Lipid derived volatile compounds

Lipid-derived volatile compounds play an important role in the flavor of foods. These compounds contribute to the characteristic notes of many dairy flavors, but are also responsible for many off-flavors. Parliament and McGorrin (2000) reviewed those volatile compounds important in milk, cream, butter, cultured creams and cheese. The pathways involved in the degradation of milk fat have also been reviewed by McSweeney and Sousa (2000) and compounds include FFAs, methyl ketones, lactones, esters, aldehydes, primary and secondary alcohols, hydroxyacids, hydroperoxides and ketoacids. 

Lipid-Derived Volatile Aroma and Flavor Compounds... 

Lipid-derived volatile compoimds dominate the flavor profile of pork cooked at temperatures below 100°C. The large numbers of heterocyclic compounds reported in the aroma volatiles of pork are associated with roasted meat rather than boiled meat where the temperature does not exceed 100 C (34,35). Of flie volatiles produced by lipid oxidation, aldehydes are the most significant flavor compounds (35,36). Octanal, nonanal, and 2-undecenal are oxidation products from oleic acid, and hexanal, 2-nonenal, and 2,4-decadienal are major volatile oxidation products of linoleic acid. 

The structure of the food matrix is also known to affect the release of volatile compounds having an impact on flavors and aroma. Changes in flavor result from the interactions of lipid-derived carbonyl compounds by aldolization with the amino groups of proteins. Undesirable flavors are produced when beef or chicken are fried in oxidized fats by the interaction of secondary lipid oxidation... 

Phospholipids contribute specific aroma to heated milk, meat and other cooked foods through lipid oxidation derived volatile compounds and interaction with Maillard reaction products. Most of the aroma significant volatiles from soybean lecithin are derived from lipid decomposition and Maillard reaction products including short-chain fatty acids, 2-heptanone, hexanal, and short-chain branched aldehydes formed by Strecker degradation (reactions of a-dicarbonyl compounds with amino acids). The most odor-active volatiles identified from aqueous dispersions of phosphatidylcholine and phos-phatidylethanolamine include fra 5 -4,5-epoxy-c/5-2-decenal, fran5,fran5-2,4-decadienal, hexanal, fra 5, d5, d5 -2,4,7-tridecatrienal (Table 11.9). Upon heating, these phospholipids produced cis- and franj-2-decenal and fra 5-2-undecenal. Besides fatty acid composition, other unknown factors apparently affect the formation of carbonyl compounds from heated phospholipids. 

Volatile compounds formed by anabolic or catabolic pathways include fatty acid derivatives, terpenes and phenolics. In contrast, volatile compounds formed during tissue damage are typically formed through enzymatic degradation and/ or autoxidation reactions of primary and/or secondary metabolites and includes lipids, amino acids, glucosinolates, terpenoids and phenolics. 

In Figure 3, as in Figure 2, samples isolated from oats with 7.4% and 8.3% lipid content were different with regard to chemical composition. Since the oil itself may play several roles, for example as generator of aroma compounds as well as solvent for other volatile compounds, it is of interest to follow the aroma pattern in the abovementioned samples. The amount of heterocycles decreased in most cases when the initial oat lipid content increased. Compounds such as pyrazine derivatives (methyl, 2,5-dimethyl, 2,6-dimethyl, 2-ethyl-5-methyl, trimethyl, 2,5-methyl-3-ethyl), furfural, 5-... 

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). 

However, the formation of volatile aroma compounds from the interaction of Maillard intermediates with lipid-derived compounds has received little attention. 

Volatile compounds generated by model systems of zeln, corn amylopectin and corn oil extruded at barrel temepratures of 120°C and 165°C were analyzed by GC and GC/MS. The largest quantities of lipid oxidation products were detected in systems containing all three components. In each system, the quantity of 2,4-deca-dienal was low relative to the quantities of hexanal, heptanal and benzaldehyde. Identification of the Maillard reaction products, 2-methyl-3(or 6)-pentyl-pyrazine, 2-methyl-3(or 6)-hexylpyrazine and 2,5-di-methyl-3-pentylpyrazine, suggested that lipid-derived aldehydes might be involved in the formation of substituted pyrazines. 4-Methylthiazole was identified as a major decomposition product of thiamin when corn meal containing 0.5% thiamin was extruded at a final temperature of 180°C. 

The most widely used method for quantifying FFAs is gas chromatography (GC), which has attained widespread favor due to its versatility, high sensitivity and relatively low cost. GC complexed with a flame ionization detector is used routinely to quantify FFAs, either directly or derivatized as fatty acid methyl esters (FAME). GC with mass spectroscopic detection has become the favored technique for quantification of volatile compounds derived from lipids (esters, lactones, ketones, alcohols and acids). 

