Carbonyls volatile aroma

In addition to the enzymically-derived volatile aroma compounds (Table I), low levels of autoxidatively-derived carbonyls can also be detected in harvested fish held a day on ice, and these volatiles are listed in Table II. The oxidatively-derived carbonyls modify the fresh plant-like aromas of fresh fish by providing oxidized-oil-like, staling fish-type odor notes (3-5, 9). The formation of hexanal in freshly harvested fish appears to be enzymic because the concentration of this compound can be diminished by lipoxygenase inhibitors (25). However, when fresh fish are stored on ice or are held under frozen storage, hexanal concentrations also increase because of autoxidative processes (40). 

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. 

Preparation and storage of products from both oilseeds is often inhibited by rancidity and bitter aroma defects caused mostly by volatile aroma active carbonyl compounds, e. g., (Z)-3-hexenal, (Z)-l,5-octadien-3-one and 3-methyl-2,4-nonan-dione. The rancidity-causing compounds are formed through peroxidation of linolenic acid, accelerated by the enzyme lipoxygenase and/or by hem(in) proteins (cf. 3.T.2.2). Furan fatty acids are the precursors in the case of the dione (cf. 14.3.2.2.5). Lipid peroxidation is also involved in the formation of another very potent odorant, 2-pentylpyridine, which produces grassy aroma defects in soybean products. Defatted soybean protein isolates contained 60-510 pg/kg of this compound, which with an odor threshold... 

Flavor is one of the major characteristics that restricts the use of legume flours and proteins in foods. Processing of soybeans, peas and other legumes often results in a wide variety of volatile compounds that contribute flavor notes, such as grassy, beany and rancid flavors. Many of the objectionable flavors come from oxidative deterioration of the unsaturated lipids. The lipoxygenase-catalyzed conversion of unsaturated fatty acids to hydroperoxides, followed by their degradation to volatile and non-volatile compounds, has been identified as one of the important sources of flavor and aroma components of fruits and vegetables. An enzyme-active system, such as raw pea flour, may have most of the necessary enzymes to produce short chain carbonyl compounds. 

An extensive list of volatile compounds in apples and other fruits was included in a review by Nursten (222). White (223) reported that the principal components of the aroma of apples were alcohols (92% ) methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-methyl-l-propa-nol, 2-methyl-l-butanol, and 1-hexanol. The other constituents included 6% carbonyl compounds and 2% esters. Later, MacGregor et al. (224) tentatively identified 30 volatile components of McIntosh apple juice including four aldehydes, one ketone, 11 alcohols, 10 esters, and four fatty acids. The major organic volatiles in several different extractants of Delicious apple essence were identified and quantitatively estimated by Schultz et al. (225). They reported from sensory tests that low molecular weight alcohols contributed little to apple aroma. Flath et al. (226) identified... 

Some reviews (41, 52-54) are available. The positive aspects are found in the production of desirable flavors and aromas. Fujimaki and Kurata ( 55) listed aldehydes and pyrazines, volatile compounds produced by heating amino acids with carbonyl compounds, isovaleraldehyde produced by reaction of leucine with carbonyl compounds (aldehydes,... 

Lipid decomposition volatiles. Reactions of sugar and amino acids give rise to odor profiles that are, at best, common to all cooked or roasted meats. The water soluble materials extracted from chicken, pork, or beef give reasonably similar meat flavor. To develop a species specific aroma one needs to study the lipid fraction and the volatiles produced from those lipids. The work of Hornstein and Crowe (10) reported that the free fatty acids and carbonyls generated by heating will establish the specific species flavor profiles. 

From our aroma research on boiled small shrimps, almost one hundred volatile components were identified. Among them, more than forty components were determined as sulfur- and/or nitrogen-containing heterocyclic substances, together with various kinds of volatiles that are well known to be thermally generated such as hydrocarbons, carbonyl compounds, alcohols and phenols. The shrimp... 

Other investigators (7-9) have identified a large number of carbonyls from heated fat. The remaining meat aroma components derived by heating lipids are esters, lactones, alkan-2-ones (methyl ketones), benzenoids and other alkylfurans. Several investigators have analyzed volatile compounds formed during thermal degradation of fatty acids (10-12). 

