Egg white denaturation

Why does egg white denature when cooked but remain liquid at room temperature ... 

Proteins of egg white denature more rapidly than those of whey protein concentrate (13, 34). However, isolated p-lactoglobulin from the whey concentrate was more susceptible to surface denaturation than egg white ovalbumin. These data suggest that whey contains substances that protect the proteins from surface denaturation and may account for the lower stability of whey protein concentrate foams than those of egg white protein. A balance between the disaggregation effect of select pH values and the tendency toward greater aggregation of proteins at higher heating temperatures were correlated closely with maximum foam stability (13, 15). 

The mechanical denaturation of proteins occurs, for example, when whipping egg whites. Denatured proteins located at the interface with the air have a positive effect on foam stabihty. During the heat treatment of eggs, white protein denaturation begins at temperatures around 57 °C. In the temperature range 60-65 °C,... 

Denaturation is accompanied by changes in both physical and biological properties. Solubility is drastically decreased, as occurs when egg white is cooked and the albumins unfold and coagulate. Most enzymes also lose all catalytic activity when denatured, since a precisely defined tertiary structure is required for their action. Although most denaturation is irreversible, some cases are known where spontaneous renaturation of an unfolded protein to its stable tertiary structure occurs. Renaturation is accompanied by a full recovery of biological activity. 

Denaturation is a term used to describe the change of structure of protein molecules in solution. The addition of heat or a decrease of pH are methods of denaturing or changing the nature of the protein. An example of denaturation is the hardening of an egg white when the egg is boiled or fried. 

In this activity, egg whites are used as an example of a protein. Denaturing will be accomplished by lowering the pH and by increasing the temperature. 

Observing and Inferring What change of appearance did the egg white undergo when it became denatured ... 

The variation in the performance of different types of egg albumen in different systems is almost certainly caused by variations in the degree of denaturation of the protein. Those products that work best with fresh egg white clearly need an undenatured product. 

Most people prefer their eggs to be lightly boiled, with the yellow yolk still liquid and the albumen solid and white. We say the egg white has been denatured . The variation in egg size is not great. An average egg contains essentially a constant amount of yolk and albumen, so the energy necessary to heat both the yolk and albumen (and to denature the albumen) is, more or less, the same for any egg. 

The value of AH, for denaturing egg white is likely to be quite small, since it merely involves changes in hydrogen bonds. For the purposes of this calculation, we say A Hr has a value of 35 kJmol-1. 

AG3e73 K has a negative value, implying that the reaction at this new, elevated temperature is now spontaneous. In summary, the Gibbs-Helmholtz equation quantifies a qualitative observation the reaction to denature egg white is not spontaneous at room temperature, but it is spontaneous at elevated temperatures, e.g. when the egg is boiled in water. 

Soluble proteins have a more complex structure than the fibrous, completely insoluble structural proteins. The shape of soluble proteins is more or less spherical (globular). In their biologically active form, globular proteins have a defined spatial structure (the native conformation). If this structure is destroyed (denaturation see p. 74), not only does the biological effect disappear, but the protein also usually precipitates in insoluble form. This happens, for example, when eggs are boiled the proteins dissolved in the egg white are denatured by the heat and produce the solid egg white. 

Biotin binds with high af nity (/Cd = 10 M) and specificity to avidin, a protein found in egg white. Since boiling denatures avidin, biotin deficiency only occurs when egg whites are eaten raw. 

Denaturation is the irreversible precipitation of proteins caused by heating, such as the coagulation of egg white as an egg is cooked, or by addition of strong acids, bases, or other chemicals. This denaturation causes permanent changes in the overall structure of the protein and because of the ease with which proteins are denatured it makes it difficult to study natural protein structure. Nucleic acids also undergo denaturation. 

Heat, strong acids or bases, ethanol, or heavy-metal ions irreversibly alter the secondary structure of proteins (see below). This process, known as denaturation, is exemplified by the heat-induced coagulation and hardening of egg white (albumin). Denaturation destroys the physiological activity of proteins. 

Biotin deficiency is rare but under laboratory conditions it can be induced by feeding subjects with large amounts of raw egg white which contains the protein, avidin, which has a binding site for the imidazole moiety of biotin, thus making it unavailable. Avidin is denatured by heat and, therefore, biotin binding occurs only in raw egg albumen. Symptoms of biotin deficiency include scaly dermatitis, hair loss, loss of appetite, nausea, hallucinations and depression. 

As long as egg white is kept cool, it. stays transparent and almost liquid. But what happens when you heat it You know from frying or boiling an egg It hardens — coagulates — into a solid white mass which you can not again dissolve in water. The chemist s term for this change is denaturation — the egg white has changed its nature. 

An interesting side effect of the presence of ovatransferrin in egg whites is the custom, long established before any rational explanation, of beating egg whites in copper bowls to stabilize the foam (as in meringues, etc.) The copper complex of ovatransferrin stabilizes the protein of egg white against denaturation and thus Stabilizes the foam.111... 

J Sajdok, D Pozdrkova. P Rauch, J Kas. Thermal denaturation of henn egg white studied by chromatographic and immunological techniques. J Food Sci 54 906-908, 1989. 

Globular proteins - these have complicated three-dimensional structures and are soluble in water. They are easily affected by acids, alkalis and temperature increase, when they are said to be denatured. Casein (in milk), albumen (in egg white) and enzymes are examples of globular proteins. 

R. Nakamura, Studies on the foaming property of the chicken egg white, Part VII, On the foaminess of the denatured ovalbumin, Agr. Biol. Chem. 28 (1964) 403-407. 

An egg white before the denaturation of the albumin protein causes the transucent substance to change in color and viscosity. 

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