Some Properties of the Fibrillar Proteins of Normal and Watery Pork Muscle

Abstract

SUMMARYIt is shown that the washed muscle fibrils obtained from watery pork have a lower water retention at low ionic strength, and much lower extract‐ability at high ionic strength, than the fibrils from normal pork. These changes are accompanied by a gain of protein by the washed watery fibrils, and this protein originates from the soluble sarcoplasmic proteins. All the changes, including the characteristic gain of protein, can be artificially induced in normal meat by allowing it to pass into rigor at 37° C. The isoelectric region, or region of minimum swelling of watery fibrils, whether washed or unwashed, is similar to or slightly lower than that of normal fibrils. There is a broad isoelectric zone in both cases, extending from ∼pH 5 to ∼5.70. On the other hand, the IP of fully coagulated fibrils lies between 5.6 and 6.1. Washed and unwashed fibrils of watery meat show about the same degree of swelling at all pH values. Normal fibrils, however, show a higher water retention in the unwashed state than the washed. This effect is not due to the Mg or Ca ions included in the unwashed samples, but may result from interaction between the sarcoplasmic and fibrillar proteins. In the unwashed state, the swelling of normal fibrils is nearly double that of the watery fibrils at all pH values.It is shown that the rise of pH in intact carcasses of watery meat as they cooled from 37 to 10° C was probably due to the effect of temperature on the pK of ionizable groups of the proteins and buffering substances. It can be reproduced artificially and reversibly in native and coagulated minced meat, merely by raising or lowering the temperature. The titration curves of watery fibrils show similar titration constants (pK') to those of normal fibrils, but a loss of ratable groups. Heat coagulation, on the other hand, results not only in a bigger loss of titratable groups but in a much larger shift in the titration constants. These results can be interpreted to show that the fibrillar proteins of the watery fibrils are not denatured or aggregated in the usual sense, but are probably covered by a layer of denatured sarcoplasmic protein that is firmly‐bound to the surface of the myofilaments.