Protein gel

Protein aggregation during food preparation plays a significant role in structure fonnation of many gel-type or emulsion-type products [239]. Ferry [240] described protein gelation as the result of structure unfolding that exposes reactive sites, intermolecular aggregation, and eventual formation of infinite, crosslinked gel networks As the conformation of proteins is modified under the influence of heat, protein-protein interactions become more prevalent with formation of covalent and non covalent bonds. Covalently bonded proteins may be considered crosslinked different protein molecules can stick together or protein molecules can bind non protein components [241]. 

As for large oligomeric proteins like those found in vegetal tissues, an early effect produced by heats is dissociation into subunits [242,243]. Because of the 

Protein unfolding implies increased hydrophobicity and partial loss of tertiary and quaternary structure with major effects on functional properties [247] other factors, like chain flexibility, could justify [248-250] the differences between various protein species. 

Food scientists working with biologic tissues usually encounter mixed proteins in the concentration range of 5-20%. The use of concentrated protein solutions maximizes protein-protein interactions and results in calorimetric data with a marked dependence on water content. 

There is some evidence that protein molecules in high concentrations do not unfold totally, since the protein-protein interactions overwhelm the ability of the protein to compete for water hydrogen bonds. We can say that proteins in food are water -plasticizable amorphous polymers. In fact a number of proteins are not water soluble, but they become plasticized by water in the amorphous state. 

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McMillan RA, Conticello VP (2000) Synthesis and characterization of elastin- mimetic protein gels derived from a well-defined polypeptide precursor. Macromolecules 33 4809 821... 

Walkenstrom, P., Windhab, E., and Hermansson, A. M. (1998). Shear-induced structuring of particulate whey protein gels. Food Hydrocolloids 12, 459 68. 

Breci, L., Hattrup, E., Keeler, M., Letarte, J., Johnson, R., Haynes, PA. (2005). Comprehensive proteomics in yeast using chromatographic fractionation, gas phase fractionation, protein gel electrophoresis, and isoelectric focusing. Proteomics 5, 2018-2028. 

O Shaughnessy RF et al. PA-FABP, a novel marker of human epidermal transit amplifying cells revealed by 2D protein gel electrophoresis and cDNA array hybridisation. FEBS Lett 2000 486 149-154. 

If the gel separates DNA and the DNA is detected with a DNA probe, it is called a Southern blot. If RNA is separated on the gel and then detected by a DNA probe, it is a Northern. A Western uses specific antibodies to detect specific protein molecules on a blot of a protein gel. In the Western blot, the role of the DNA probe is filled by an antibody that recognizes a specific protein. 

L. Breci, E. Hattrup, M. Keeler, J. Letarte, R. Johnson, and P. A. Haynes. Comprehensive Proteomics in Yeast Using Chromatographic Fractionation, Gas Phase Fractionation, Protein Gel Electrophoresis, and Isoelectric Focusing. Proteomics, 5(2005) 2018-2028. 

Figure 4. SDS-polyacrylamide gel electrophoresis of microsomes from variously pretreated rainbow trout (A), control microsomes, 90 fig protein/gel (B), /3-naphthoflavone-inauced microsomes, 90 fig protein/gel (C), Aroclor 1242-induced microsomes, 90 fig protein/gel.

Figure 5. Densitiometric scans of electrophoretograms of hepatic microsomes from rainbow trout pretreated with polychlorinated biphenyl congeners (A), control microsomes, 90 fig protein/gel (B), 2,2, 4,4 -tetrachlorobiphenyl-induced microsomes, 90 fig protein/gel (C), 3,3, 4,4 -tetrachlorobiphenyl-induced microsomes, 90 fig protein/gel (D), Aroclor 1242-induced microsomes, 90 fig protein/ gel. The slab gels were stained with Coomassie Blue-250 and individual sample tracts were cut out and scanned at 550 nm. The vertical broken line is at 57,000...

Thompson D, Larson G. 1992. Western blots using stained protein gels. Biotechniques 12 656-658. 

Protein gels show the combined effect of both acid and basic groups in the acid range they behave as polybase gels and in the alkaline range... 

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