Shrinkage gelatine

In the case of the rather porous and flexible structure of sodium caseinate nanoparticles, the data show that the interaction with surfactants causes a tendency towards the shrinkage of the aggregates, most likely due to the enhanced cross-linking in their interior as a result of the protein-surfactant interaction. This appears most pronounced for the case of the anionic surfactants (CITREM and SSL) interacting with the sodium caseinate nanoparticles. Consistent with this same line of interpretation, a surfactant-induced contraction of gelatin molecules of almost 30% has been demonstrated as a result of interaction with the anionic surfactant a-olefin sulfonate (Abed and Bohidar, 2004). 

A common example of syneresis is found when a mold of gelatin remains under refrigeration for a period. A general shrinkage of the body of the gel occurs and a liquid collects around the edge of the mold. Hie liquid is a dilute solution of the original composition. Since the total volume of the system remains (he same, syneresis should not he considered simply as the opposite of imbibition (absorption). Extending the onset of syneresis in various products, notably foods, is of obvious importance. 

The collagen gelatin transformation in solution has been recognized as a reversible first-order phase transition, subject to the same physical laws which govern the crystalline amorphous phase transitions observed in systems of linear polymers. The direct relationship between the transition in solution and the well-known thermal shrinkage phenomenon exhibited by collagen fibers has also been established. 

To investigate this idea, Esipova (1957) and Doty and Nishihara (1958) examined the temperature at which solutions of various types of collagen were transformed to gelatin, and compared these measurements of T with thermal shrinkage temperatures obtained by Gustavson and others. 

FIGURE 3.14 Solution of a model of drying for a shrinking solid. Gelatin plate 3 mm thick, initial moisture content 6.55 kg/kg. Shrinkage coefficient 5 = 1.36. Main plot shows dimensionless moisture content O, dimensionless thickness 5 = R/Rq, solid temperature t. Insert shows evolution of the internal profiles of O. 

Products that set with a large amount of shrinkage should not be used, e.g. gelatine, methyl methacrylate polymerization. 

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