Lipid in meat

Bitman, J. 1976. Status report on the alteration of fatty acid and sterol composition in lipids in meat, milk, and eggs. In Fat Content and Composition of Animal Products. National Academy of Sciences, Washington, D. C., pp. 200-237. 

Results for lipid content depends very much on the source material and the protocol used. Thus, oilseeds such as mustard, canola, and flax may contain 38% to 42% lipid, while starch may contain <1% total lipid. The content of lipids in meat and seafoods may vary from I % to 30%. Nutmeg contains 25% to 30% lipids. 

Fat portion of meats, particularly their phospholipid components, undergo autoxidation/degradation (2) and produce an overwhelming number of volatiles. Fats also serve as a depot of fat-soluble compounds that volatilize on heating and strongly affect flavor. Since compositional characteristics of lipids in meats, vary from one species to another, these factors may be responsible for the development of some species-specific flavor notes in cooked meats (8.9 ). Obviously presence of 4-methyloctanoic and 4-... 

Matrix solid-phase dispersion (MSPD) was developed by researchers at Louisiana State University s School of Veterinary Medicine in order to isolate, identify, and quantify veterinary drug residues in livestock (Barker and Hawley, 1992). Compared to traditional methods, MSPD reduces solvent use by 98% and turnaround time by as much as 90%. The method involves the mechanical blending of a sample matrix with bulk C-18 sorbent. The C-18 hydrophobic phase has the ability to incorporate the lipids in meat and other food products into its matrix. Mechanical shearing forces initially disrupt the sample structure and disperse the sample over the surface of the C-18 bonded silica. The process causes the sample and polymer phase to become semidry, which then allow the material to be packed into a column (see Fig. 9.4). 

Lipids in meat are not considered a main structural element, although they are important constituents of the cellular membranes. In addition, lipids in meat are relevant because they are necessary to produce the typical pleasant flavor and mouth sensation. However, excessive amounts of lipids decrease the lean usable portion without improving the quality. 

Mottram, D.S. Some observations on the role of lipids in meat flavour. In Sensory quality in foods and beverages (Eds. Williams. A.A., Atkin, R.K.), p. 394, Ellis Horwood Ltd. Chichester. 1983 Muller, W.-D. Fleischverarbeitung. In Taschenbuch fUr Lebensmittelchemiker und -technologen. Band 2 (Ed. D. Osteroth) Springer-Verlag, Berlin, 1991, pp. 387... 

Mincing, cooking and maturing expose meat products to oxidative stress for a long time so that antioxidants added for lipid protection are slowly destroyed on storage. Onion juice is a powerful antioxidant in meat products, more efficient than garlic juice. Lipid hydroperoxides are reduced to inactive hydroxyl derivatives by reaction with sulphur compounds present in those juices. 

SKIBSTED L H, MiKKELSEN A and BERTELSEN G (1998) Lipid-derived off-flavours in meat, in Shahidi F Flavour of Meat, Meat Products and Seafoods, Blackie Academic Professional, London, 217-56. 

The lipid in muscle is composed primarily of triglycerides (depot fats) and of phospholipids (membrane components), and is a constituent which varies enormously not only in amount present, but also in properties such as degree of saturation (species dependent). The ash of lean meat is comprised of various minerals such as phosphorus, potassium, sodium, magnesium, calcium, iron and zinc Carbohydrate was not noted in the proximate composition because while some may be present, it is normally there in low concentration compared to the other constituents. Glycogen is the carbohydrate occurring in greatest concentration in muscle but is normally degraded soon after the animal is sacrificed. 

The use of SPE with porous materials such as alumina, diatomaceous earth, Horisil and silica for the cleanup of fat-soluble organochlorine pesticides in fatty foods such as meat, flsh, shellfish, milk and vegetable oils has been well documented. The choice of elution solvents is critical because relatively small amounts of lipid in the final extract can cause rapid deterioration of GC capillary columns and also contaminate the gas chromatograph. A number of workers have used a porous material in tandem with Cig to effect an improved cleanup.Di Mucchio employed a multicartridge system comprising Extrelut, silica and Cig to extract organophosphorus pesticides from oils and fatty extracts. Relatively few literature applications include the pyrethroids, but Ramesh and Balasubramanian reported a simple carbon-based SPE method for the analysis of pyrethroids in vegetable oil. 

Smiddy M., Fitzgerald M., Kerry J.P., Papkovsky D.B., O Sullivan C.K., Buckley D.J., Guilbault G.G., Use of oxygen sensors to non-destructively measure the oxygen content in modified atmosphere and vacuum packed beef impact of oxygen content on lipid oxidation, Meat Science 2002 61 285-290. 

