The properties of glycerol-extracted Longissimus dorsi muscle fibres and myofibrils taken from beef carcasses during post-mortem conditioning

Abstract Muscle samples from beef Longissimus dorsi (LD) were conditioned inv vacuo at 10°C for up to 21 days and then stored in a glycerol-extracted state at −20°C to determine how their mechanical properties were altered by the conditioning process. Muscle fibres were progressively more difficult to dissect as conditioning proceeded, but those dissected showed isometric mechanical tension in the presence of Ca 2+ , relaxation in the absence of Ca 2+ and calcium sensitivity which did not vary with conditioning up to 8 days. Myofibrils prepared from the same conditioned tissue showed slight changes with conditioning time, namely an initial rise in Ca 2+ -activated ATPase followed by a later fall, a slow rise in ATPase in the absence of Ca 2+ and an increase in Ca 2+ -sensitivity. It is concluded that preparation of muscle fibres from conditioned tissue selects undamaged fibres, and that conditioning proceeds by the progressive increase in number of conditioned fibres within each of which conditioning has taken place relatively rapidly.