Functional aspects of blood plasma proteins 4. Elucidation of the mechanism of gelation of plasma and egg albumen proteins

Abstract

The mechanism of gelation of plasma and egg albumen proteins in a cake-type model system was elucidated by chemical modification, polyacrylamide gel electrophoresis and electron microscopy. It was demonstrated by chemical modification that gelation via disulphide bonds was predominant in all the plasma and egg albumen proteins. Hydrophobic and hydrogen bonds also prevailed in the plasma protein gels. In contrast the breakdown of hydrophobic and hydrogen bonds increased the strength of egg albumen gels. Electrophoretic characterization confirmed that most of the component proteins of plasma and egg albumen were modified chemically. Electron micrographs of the gels of plasma, egg albumen and a mixture of these proteins revealed a generally similar type of network structure, and indicated the compatibility of these proteins. The plasma gels had a more dense network, however, than the egg albumen gels and this was reflected in their correspondingly greater gel strength.examined by measuring the changes in the gel strength and breaking strength of gels before and after chemical treatment.The chemically modified proteins were characterized by polyacrylamide gel electrophoresis to ascertain which of the component proteins were modified. Furthermore, other types of reducing agents, namely, sodium nitrite, sodium sulphite, ascorbic acid and the protease enzyme, trypsin, were selected to study the gelling behaviour of commercial plasma and egg albumen proteins. A brief study of porcine plasma and egg albumen proteins by electron microscopy was also undertaken in the hope of further elucidating the mechanism of gelation. Materials and methodsProteins. Those used were as follows: commercial porcine plasma, Regalbumin (Regal Food Ltd., Dublin); porcine serum (Howell & Lawrie, 1983); porcine plasma ion exchange fractions I, I1 and I11 to be referred to as Fr I, Fr I1 and Fr I11 (Howell & Lawrie, 1983); and spray-dried egg albumen.Chemicals. These were from various sources: cysteine hydrochloride; urea; sodium dodecyl sulphate (SDS), sodium nitrite; sodium sulphite; /3-mercaptoethanol; ascorbic acid and trypsin. Chemical and enzymic modiJication and gelationEach of the chemical reagent, (namely 1% (w/w) cysteine hydrochloride, 4 M urea and 3% (wlw) SDS) was added to the proteins in 45% (w/w) sucrose solutions. In these, the concentrations of commercial porcine plasma, porcine serum, porcine plasma fractions, or egg albumen was 6% (w/w). The mixture of plasma protein and egg albumen contained 3% (w/w) of each. The protein solutions containing the reagent were kept at 20°C for 24 hr to enable maximum modification of the proteins prior to gelation at 95°C for 20 min in tubes according to the method by Howell (1981). The gels were tested on the Tnstron Tester as described previously (Howell & Lawrie, 1983). Control experiments using protein solutions without the reagents were also performed. Eight replicates were used for each test. Changes in the gel strength and breaking strength brought about the reagent were expressed as an int...

Effect of non-meat proteins on hydration and textural properties of pork meat gels enhanced with microbial transglutaminase

“…Hermansson (1982) found that gelation of BP proteins begins at temperatures above that of meat protein gelation. Howell and Lawrie (1985) reported that below 79 1C BP produced heat reversible gels consisting of linear polymer chains and stabilized by weak non-covalent, hydrophobic and electrostatic linkages. The fact that BP proteins in a meat batter form a gel too late in the process to be integrated into the meat protein gel structure may results in mixed gels which are weaker than gels formed by meat proteins alone.…”

Protein interactions in reduced-fat and full-fat Cheddar cheeses during melting

“…The combined use of dissociating agents have been studied by several researchers (Li & Lee,1996;Sheard, Ledward, & Mitchell,1984), who reported a synergistic effect between SDS and mercaptoethanol based on the combined effect of intermolecular disulfide bond formation and hydrophobic interaction. Howel and Lawrie (1985) reported a considerable reduction in gel strength and breaking strength of whole blood in the presence of mercaptoethanol and urea.…”

“…It has been thought that chemical reagents which block the formation of bond between proteins would provide a means of testing which bonds are involved in aggregate formation and in proteineprotein interactions. For example, mercaptoethanol reduces disulfide bonds, urea and sodium dodecyl sulfate (SDS, CH 3 e(CH 2 ) 11 eSO 4 À Na þ ) break hydrogen bonds between NH and CO groups and hydrophobic interactions, and EDTA (ethylenediaminetetraacetic) acid breaks ionic bonds involving calcium salts (Howel & Lawrie, 1985;Lorient, 1979;Melander & Horvath, 1977;Parnell-Clunies, Kakuda, Irvine, & Mullen,1988). The non-ionic molecules of urea, which binds to water via hydrogen bonds at high concentrations, disrupt the usual aqueous hydrogen-bond network.…”

Studies on the electrostatic interactions of lysozyme with α‐lactalbumin and β‐lactoglobulin

“…Most studies to date have been empirical and have displayed interesting and technologically useful phenomena such as synergistic behaviour to increase the gel strength or foaming properties of proteins or phase separation of protein mixtures which has been applied in the formulation of low fat products (Howell & Lawrie, 1985;Howell & Taylor, 1991). However the exact mechanisms for these interactions are not clear.…”