Effect of prerigor lactic acid treatment on lysosomal enzyme release in bovine muscle

An improved method for isolating intact lysosomes from beef muscle is prese nted, using an unspecific bacterial protease (nagarse, 50 mu g ml(-1)) prio r to homogenisation. Nagarse treatment resulted in 100% increased cathepsin B + L activities in the membrane fraction (subcellular fraction containing lysosomes). By using this method the subcellular distribution of lysosomal enzymes, as affected by parameters related to meat marination, was investi gated in beef muscle. Different prerigor lactic acid treatments were perfor med in a muscle homogenate, in a muscle mince finely cut with scissors, and in whole muscle. The effect of lower pH on the level of free (not bound) e nzyme activities was dependent on muscle integrity. Lowering pH in the musc le homogenate from 7.2 to 5.0 shifted the majority of cathepsin B + L and b eta-glucuronidase activities from the membrane fraction into the myofibrill ar fraction. In contrast, decreased pH of the muscle mince increased enzyme activities in the soluble fraction (P < 0.05). Also the lactic acid inject ion procedure resulted in increased activities of lysosomal enzymes in the soluble fraction (P < 0.01). Storage for up to 4 days resulted in a gradual increase in free enzyme activity also in control samples, but to a lower f inal level as compared to lactic acid treated samples. (C) 1999 Society of Chemical Industry.