Virtually all volatile aromatic and flavorsome lipid-derived compounds are analyzed using gas chromatography-mass spectrometry (GC-MS). The components of interest are isolated initially, concentrated, then injected onto a suitable capillary column and detected using a mass spectrometer. 

The oxidation products of lipids include volatile aldehydes and acids. Therefore, lipids are one of the major sources of flavors in foods. For example, much of the desirable flavors of vegetables such as tomatoes, cucumbers, mushrooms, and peas (Ho and Chen, 1994) fresh fish (Hsieh and Kinsella, 1989), fish oil (Hu and Pan, 2000) and cooked shrimp (Kuo and Pan, 1991 Kuo et al., 1994), as well as many deep-fat fried foods such as French-fried potatoes (Salinas et al., 1994) and fried chicken (Shi and Ho, 1994), are contributed by lipid oxidation. LOX-catalyzed lipid oxidation produces secondary derivatives, e.g., tetradecatrienone, which is a key compound of shrimp (Kuo and Pan, 1991). The major difference between the flavors of chicken broth and beef broth is the abundance of 2,4-decadienal and y-dodeca-lactone in chicken broth (Shi and Ho, 1994). Both compounds are well-known lipid oxidation products. A total of 193 compounds has been reported in the flavor of chicken. Forty-one of them are lipid-derived aldehydes. 

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). 

It is known that volatile compounds found in fruits are mainly derived from three biosynthetic pathways in many plants [25] The formation of the hedonically important short-chain aldehydes and alcohols, such as di-3-hexenol, takes place through the action of lipases, hydroperoxide lyases, and cleavage enzymes on lipid components, followed by the action of alcohol dehydrogenases [26]. 

The pecan tree Carya illinoinensis) is native to North America and has been commercially exploited for prodnction of pecan nuts for nearly a century, mainly in the southeastern United States. Pecan can be consumed either raw or roasted and is used extensively in confectionary, bakery, culinary, and other food product applications. Like most other tree nuts, pecan contains high amounts of lipid (55%-75%) [31-33], thus the majority of volatile compounds identified in this nut are derived via breakdown of unsaturated fatty acids. Only a few studies have been published on the volatile constituents of pecan... 

Volatile fatty acids p resent in wine may derive from the anabolism of lipids, resulting in compounds with even number of carbon atoms, by oxidative decarboxylation of a-keto acids or by the oxidation of aldehydes. Volatile fatty acids synthesised from a-keto acids are mainly propanoic add, 2-methyl-l-propanoic acid (isobutyric acid), 2-methyl-l-butanoic acid, 3-methyl-l-butanoic acid (isovaleric acid 3-methylbutyric add) and phenylacetic add. From lipid metabolism, the following fatty acids are reported butanoic add (butyric), hexanoic acid (caproic), odanoic acid (caprylic) and decanoic add (capric) (Dubois, 1994). Although fatty adds are charaderized by unpleasant notes (Table 1), only few compounds of this family attain its perception threshold. However, their flavour is essential to the aromatic equilibrium of wines (Etievant, 1991). 

The studies published in this promising area of flavor chemistry and physiology have been limited to a few volatile compounds. They need to be extended to the multitude of other volatile compounds derived from lipid oxidation. Many of these volatiles are known to have a significant impact on quality and acceptability of lipid-containing foods. The complex volatiles produced by food lipids containing n-3 polyunsaturated fatty acids reported to impart nutritional and health benefits are especially important because they develop undesirable fishy odors and flavors at extremely low levels of oxidation (Chapter 4.D Chapter 5.F Chapter ll.E). 

Not all of the potent volatile compounds are derived from lipid oxidation, including a number of lactones that come from naturally occurring hydroxy fatty acids, diacetyl and vanillin in butter oil (from melted butter). The concentrations of the mixtures of carbonyl compounds exceed the flavor threshold values for individual aldehydes, and the oxidized flavor results from a combination of volatile compounds. 

Various carbonyl volatile compounds derived by lipid oxidation in fish... 

As everyone knows, plants have been used for centuries in herbalism, homeopathy, and aromatherapy because of their medicinal qualities. The long-term use of plants has led to recent observations about their antioxidant properties (1, 2). Many scientists have observed antioxidant activities in compounds derived from the volatile constituents (3, 4) and essential oil extracts - of plants. They have reported that ingestion of these volatile chemicals can prevent lipid peroxidation, which is associated with diseases such as cancer, leukemia, and arthritis. In the present study, analysis and antioxidative tests on the volatile extract isolated from a commercial beer were performed. Why did we choose beer We chose beer because... 

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