Aroma compounds in cured vanilla beans from different countries, e.g. Madagascar, Tonga, Costa Rica, Java, Indonesia and Mexico, have been documented. Over 100 volatile compounds have been detected, including aromatic carbonyls, aromatic alcohols, aromatic acids, aromatic esters, phenols and phenol ethers, aliphatic alcohols, carbonyls, acids, esters and lactones, of which the aldehyde vanillin is the most abundant. The level of the aldehydes, e.g. vanillin and p-hydroxy-benzaldehyde and their respective acids (vanillic acid and p-hydroxybenzoic acid), in cured vanilla beans is used as an indicator of cured vanilla bean quality for commercial purposes (Klimes and Lamparsky, 1976 Adedeji et al., 1993 Ranadive, 1994). 

To conclude, it is worth reiterating that the only orchid used as a spice, the vanilla pod, has been recognized for its culinary and medicinal uses since the time of the Aztecs. Vanilla is the world s third most expensive spice, from which is obtained the popular commercial flavouring agent, vanillin. The characteristic aroma of vanilla is obtained only after a time-consuming and labour-intensive curing process. The main aroma compound in vanilla is vanillin over 100 volatile compounds have been detected, including aromatic carbonyls, aromatic... 

In our opinion, the predominant contribution to flavor seems to come from sulfurous and carbonyl-containing volatiles. While many of the sulfur-containing volatiles are known to have meaty aromas, volatile carbonyl compounds generally are formed by lipid autoxidation/degradation and do not possess meaty flavor notes. However, it has been indicated that the carbonyl compounds are responsible for the "chickeny" aroma of cooked chicken (17). Thus, lipid autoxldatlon appears to yield the character impact compounds for chicken (18). 

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. 

Flavors and aromas commonly associated with seafoods have been intensively investigated in the past forty years ( l-7), but the chemical basis of these flavors has proven elusive and difficult to establish. Oxidized fish oils can be described as painty, rancid or cod-liver-oil like (j ), and certain volatile carbonyls arising from the autoxidation of polyunsaturated fatty acids have emerged as the principal contributors to this type of fish-like aroma ( 3, 5, 9-10). Since oxidized butterfat (9, 11-12) and oxidized soybean and linseed oils (13) also can develop similar painty, fish-like aromas, confusion has arisen over the compounds and processes that lead to fish-like aromas. Some have believed that the aromas of fish simply result from the random autoxidation of the polyunsaturated fatty acids of fish lipids (14-17). This view has often been retained because no single compound appears to exhibit an unmistakable fish aroma. Still, evidence has been developed which indicates that a relatively complex mixture of autoxidatively-derived volatiles, including the 2,4-heptadienals, the 2,4-decadienals, and the 2,4,7-decatrienals together elicit unmistakable, oxidized fish-oil aromas (3, 9, 18). Additionally, reports also suggest that contributions from (Z -4-heptenal may add characteristic notes to the cold-store flavor of certain fish, especially cod (4-5). 

Generally, the volatile carbonyls found in fish exhibit coarse, heavy aromas whereas the volatile alcohols contribute smoother qualities. Lower threshold values for the volatile carbonyls, especially l-octen-3-one (0.005 ppb 39) ... 

The relative ratios of alcohols and carbonyls for the six-, eight- and nine-carbon volatiles in fish (23-24) and oysters (26) parallel those encountered in cucumber fruits (37) and mushrooms (27, 56) if the two systems are combined. Therefore, the use of plant-based enzyme systems for the controlled generation of fresh seafood flavors and aromas has been under consideration in our laboratory as a means to overcome some of the self-inactivating problems associated with fish lipoxygenases. 

The descriptions of aromas produced in these systems are shown in Table IV. The principal compounds which contribute to the initial fish-like aromas of surimi appear to be the enzymically-derived eight-carbon carbonyls and alcohols in combination with some oxidized fishy aroma undertones that are caused by very low levels of autoxidatively-derived carbonyls, including the 2,4-heptadienals and the 2,4-decadienals (unpublished data). When geranium leaves were macerated before addition to surimi, the six-carbon volatile compounds dominated the overall aroma, and the desirable contributions associated... 

The aromas associated widi very fi esh fish are usually mild, delicate and fi esh (53,54), and generally described as green (hexanal), melon-like ((E,Z)-3,6-nonadienal), iodine-like (bromophenols). Fresh fish and seafood aromas are due to volatile carbonyls and derive fi om lipoxygenase catalyzed oxidation of polyunsaturated fatty acids. The oxidation of Eicosapentaenoic acid (C20 5) leads to C5 to C9 alcohols, aldehydes, ketones and hydrocarbons. The formation of methyl mercaptan, dimethyl sulfide and dimethyl disulfide in fi esh fish at the time of harvest has been reported by Shiomi et al. (55). Although these compounds are usually associated with fish deterioration, they contribute to the fi esh aroma ch cter at low concentrations. For instance, dimethyl sulfide is... 

---