Theoretical aspects of water-holding in meat.

As myofibrils consist of a three-dimensional network of long, solid protein particles with the shortest dimension of less than 20 nm, the theoretical foundations of water-holding in meat should be studied from a colloid or surface chemistry point of view. The classical hypotheses for water-holding in meat are based on electrostatic forces or osmotic forces, which cause the swelling of the myofibrils. The more recent research adds to those the structure of water, whether it is low density water induced by kosmotropic effects dominating in the system, or high density water induced by chaotropes, respectively. The phenomena in the one to three molecules thick water layers on protein surfaces do not, however, explain the bulk water-holding.The interactions of ions and non-polar kosmotropes with water and proteins have a relevant effect on water-holding. The chaotropic/kosmotropic effects of different ions will be of importance especially when reducing sodium contents in meat-based foods. Rough estimates of the surface areas of different constituents of the myofibrils showed that transverse elements have larger contact surfaces with the liquid phase than longitudinal. Therefore, more attention should be paid to heavy meromyosin, Z-line and other elements of molecular size or colloidal size. Short range surface forces seem to dominate theories of water-protein interactions, and the theoretical foundations of bulk water-holding are still lacking. Irrespective of the lack of theoretical explanation on the mechanism of water-holding in meat, the meat industry is able to control the macroscopic behaviour of meat-based ingredients rather well.