New recommendations for measuring collagen solubility

• Hill's (1966) conditions for collagen solubility tests have no physiological basis.
• % Collagen solubility varies with pH and ionic strength of bathing media.
• % Relaxation of isometric tension is highest at low pH and at low ionic strength.
• Onset temperature of collagen shrinkage varies with bathing solution.
• 30.8 mM NaCl, 1.2 mM KCl in a 10 mM buffer (pH 5.6) is recommended for future work.

The heat-solubility of intramuscular collagen is usually conducted in 1/4 Ringer's solution at pH 7.4, despite this ionic strength and pH being inappropriate for post-rigor meat. The current work studied the percentage of soluble collagen and hydrothermal isometric tension characteristics of perimysial strips on bovine semitendinosus muscles in either 1/4 Ringer's solution, distilled water, PBS, or a solution of the same salt concentration as 1/4 Ringer's but at pH 5.6. Values of % soluble collagen were lower at pH 7.4 than 5.6. Increasing ionic strength reduced % soluble collagen. The maximum perimysial isometric tension was independent of the bathing medium, but the percent relaxation was higher at pH 7.4 than at pH 5.6, and increased with ionic strength of the media. It is recommended that future measurements of collagen solubility and tests on connective tissue components of post-rigor meat should be carried out in a solution of concentrations NaCl and KCl equivalent to those in 1/4 Ringer's, but at pH 5.6, a pH relevant to post-rigor meat.