Denaturation of hemoproteins in cooked meats leads to liberation of the heme and oxidation of the porphyrin ring. Nonheme iron is less available nutritionally than heme iron and affects lipid oxidation more. In methemoglo-bin and metmyoglobin solutions heated for one hour at 78°C and 100°C the degradation of heme was about 22 to 26%, while after two hours at 120°C it increased to about 85 to 95% (Oellingrath, 1988). In meat cookery, however, such severe conditions do not apply. 

The flavor quality of food is a primary factor involved in a consumer s decision to purchase a food item. Therefore, food technologists require a thorough understanding of how flavor deteriorates if they are to prepare products that consumers will purchase repeatedly. This knowledge is particularly important in meat and meat products, since the deterioration of meat flavor is a serious and continual process (1-4) that involves both the loss of desirable flavor components 4,5) and the formation of off-flavor compounds (6-9) many of which are associated with lipid oxidation (10). 

Supercritical COj (SC-CO2) was used to reduce the lipid of meat and the cholesterol of meat and beef tallow. Lipids can be removed quantitatively from dried muscle foods by SC-CO2, but relatively high temperatures are needed. The use of SC-CO2 in conjunction with ethanol, adsorbents and multi-separators also reduced the cholesterol of beef tallow. SC-CO2 was also used to concentrate volatile flavor compounds from beef and pork fat. The volatile components in various extraction fractions were identified and quantitated. 

The most practical method for preventing WOF in meat products is to add antioxidants prepared from natural precursors such as sugars and amino adds by heating them to produce constituents that not only act as antioxidants but serve to enhance meaty flavor as well. The resulting Maillard products have been known to have antioxidant activity in lipid systems (6-8). It is assumed that the antioxidative property of the Maillard reaction is assodated with the formation of low molecular weight reductones and high molecular weight melanoidins (6, 7, 9-13). 

Liu, H. P. (1970a). Catalysts of lipid peroxidation in meats. 1. Linoleate peroxidation catalyzed by MetMb or Fe(ll)-EDTA. 7. Food Sci. 35, 590-592. 

Measuring the content of primary oxidation products is limited due to the transitory nature of peroxides. Yet, their presence may indicate a potential for later formation of sensorially objectionable compounds. The peroxide content increases only when the rate of peroxide formation exceeds that of its destruction. In cases where peroxide breakdown is as fast as or faster than peroxide formation, monitoring lipid peroxides is not a good indicator of oxidation. This can occur in frying oils and sometimes in meat products, particularly in cooked meats where iron is very active and peroxide breakdown is quite rapid. Because the acceptability of an oil or lipid-containing food product depends on the degree to which oxidation has progressed, the simultaneous detection of primary and secondary lipid oxidation products helps to better characterize lipid quality. It is... 

Static headspace GC involves heating the sample in an air-tight environment until the volatile lipids in the food reach an equilibrium with those in the surrounding air. The air above the sample (headspace) is then sampled and analyzed. Flame ionization detection (GC-FID) can be used for quantification and mass-selective detection (GC-MS) can be used for compound identification. This protocol also outlines semiquantitative and quantitative approaches for determination of volatile lipid concentration, and is particularly designed for analysis of a meat sample. 

Shahidi, F. 1994. Assessment of lipid oxidation and off-flavour development in meat and meat products. In Flavour of Meat and Meat Products (F. Shahidi, ed.) pp. 247-266. Chapman and Hall, Glasgow, U K. 

The intensity of undesirable sensory notes has been positively correlated with the content of carbonyl compounds formed through lipid autoxidation reactions. In general, the carbonyl compounds present have the greatest impact on flavor owing to their low flavor thresholds in comparison with hydrocarbons, substituted furans, and alcohols. Aldehydes are major contributors to the loss of desirable flavor in meats because of their rate of formation during lipid oxidation and low flavor threshold. Thus, an alternative approach for monitoring the extent of lipid oxidation in fats and oils is to measure... 

Crackel, R.L., Gray, J.I., Pearson, A.M., Booren, A.M., and Buckley. D.J. 1988. Some further observations on the TBA test as an index of lipid oxidation in meats. Food Chem. 28 187-196. 

Sorensen, G. and Jorgensen, S.S. 1996. A critical examination of some experimental variables in the 2-thiobarbituric acid (TBA) test for lipid oxidation in meat products. Z. Lebensm. Unters. Forsch. 202 205-210. 

In meats, of course, there are components which arise from the protein which cannot be present in the products from pure fat. Table III shows some of the sulfur compounds and aromatic compounds which are also found in irradiated meats. Many of these can be postulated as arising from direct bond cleavage of amino acid moieties. Benzene and toluene may come from phenylalanine and phenol and p-cresol from tyrosine. Recent studies have been directed to considering the origin of some of the compounds from proteinaceous substances. Some of the sulfides, disulfides, and mercaptans can derive directly from cysteine or methionine, but those containing more than two carbon atoms in a chain require more than a superficial explanation. In order to evaluate the contribution of the volatiles from the protein as well as the lipid constituents of meat, volatile components produced in various protein substances have also been analyzed. 

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