Egg-yolk

Egg yolk, which contains several components with emulsifying properties, notably lecithin, is often used in all-natural , premium or homemade ice creams. Egg yolk has the approximate composition (by weight) of 50% water, 16% protein, 9% lecithin, 23% other fat, 0.3% carbohydrate and 1.7% minerals. Lecithin consists of phosphatides and phospholipids. Egg yolk is usually supplied for use in ice cream manufacture either as pasteurized fresh egg yolk, frozen sugared pasteurized egg yolk (which has had about 10% sucrose added to protect it from damage during freezing) or as dehydrated egg yolk. Egg yolk solids are normally used at about 0.5-3%. High concentrations are only used for 

Electrophoretic analyses of the lipid-free samples provide an insight into the proteins and apoproteins (lipoproteins after removal of the hpids, e. g., by extraction with acetone) present in egg yolk and its fractions. A relevant experiment, the results of which are presented in Table 11.9, shows 20 protein zones in the molecular weight 

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Phosphoproieins. Contain phosphates and include casein from milk and phosvilin from egg yolk. 

Phosphorus, like nitrogen, is an essential constituent of living matter where it may be partly in combination (as phosphate groups) with organic groups, for example in lecithin and egg yolk, or mainly in inorganic form, as calcium phosphate(V), in bones and teeth. 

Lecithin. Lecithin [8002-43-5] (qv) is a mixture of fat-like compounds that includes phosphatidyl choline, phosphatidyl ethanolamines, inositol phosphatides, and other compounds (37). Commercial lecithin was originally obtained from egg yolks, but is now extracted from soybean oil. Lecithin is used in many products, including margarine, chocolate, ice cream, cake batter, and bread. 

To be classified as custard or French, product must contain >1.4% egg yolk solids. 

In 1936, biotin was isolated from egg yolks (8), in 1939 from beef Hver (9), and in 1942 from milk concentrates (10). Biotin-producing microorganisms exist in the large bowel but the extent and significance of this internal synthesis is unknown. 

Choline occurs widely in nature and, prepared synthetically, it is available as an article of commerce. Soybean lecithin and egg-yolk lecithin have been used as natural sources of choline for supplementing the diet. Other important natural-food sources include Hver and certain legumes (18—22). 

The yolk is separated from the white by the vitelline membrane, and is made up of layers that can be seen upon careful examination. Egg yolk is a complex mixture of water, Hpids, and proteias. Lipid components iaclude glycerides, 66.2% phosphoUpids, 29.6% and cholesterol [57-88-5] 4.2%. The phosphohpids consist of 73% lecithin [8002 3-5] 15% cephahn [3681-36-7], and 12% other phosphohpids. Of the fatty acids, 33% are saturated and 67% unsaturated, including 42% oleic acid [112-80-1] and 7% linoleic acid [60-33-3]. Fatty acids can be changed by modifying fatty acids ia the laying feed (see... 

Frozen Egg Products. Frozen egg products include egg white, plain whole egg, whole egg with yolk added (ie, fortified), plain egg yolk, fortified whole egg with com symp, sugared egg yolk, salted egg yolk, salted whole egg, and scrambled eggs and omelets. Egg products are frozen in a blast freezer at —40 C for up to 72 h, and then held for storage at —24 C (see Refrigeration and refrigerants). They are used by large and small bakeries and for other uses. 

Gelation of egg yolk occurs below 6 C. When frozen egg yolk is thawed, it has a gel-like consistency and is difficult to handle, requiring special equipment water is sometimes added in order to thin the thawed frozen yolk. Frozen yolk products have ingredients such as sugar or salt added to reduce gelation and improve ease of handling. 

Dried whole egg and yolk products with glucose are less stable, and are usuaUy held under refrigeration until used. The whole egg product has more glucose than the egg yolk and therefore is less stable. 

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). 

Egg yolk contains approximately 17% egg white natural egg yolk contains about 52% soHds. 

Spray dryers may lose dried egg products out of the stack. Cyclone-type coUectors, usually used as the secondary coUector, are not properly designed to coUect products efficiently. A weU-designed cyclone coUector recovers only 85—90% of spray-dried egg white, with 10—15% lost out of the stack, and 94—95% of egg products co-dried with carbohydrates. Bag-type coUectors are needed for 100% recovery of both these products. Plain whole egg and plain egg yolk products are capable of being coUected almost 100% with a cyclone coUector, but a bag coUector is advised (see Airpollution control methods). 

Protein residues, eg, soft-boiled egg yolk, are difficult stains to handle. If the stains are not totally denatured, proteases can decompose them. There are commercial proteases with a high temperature optimum (60°C) that can remove most protein soils in a dishwasher (63). Patents on the use of Upases in ADDs have claimed that Upases can reduce the formation of spots and films on glasses (62,64—66) however, no commercial appUcation of Upases in ADDs has been implemented. 

There is some evidence for chemically mediated endocrine disruption in amphibians. The egg yolk protein, vitellogenin, is inducible in amphibians by exposure to DDT. " Males of the short clawed toad Xenopus laevis given 250 fig/g or 1 fig/g o,p -DDT for seven days have been shown to produce vitellogenin, although the induction was less than that achieved by treatment with 1 fig/g of either 17/1-oestradiol or diethylstilboestrol. Research has also shown that endocrine disrupting chemicals can alter sex ratios in wild populations of certain species PCB congeners and organochlorine compounds have been linked with male domination of sex ratios in polluted compared to unpolluted sites. ... 

Dotter, m. egg yolk, vitellus. — /. any of several plants, BS wild flax. 

Dotter-. yolk, vitelline, -gelb, n. egg yolk, egg yellow. -61, n. gold-of-pleasure oil, camelina (seed) oil. 

Eier, n.pf. eggs, -albumin, n. egg albumin, ovalbumin, -dotter, m. yolk of eggs, -drtise, /. corpus luteum. -frucht,/. eggplant. gang, m. oviduct, -ol, n. egg-yolk oil, egg oil. -pulver, n. egg powder, custard powder, -schale, /. egg shell, -schalenglanz, m. eggshell luster. Stein, m. odlite, egg stone. 

Gelbe, n. yellow (of an egg), yolk. Gelbeisen-erz, n., -stein, m. yellow day ironstone (okriges) yellow ocher copiapite. -kies, m. pyrite. gelbeln, v.i. turn yellowish. 

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