Some observations on protein changes in washed myofibrils of bovine muscle

It was found that the protein and water contents of washed myofibrils obtained from bovine longissimus dorsi muscles vary with the rate of pH change during the first hour post mortem. Neither myosin nor actin is responsible for the variation, which is due to changes in the other myofibrillar components. The amount of remaining myofibrillar proteins (RMP), obtained after the sum of myosin and actin is deducted from the total myofibrillar protein (TMP), shows a minimum at a rate of pH change corresponding to a 1-h pH value of 6·7. Apart from this pH-dependent decrease, a further substantial reduction of the RMP fraction was observed, particularly in myofibrils extracted from electrically stimulated muscles. It is considered that the observed changes result from partial proteolysis taking place in muscle during the early hours post mortem. A possible involvement of connectin as a primary substrate for the action of calcium-activated neutral protease is discussed. On the basis of the observed correlation between Warner-Bratzler peak shear force and TMP, a significant influence of pre-rigor muscle status on meat tenderness is suggested.