Nonvolatile lipids

Lungs also secrete nonvolatile compounds. Lipid-soluble compounds may thus be transported with the alveobronchotracheal mucus to the pharynx, where they are swallowed. They may then be excreted or reabsorbed. Particles are also removed by this mucociliary escalator. 

Plant resins are lipid-soluble mixtures of volatile and nonvolatile terpenoid and/or phenolic secondary compounds that are usually secreted in specialized structures located either internally or on the surface of the plant. Although terpenoid resins constitute the majority of the resins produced and used, some other important resins are phenolic. Phenolic resin components, which occur on the surfaces of plant organs, have been used particularly in medicines [86]. 

Although El MS is an efficient way to provide structural information on several molecular constituents of various lipid substances it only provides partial information and it is particularly not suitable for the study of the low volatile components. High molecular weight and nonvolatile compounds are particularly difficult to analyse in this way and it may therefore be interesting to explore the possibilities of other ionisation modes such as electrospray for an accurate structural study of high molecular constituents such as monoester and diester species of beeswax (Gamier et al., 2002) and TAGs of animal fats... 

Marine algae transform arsenate into nonvolatile methylated arsenic compounds such as methanearsonic and dimethylarsinic acids (Tamaki and Frankenberger 1992). Freshwater algae and macrophytes, like marine algae, synthesize lipid-soluble arsenic compounds and do not produce volatile methylarsines. Terrestrial plants preferentially accumulate arsenate over arsenite by a factor of about 4. Phosphate inhibits arsenate uptake by plants, but not the reverse. The mode of toxicity of arsenate in plants is to partially block protein synthesis and interfere with protein phosphorylation — a process that is prevented by phosphate (Tamaki and Frankenberger 1992). 

Describes a simple and sensitive spectrophotometric method to estimate the content of total carbonyl compounds in rancid fats and foods by trapping them with 2,4-DNPH the technique determines total carbonyls, including those that are nonvolatile, decreasing the ability of the assay to correlate well with sensory data. Although gas chromatographic techniques are better suited for determining volatile carbonyl compounds from lipid oxidation, this is still the classical colorimetric assay. 

During AEDA, interactions between the odorants are not taken into consideration, since every odorant is evaluated individually. Therefore, it may be possible that odorants are recognized which are possibly masked in the food flavor by more potent odorants. Furthermore, the odor activity values only partially reflect the situation in the food, since OAVs are mostly calculated on the basis of odor thresholds of single odorants in pure solvents. However, in the food system, the threshold values may be influenced by nonvolatile components such as lipids, sugars or proteins. The following examples will indicate that systematic sensory model studies are important further steps in evaluating the contribution of single odorants to the overall food aroma. 

The red-sided garter snake pheromone components were isolated by hexane extraction of the skin lipids of sacrificed snakes. Female snakes yielded more total lipid than males (38.4 versus 8.4mg snake-1)80 Initial fractionation on an activity III alumina column gave a fraction (eluted with 98 2, hexanes ethyl ether) that was attractive to courting males. NMR and infrared (IR) spectra of this fraction were suggestive of the presence of methyl ketones, straight chain alkyl lipid subunits, and Z-alkenes. GC—MS analysis, including extensive consideration of the fragmentation of the electron impact MS data, led to the identification of a family of relatively nonvolatile (C29—C37) lipid methyl ketones. Specifically, the individual components of a mixture of saturated and monounsaturated methyl ketones 18—30 were identified. 

The primary oxidation products (hydroperoxides) are unstable and susceptible to decomposistion. A complex mixture of volatile, nonvolatile, and polymeric secondary oxidation products is formed through decomposition reactions, providing various indices of lipid oxidation (5). Secondary oxidation products include aldehydes, ketones, alcohols, hydrocarbons, volatile organic acids, and epoxy compounds, among others. Methods for assessing lipid oxidation based on their formation are discussed in this section. 

Monohydroperoxides are the primary products of lipid oxidation. A variety of hydroperoxides with positional and geometrical isomers are formed depending on the position and number of double bonds of the unsaturated fatty acids and the oxidation mechanism. A number of reviews have been published on the composition of isomeric hydroperoxides formed from oxidation of oleate, linoleate, and linolenate (286, 287-291). The hydroperoxides formed are odorless, but they are relatively unstable and are the precursors of a variety of volatile and nonvolatile scission products that are important to the oxidized flavor. 

Vesely and Jakes (13) pointed out that the definition for lipides adopted in 1923 was not sufficiently precise. It included, among lipides, the fats formed of mixtures of esters and nonlipidic substances (free fatty acids, steroids, carotenoids, hydrocarbons) on the other hand, certain essential oils formed mainly of esters might be considered lipides. Vesely and Jakes advocated a more precise and concise definition for lipides natural esters nonvolatile with steam and possessing no aromatic ring in their molecule. ... 

Standard Method 5520D TOG Water and wastewater Suitable for biological lipids and mineral hydrocarbons. Method D is the method of choice when relatively polar, heavy petroleum fractions are present, or when the levels of nonvolatile greases may challenge the solubility of the solvent APHA 1992 0 m H 33 O r m c... 

Another instrument called the transport detector, used for detection of lipids, proteins or carbohydrates, requires the transport of the column eluent by a moving wire disc, chain or helix. The solvent is evaporated in a furnace and the nonvolatile sample passes into a flame ionization detector (FID) which is detailed later under gas chromatography (GC) wherein FID counts amongst the major detectors. 

Senter, S.D., Payne, J.A., Miller, G., and Anagnostakis, S.L., Comparison of total lipids, fatty acids, sugars and nonvolatile organoleptic acids in nuts from four Castanea species, J. Sci. Food Agric., 65, 223-227, 1994. 

---