Sugars and polyols stablize proteins against heat denaturation. Scanning calorimetry was used to obtain a quantitative estimate of the degree of stabilization. Solutions of ovalbumin, lysozyme, conalbumin, and alpha-chymotrypsinogen were heated at a constant rate, and the temperature of the maximum rate of denaturation was estimated (Tm). Addition of a sugar or polyol raised Tm. The magnitude of the stabilizing effect (delta Tm) depended on both the nature of the protein and the nature of the sugar or polyol, ranging from 18.5 degrees C for lysozyme at pH 3 in the presence of 50% (w/w) sorbitol to 0 degrees C for conalbumin at pH 7 in 50% glycerol solution. It is argued that this stablization is due to the effects of sugars and polyols on hydrophobic interactions. The strength of the hydrophobic interaction was measured in model systems in sucrose and glycerol solutions. Sucrose and glycerol strengthened the pairwise hydrophobic interaction between hydrophobic groups; however, they reduced the tendency for complete transfer of hydrophobic groups from an aqueous to a nonpolar environment. The extent of stabliziation by different sugars and polyols is explained by their different influences on the structure of water. The difference between the partial molar volume of the sugar or polyol and its van der Waals volume was used as a rough quantitative measure of the structure-making or structure-breaking effect. There was a linear relationship between this quantity and delta Tm.

Increased thermal stability of proteins in the presence of sugars and polyols

(1974). Aromatic Contributions To Circular Dichroism Spectra Of Protein. CRC Critical Reviews in Biochemistry: Vol. 2, No. 1, pp. 113-175.

Aromatic contributions to circular dichroism spectra of proteins.

A method is described for the adsorption of selected macromolecules to colloidal gold which is then used as an electron dense marker for the indirect detection of specific cell surface molecules. Membrane bound concanavalin A, which binds specific sugars on horseradish peroxidase, and wheat germ agglutinin, which binds specific sugars on ovomucoid are detected indirectly with gold labeled horseradish peroxidase and ovomucoid, respectively. Goat anti-human IgM on blood lymphocytes is detected with gold labeled rabbit anti-goat IgG. In the preparation of colloidal gold labeled proteins, the problems of flocculation of colloidal gold by proteins and nonadsorption of proteins to colloidal gold, are solved through a combination of concentration of protein and pH variable adsorption isotherms, which allows one to determine the conditions for adsorption of proteins to colloidal gold. Adsorption is pH dependent, the pH conditions correlating with the isoelectric point(s) of the major protein fraction(s); adsorption is influenced by interfacial tension, solubility and by the electrical charge on the molecules. Colloidal gold is inexpensive and preparation of a useful label is rapid, reproducible and the results easily quantitated from electron micrographs.

Adsorption of horseradish peroxidase, ovomucoid and anti-immunoglobulin to colloidal gold for the indirect detection of concanavalin A, wheat germ agglutinin and goat anti-human immunoglobulin G on cell surfaces at the electron microscopic level: a new method, theory and application.

Hen egg white proteins have been extensively utilized as ingredients in food processing because of their unique functional properties, such as gelling and foaming. This review article describes the molecular basis for the development of these functional properties during processing, as well as studies of the development of new methods for improving the functional properties of egg white proteins. The theory that egg white proteins are capable of existing in a ‘molten globule state’, which partially explains their functional properties, is also discussed.

Recent advances in the understanding of egg white protein functionality

Glycoproteins of Cell Surfaces A COMPARATIVE STUDY OF THREE DIFFERENT CELL SURFACES OF THE RAT

Batch purification of ovomucoid and characterization of the purified product.

The heat denaturation of egg white and its component proteins was studied by differential scanning calorimetry. At a heating rate of 10 °C/min, egg white at pH 7 shows two major endotherms, at 65 °C and 84 °C, produced by the denaturation of conalbumin and ovalbumin, respectively. The conalbumin endotherm is increased to 70 °C by raising the pH to 9.0, or 77 °C by addition of aluminium at neutral pH. Addition of sucrose stabilises all the proteins; at 10%sucrose, all endotherms are shifted 2 °C to higher temperatures. Within experimental error, the enthalpy of denaturation of egg white equals the sum of the enthalpies of denaturation of its component proteins, and is independent of pH over the pH range 7–9.

A differential scanning calorimetric study of the stability of egg white to heat denaturation.

The presence of S-ovalbumin, a more heat-stable form of ovalbumin formed on storage of eggs, can be determined by differential scaning calorimetry of egg white. At a heating rate of 10°C/min, at pH 9, the characteristic denaturation temperature of ovalbumin is 84.5°C, that of S, ovalbumin, 92.5°C. The formation of S-ovalbumin proceeds through a previously unrecognised intermediate species having a denaturation temperature of 88.5°C. The kinetics of the conversion on storage of eggs at 4, 22 and 37°C have been determined. Differential scanning calorimetry is a rapid and convenient method of determining the quality of eggs held in storage. Freeze-dried preparations of ovalbumin stored in the cold for 20 years showed partial conversion to the intermediate, but not to S-ovalbumin.

Carol J. Mapes

Papers

Batch purification of ovomucoid and characterization of the purified product.

A differential scanning calorimetric study of the stability of egg white to heat denaturation.

A differential scanning calorimetric study of conversion of ovalbumin to S-ovalbumin in eggs

Dissociation of chicken egg-white macroglobulin into subunite in acid. Hydrodynamic, spectrophotometric, and optical rotatory measurements.

Aldehydes in Poultry Chiller Water