Egg lipids

The ratio between the amounts of azelaic and palmitic acids (A/P) is a parameter for differentiating drying oils from egg lipids in paint samples because the amount of dicarboxylic acid formed in the ageing of egg lipids is considerably less than it is in drying oils. Values of A/P >1 indicate a drying oil, values of A/P <0.3 are typical of egg lipids,... 

Evaluating the P/S ratio requires particular care first, because of the presence of mixtures of more than one binder, such as egg and oil in tempera grassa secondly, due to the presence of waxes, and in particular beeswax, which has been widely used as a coating and restoration material and thirdly, due to the contribution of FAs from other sources such as fouling or micro-organisms, which can considerably alter the P/S values from those expected for reference materials. For instance, because the ratio for walnut oil falls between the value of linseed oil, poppy oil and egg lipids, using the P/S ratio it is not possible to differentiate between pure walnut oil, and mixtures of linseed and poppy oil or egg. 

Other common forms of spoilage in mayonnaise are a result of oxidative degradation of various components, especially vegetable oil and egg lipids. Microbial... 

Fig. 41. Time-resolved emission spectra for TNS bound to egg lipid at 20 °C. Early spectrum time delay (At) = 0 gate width (8t) = 2.5 ns. Late spectrum At = 31 ns, 6t = 2.5 ns...

How might species differences in egg lipid content and the timing of yolk consumption affect POP deposition into developing embryos or larval fish Before addressing this issue, a brief overview of egg biochemistry and yolk dynamics in fish embryos and larvae is warranted. 

Given the large interspecies differences in toxicity to some POPs, how relevant is it to consider maternal transfer of POP to the offspring Is it relevant to consider differences in egg-lipid content and absorption of lipid We think these factors are relevant both for predicting toxicity and for consideration of interspecies differences in exposure (particularly within target tissues) to POP in the field. Understanding the dynamics of POP transfer and uptake could provide insight into susceptibility of certain species such as eel, or on the other extreme, cod, to POP exposure. 

In sum, despite the little work that has been conducted on interspecies differences in total body lipid, lipid distribution and egg lipid, we feel it is a potentially important topic for predicting vulnerabilities to POPs in field-caught fish. Improved understanding of tissue lipid dynamics and lipid composition is likely to be important in any target species selected for field study of POP exposure and effects. 

Lai et al. (1986) studied the compressibility as a measure of flowability of egg lipid and co-dried carbohydrate and salt, as a function of temperature, moisture, and lipid content. Temperature increased compressibility, resulting from the ability of the cohesive powder bed to maintain an open structure supported by the interparticle forces. These softened, plasticized, and extremely weak structures collapsed under very small pressures giving rise to the measured compressibility. Lipid removal neither improved flowability nor yielded reliable results in compressibility. 

In careful examinations, Rhodes and Lea (1957) obtained the composition of phospholipids. Here, for the first time, lysophospholipids were shown to be natural components of egg lipids and not artifacts produced during sample preparation, as the authors explicitly point out. The PC fraction contains 0.9% plasmalogens the cephalin fraction contains 0.2% phosphatidylserines. Table 14.3 gives an overview of the composition of phospholipids in egg yolk. There is high agreement between the results of all individual authors. Only the results of Holopainen (1972) for sphingomyelins appear to be too high. 

When feed contains higher quantities of PUFA, as in fish or algae oil supplements, the content of linoleic acid and other polyunsaturated FA increases significantly. Even the linoleic acid content of the feed is involved in the amount of unsaturated FA in the egg yolk. Supplements of oils containing linoleic acid, such as safflower, flax, soybean, sunflower, and com (maize) oil, lead to high enrichment of this acid in the egg lipids (Biedermann et al., 1971). 

Among the sterols of the egg, which make up approximately 4% of egg lipids, cholesterol predominates. It occurs only in the egg yolk, mainly in a free form. Only 4 to 15% are esterified with FA (Chung et al., 1965). The FA compositions of the cholesteryl esters are shown in Table 14.2. 

Arachidonic acid, of considerable importance as a precursor of the prostaglandins, thromboxanes and leukotrienes (Section 1.4), is present at low levels in many fish oils and at higher levels in animal fats (mainly phospholipids). It is usually isolated from liver or egg lipids. Though rare in the plant kingdom it has been identified in some mosses and ferns and is a major component of marine algae. 

Belton RJ, Jr., Adams ML, Foltz KR. 2001. Isolation and characterization of sea urchin egg lipid rafts and their possible function during fertilization. Mol Reprod Dev 59(3) 294-305. 

We have achieved good separation of polyunsaturated fatty acid esters from saturated, monosaturated and disaturated fatty acid esters and this has been used as a means of identifying the presence of polyunsaturates, especially fish oil, in samples (Fig. 1.2). However, if there is a considerable amount of trienoic fatty acids in the mixture, as in egg lipids, the separation is not very pronounced (Shantha and Ackman, 1991a). Nakamura, Fukuda and Tanaka (1996) have used similar TLC separation of marine lipids and were able to quantitate the amount of pol)amsaturated fatty acids by using scanning densitometry followed by Coomassie blue staining. 

The three carbonyl spectra of egg lipids illustrated in Figs 4.20(a)-(c) demonstrate the pathway of co-3 fatty acids in triglycerides and phospholipids. The eggs are enriched with co-3 fatty acids by a special hen feed. Nearly all co-3 fatty acids are found in the phospholipids, the highest amounts in phosphatidylethanolamine (PE) (Diehl et aL, 1996a). 

Figure 4.20 NMR spectra of egg lipids (a) DHA egg oil (b) phosphatidylcholine fraction of DHA egg oil (c) phosphatidylethanolamine fraction of DHA egg oil. DHA = 4,7,10,13,16,19- docosahexaenoic acid. Instrument details are given in text. Section 4.10.

The efficiency of ME utilisation for egg synthesis in laying hens has been estimated to be in the range 0.60-0.80, with a mean value of 0.69. For egg protein synthesis the efficiency is estimated to be 0.45-0.50, and for egg lipids 0.75-0.80. The synthesis of body tissue in laying hens is also highly efficient (0.75-0.80). 

The fatty acid composition of the lipids depends on that of the feed (Table 11.12). However, the extent to which individual fatty acids are incorporated varies greatly. The addition of fats rich in linoleic acid to the feed, e. g., soy oil, leads to a great increase in this fatty acid. In comparison, only traces of the main fatty acid 10 0 of coconut oil is recovered (Table 11.12). Highly unsaturated (0-3-fatty acids (20 5, 22 6) from fish oils do appear in egg lipids, but not in proportion to their... 

About 4% of the egg lipids consists of sterols. The main corrqtonent is cholesterol (96%), ca. 15% of which is esterified with fatty acids. The cholesterol content is 2.5%, based on the egg yolk solids. Disregarding mammalian brain, this level exceeds hy far that in all other foods (cf. 3.8.2.2.1) and, therefore, serves as an indicator of the addition of eggs. Cholestanol, 7-cholestenol, campesterol, P-sitosterol, 24-methylene cholesterol and lanosterol are other components of the sterol fraction. The quality of egg products is endangered hy autoxidation of cholesterol (cf. 3.8.2.2.1). 

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