Volatile lipids

It is often too expensive to have or maintain an inhouse descriptive sensory panel. Therefore, other ways of measuring flavor need to be developed. Off-flavor in many foods have been measured by using gas chromatography to assess the level of lipid volatiles associated with off-flavor development Chapters 5, 6, 9) such as hexanal or by direct chemical determination of thiobarbituric acid reactive substances Chapters 5, 6) as a marker of the degree of lipid peroxidation. A new method being tested for use in the assessment of food qu ity is impedance technology. This method is showing promise for use in the seafood industry Chapter 20),... 

Homstein and Crowe 18) and others (79-27) suggested that, while the fat portion of muscle foods from different species contributes to the unique flavor that characterizes the meat from these species, the lean portion of meat contributes to the basic meaty flavor thought to be identical in beef, pork, and lamb. The major differences in flavor between pork and lamb result from differences in a number of short chain unsaturated fatty acids that are not present in beef. Even though more than 600 volatile compounds have been identified from cooked beef, not one single compound has been identified to date that can be attributed to the aroma of "cooked beef." Therefore, a thorough understanding of the effect of storage on beef flavor and on lipid volatile production would be helpful to maintain or expand that portion of the beef market. 

GC methods are capable of determining volatile oxidation products that are either directly responsible for or serve as markers of flavor development in oxidized lipids. GC analyses for volatile compounds not only correlate with flavor scores by sensory analyses, but also provide sensitive methods to detect low levels of oxidation in various oils and food lipids. Volatile compounds... 

Bromothymol blue (6.0...7.6) acid lipids, cholesterol glucuronides and gangliosides [241] aryloxybutanolamine derivatives [242] norfenfluramine derivatives [243] ethylamphetamines [244] in volatile mineral oil hydrocarbons [245] phospholipids [91]... 

A glyceryl 2-aminoethylphosphonolipid has been isolated from Tetrahymenapyriformis and (45) has been detected by g.l.c.-mass spectrometry in both the lipid and proteinaceous fractions of human brain. The zwitterionic (45) was converted into volatile (46) by acetylation and methylation. Phosphonolipids derived from A-methyl-(45) have been synthesised by acetylation of A-methyl-(45) and subsequent conversion to the phosphorochloridate for the phosphorylation step. °... 

Lipid hydroperoxides are either formed in an autocatalytic process initiated by hydroxyl radicals or they are formed photochemically. Lipid hydroperoxides, known as the primary lipid oxidation products, are tasteless and odourless, but may be cleaved into the so-called secondary lipid oxidation products by heat or by metal ion catalysis. This transformation of hydroperoxides to secondary lipid oxidation products can thus be seen during chill storage of pork (Nielsen et al, 1997). The secondary lipid oxidation products, like hexanal from linoleic acid, are volatile and provide precooked meats, dried milk products and used frying oil with characteristic off-flavours (Shahidi and Pegg, 1994). They may further react with proteins forming fluorescent protein derivatives derived from initially formed Schiff bases (Tappel, 1956). 

A review by Bailey and Swain ( ) cited several references which indicated nitrite was responsible for cured meat flavor. These same authors presented chromatograms of volatiles from cured and uncured hams and while the chromatograms were similar, some quantitative differences led to the conclusion that the major difference due to nitrite was its reactivity to retard lipid oxidation. Greene and Price ( ) suggested, however, that sodium chloride was the major factor responsible for cured meat flavor rather than sodium nitrite or an absence of lipid oxidation. It has been concluded from other recent work (2) that nitrite was necessary to produce a typical ham aroma and flavor as well as to retard the development of off-odors and flavors during storage of cooked cured meat. 

As with urine, saliva (spumm) is easy to collect. The levels of protein and lipids in saliva or spumm are low (compared to blood samples). These matrices are viscous, which is why extraction efficiency of xenobioties amoimts to only 5 to 9%. By acidifying the samples, extraction efficiencies are improved as the samples are clarified, and proteinaceous material and cellular debris are precipitated and removed. Some xenobioties and their metabohtes are expressed in hair. Hair is an ideal matrix for extraction of analytes to nonpolar phases, especially when the parent xenobioties are extensively metabolized and often nondetectable in other tissues (parent molecules of xenobioties are usually less polar than metabolites). Hair is a popular target for forensic purposes and to monitor drug compliance and abuse. Human milk may be an indicator of exposure of a newborn to compounds to which the mother has been previously exposed. The main components of human milk are water (88%), proteins (3%), lipids (3%), and carbohydrates in the form of lactose (6%). At present, increasing attention is devoted to the determination of xenobioties in breath. This matrix, however, contains only volatile substances, whose analysis is not related to PLC applications. 

Preliminary purification of a starting band contaminated with plant oil should be performed by predevelopment with a nonpolar solvent such as benzene or n-heptane, delivered from the eluent container. Weakly retained ballast substances (e.g., lipids) move with the solvent to the edge of the adsorbent layer, covering the glass plate where the volatile solvent evaporates. The contaminants can then be removed (scraped out with the adsorbent) from the layer or adsorbed on the strip of blotting paper placed on the upper edge of the layer. 

The basic technology for the preparation of sample material is similar in all TLC preparations, irrespective of the origin of the hpid and specific preparation method for a variety of biological samples [43]. The most important factor is the solubihty of the sample. The lipid sample must be completely soluble in the dissolving solvent prior to the application and must be free from water. Either toluene or chloroform is commonly used as the solvent to dissolve hpid materials. The dissolving solvent should be nonpolar in namre and volatile at such a concentration that the hpid components in the sample are completely adsorbed throughout the entire thickness of the layer as quickly as possible. Although sample sizes as small as 1 to 10 pi can... 

Dillard, C.J. and Tappel, A.L. (1979). Volatile hydrocarbon and carbonyl products of lipid peroxidation a comparison of pentane, ethane, hexanal and acetone as in vivo indices. Lipids 14, 989-995. 

The lipase-catalyzed fatty acid ester hydrolysis and the lipoxygenation of free polyunsaturated fatty acids are involved in the same lipid degradation pathway. They are respectively the first and second reaction in the lipoxygenase pathway (Fig. 3) [87-91]. The pathway produces volatile products of considerable importance in food technology including Cg[92, 93] or Cg- 94—96 aldehydes and alcohols from polyunsaturated fatty... 

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). 

TLC spots with marker reveal the presence of free fatty acids (FFA), diglyceride (DG), monoglyceride (MG) but negligible amount of TG. GCMS of fatty acid— methyl esters (FAME) from lion mane presented evidence for fatty acids ranging from C9-C24 (Figs. 5.3- 5.6). Low volatility molecules like nonanedioic acid (Fig. 5.3), tridecanoic acid (Fig. 5.4), 12-methyl tridecanoic acid were also present in lion hair lipids. In addition fatty acids such as myristic, pentadecanoic, palmitic, heptanoic, stearic and octadecenoic acids (Fig. 5.5) have also been detected. Erucic... 

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