compounds identified in a headspace sample of pineapple crowns. The sample was characterized by low levels of very few volatiles. The Ce compounds, hexanal, (Z)-3-hexenal, (E)-2-hexenal and (Z)-3-hexenol were probably produced enzymatically in response to tissue damage from cutting (12). Hydrocarbons identified include styrene, and the monoterpenes, a- and p-pinene.

Figure 2. Capillary gas chromatogram of blended pineapple pulp volatiles obtained by dynamic headspace sampling. Temperature programmed from SOX (4 min isothermal) to 180X at 2X/min on a 60m X 0.32 mm i.d. DB-WAX column. The peak numbers correspond to the numbers in Table II.

Table II. Volatile Constituents of Pineapple - Blended Pulp (Headspace)...

The vacuum SDE method confirmed the presence of nearly all of the constituents identified using dynamic headspace sampling and revealed many additional compounds. The method was more effective in extracting the less volatile const rtuents such as long chain esters. In contrast to the previous runs this sample was chromatographed on a nonpolar DB-1 column. The constituents identified in the pulp sample prepared by vacuum SDE are listed in Table VI. The %area values should be considered as only approximate since known pineapple constituents such as ethyl acetate, methyl propanoate, methyl 2-methylpropanoate, ethyl propanoate, ethanol, propyl acetate, and ethyl 2-methylpropanoate co-elute with the solvent peaks and hence could not be included in the quantitation. 

C. Preston, E. Richhng, S. Elss, M. Appel, F. Heckel, A. Hartheb, P. Schreier (2003) On-line gas chromatography combustion/pyrolysis isotope ratio mass spectrometry (HRGC-C/P-IRMS) of pineapple Ananas comosus L. Merr.) volatiles. J. Agric. Food Chem. 51, 8027-8031... 

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