Cholesterol in egg yolk

The adaptation of methods for lipid extraction and quantification by colorimetric determination of either ester or cholesterol in egg yolk with some contamination of egg white is described. Results are compared with those obtained by a conventional enzymatic determination. 

Pasin, G., Smith, G.M., and O Mahony, M. 1998. Rapid determination of total cholesterol in egg yolk using commercial diagnostic cholesterol reagent. Food Chem. 61 255-259. 

Traditional mayonnaise is an 80% oil-in-water emulsion, which may rely on mustard seeds for solid particle stabilization. Two constituents of egg yolk, lecithin and cholesterol, are surfactants, which promote the formation of oil-in-water and water-in-oil emulsions, respectively. The ratio of lecithin to cholesterol in egg yolk favors the water-in-oil type but the final emulsion type formed is due to the action of mustard seed, which favors an oil-in-water emulsion (Petrowski, 1976). 

Nnhitional methods can also be applied to enriching egg yolk lipids with CLA by administering it in adequate doses with feed. However, the effectiveness of nnhitional methods in the reduction of cholesterol in egg yolk lipids is low. The nse of 3-hydroxy-3-methylglutarylo-CoA reductase for this purpose is more effective. In this way, the cholesterol level in egg yolk lipids can be decreased by 30% however, this has consequences in the layers prodnctivity (Pisnlewski et al., 2001 Pszczola et al., 2000). 

Figure 4.4 NMR spectra quantification of cholesterol in egg yolk lecithin with use of internal standard (I.S.) (a) pure sample (detail) (b) pure sample plus I.S. (c) CH3 signals of the cholesterol reference. Instrument details are given in text. Section 4.10. (Source Spectral Service, unpublished material.)...

Calibration plots of peak area versus nanograms spotted had a linearity correlation coefficient value of 0.98 or greater. Standards were spotted with samples to provide an individual calibration plot for each plate. Scans of duplicate sample aliquots are also shown in Fig. 9. The cholesterol values of 20 egg yolk samples determined by quantitative TLC ranged from 9.7 to 26.2 mg/g (avg 12 mg/g), which is similar to the values reported in the literature for cholesterol in egg yolk from various birds. See Reference 87 a for an update of this study. 

Similarly, removal of cholesterol from liquid egg yolk using /1-cyclodextrin has been reported. This involved the formation of an insoluble complex by binding with cholesterol in the oil-water interface of egg yolk. As the amount of added /1-cyclodextrin increased, the cholesterol removal efficiency was increased but valuable nutrients of egg yolk also decreased. As a result, it was concluded that the molar ratio of 3 1 5 1 for /l-cyclodextrin cholesterol was most effective at removing cholesterol from egg yolk [49]. 

Morgan J.N., Armstrong, D.J. 1992. Quantification of cholesterol oxidation products in egg yolk powder spray-dried with direct heating. J. Food Sci. 57, 43-45. 

Besides phospholipid composition, the main difference between plant/legume lecithin (e.g., soy) and lecithin in egg yolk is that the former has a higher unsaturated fatty acid content and no cholesterol. Egg lecithin as a commercial ingredient, with the exception of some medical feeding programs, is too expensive for routine use in food (10). In some infant formulas, egg yolk lipids and egg lecithin are used (22). 

Cyclodextrin inclusion compounds have found application in pharmacology, the food industry, and cosmetics. Typical examples are the solubilization of insulin and steroids, the removal of cholesterol from egg yolk, and the conservation of basis notes in perfumes by slow release rates of rose oil and similar ingredients. Chemical stabilization of oxygen-sensitive compounds, e.g., the sulfides of onions and garlic flavor, and of vitamins is also achieved by cyclodexteins. 

Ginzberg, A. et al. (2000). Chickens fed with biomass of the red microalga Porphyridicum sp. have reduced blood cholesterol level and modified fatty acid composition in egg yolk, J. Appl. PhycoL, 12, 325. 

The nntritional modihcation of egg yolk lipids primarily involves an increase in the concenhation of mono- and polyenoic fatty acids and a decrease in the cholesterol concentration. Feeding layer diets with increased concentrations of olive oil rich in Ci81 acid resnlted in an increase of this acid in the egg yolk lipids. However, the best resnlts in terms of an increase in the concenhation of PEFA in egg yolk lipids were obtained by snpplemenhng feed with hsh oils or seaweed biomass rich in these acids. 

Milk is an emulsion ofbutterfat droplets in an aqueous mixture of sugars, mineral salts and proteins. Ice cream is another emulsion with a similar composition. The emulsifying agents in both emulsions are proteins with smaller amounts of phospholipids, mainly lecithin. In egg yolk, the emulsifying agents are phospholipids and cholesterol. 

Lecithin, a common name for PC, is a natural emulsifier found in egg yolk. It is present in bile and helps prevent the formation of gallstones by stabilizing bile cholesterol. In addition, lecithin present in bile excreted into the intestine aids in fat digestion. Lecithin is widely used in foods such as margarines and salad dressings to stabilize the fat components, thus preventing the separation of the fat and water components. In addition, lecithin is used in non-food products such as soaps, paints and cosmetics (Brown, 1990). 

Imitation whole egg having a low cholesterol content contains egg white as a base nonfat milk and vegetable oil, substituting for egg yolk, are added to give a composition similar to whole egg. These are in frozen, Hquid, or dried forms. 

Low cholesterol egg products are formed by extraction of cholesterol from the egg. Attempts have been made to extract cholesterol by using hexane or by supercritical CO2 extraction methods (24,25). A whole egg product in which 80% of the cholesterol is removed by a process using beta-cyclodextrin, a starch derivative, added to egg yolks has been introduced. The cyclodextrin binds up to 80% of the cholesterol, the mixture is centrifuged, and the Hquid separated. The cholesterol-reduced yolk is then blended with egg white, pasteurized, and packed in asceptic containers to give a Hquid whole egg product having a shelf Hfe of 60 days under refrigeration (see Eood packaging). 

The basis for contrast agents derived from nutrional products was Intralipid, which had been prepared from phospholipids obtained from soy bean oil and egg yolk [86]. Intralipid was chemically modified by iodination into Intraiodol, which contained 50 mgl mbThe particles formed in the emulsion were mostly taken up by the hepatocytes and to a lesser extent by the RES [87,88]. Intraiodol was better tolerated than EOE-13 or its precursor, AG 60.99. The addition of cholesterol to Intraiodol resulted in NRI 757 with an iodine concentration of 42 mg mL b Further modifications by replacing the iodinated triglycerides of Intraiodol by ethiodized poppy seed oil and reducing the cholesterol content to... 

Cholesterol-rich lipoproteins of the LDL type are particularly important in the development of arteriosclerosis, in which the arterial walls are altered in connection with an excess plasma cholesterol level. In terms of dietary physiology, it is important that plant foodstuffs are low in cholesterol. By contrast, animal foods can contain large amounts of cholesterol—particularly butter, egg yolk, meat, liver, and brain. 

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