The role of the endomysium in the salt-induced swelling of muscle fibres

Variable uptake of water is a persistent problem in meat processing. To try to understand the changes that occur during water uptake, and thereby explain this variability, we have measured the swelling of salt-treated single muscle fibres from rabbit longissimus dorsi. By dissolving out the myofibrillar proteins with SDS we have been able to tell whether or not a dissected fibre has an endomysial connective sheath. We find that some fibres do lack a sheath and that these stripped fibres swell on average approximately five times more than intact fibres in 0·25 m KI. This shows that the endomysium limits the swelling of the fibre in salt, as is also shown by the greater swelling of those parts of fibres from which the endomysium has been deliberately removed. On prolonged immersion in 0·25 m KI the stripped parts of fibres shrink after swelling whereas the smaller swelling of unstripped parts is maintained. With careful, slow dissection, the proportion of stripped fibres is low at all times post mortem, but if a quicker method is used, the proportion of stripped fibres increases with time post mortem. As ageing proceeds, an increasing incidence of transverse fractures reduces the productivity of the quicker method, so the slow method has to be used. Regardless of the method of dissection the swelling of stripped and unstripped fibres does not depend on time post mortem. Thus it is the changing proportion of stripped fibres that underlies the earlier report (Wilding et al. Meat Sci., 1986 18 , 55) of a dependence of swelling on time post mortem. The ease of stripping of endomysium from muscle fibres may be important in meat processing. Thus whether or not fibres produced during comminution and mixing of meat are stripped directly affects water uptake. The extraction of myofibrillar proteins may also be affected, which would be important for the adhesion of cooked reformed meat products.