Swelling of Aquatic Animal Muscles-I
Influence of pH
1953 Volume 19 Issue 3 Pages 178-184
Details
1953 Volume 19 Issue 3 Pages 178-184
In order to obtain in a simple method knowledge of hydration of fish muscle which plays an important role in behavior of the muscle proteins, a series of research has to be carried out on swelling of muscle. In the present study, effect of pH on swelling of comminuted muscle is examined. Degree of swelling (S) is expressed by volume percentage of sedimentary muscle in a mixture of I part muscle and 3 parts water after centrifuged.
In case of horse mackerel muscle, on either side of an isoelectric zone (about 5.0-6.0), addition of HCl up to about pH 4.5, or of NaOH up to about pH 9.5 occasions very pronounced swelling. Further addition of acid or alkali causes slight peptization and the swelled muscle shows weak fluidity (Fig. 1).
KCl, added so as to 0.5 M solution, suppresses swelling of muscle caused by HCl below an apparent isoelectric point, pH 5.5 (pH for the minimum swelling), but above pH 5.5, it exerts an exactly opposite effect, namely, very marked increase in swelling is observedin presence of salt (Fig.4).
From these facts it is deduced that swelling of muscle cannot be explained simply on basis of osmotic pressure alone, but it seems to have a close relation with hydration of muscle proteins, especially that of myosin. Because solubility of myosin'rises on the alkaline side, while decreases on acid side of isoelectric point in presence of salt. (7)
According to the nature of anions or cations, different kinds of acids or bases vary in their effects upon the swelling. For instance, H2SO4 (Fig. 2) and Ba (OH)2 (Fig. 3) which both interact with the proteins as a bivalent ion, do not cause so marked swelling as HCl or NaOH.
When compared the swelling of horse mackerel muscle with those of sardine, carp, and skip-jack, no appreciable differences are observed among the behaviors of their swelling. On the other hand, the muscle of squid behaves differently from the other fish muscles in the following ways: (1) its isoelectric point (pH 4.8) is lower than that of the others (pH 5.5), (2) marked swelling is observed between 5.5 and 8.5, (3) when pH stands outside of this renge, considerable peptization of the proteins occurs to form a viscous solution (Fig. 5).
