Immunolocalisation of intermediate filament proteins in porcine meat. Fibre type and muscle-specific variations during conditioning

Two intermediate filament proteins, desmin and vinculin, were immunofluorescently localised in porcine longissimus dorsi⁷ and iliocostalis muscles up to 7 days post mortem. Changes in tenderness of the m. longissimus and the water-holding capacity of both muscles were also monitored throughout this storage period. Longissimus muscle shows a rapid decline in the overall intensity of labelling for both desmin and vinculin. In contrast to the vinculin labelling, desmin labelling is preferentially lost from type IIB muscle fibres in the longissimus muscle. In the redder iliocostalis muscle, the loss of desmin and vinculin labelling was less rapid and did not show an obvious relation to muscle fibre type. In one sample with very high water loss, there were indications of greater extracellular space development and delayed loss of intermediate filament labelling. The time course of diminishing intermediate filament labelling is consistent with previous suggestions that degradation of these proteins is involved in post-mortem conditioning. The variations within and between muscles shown here may explain some of the variability in their mechanical properties. Additionally, it is suggested that intermediate filament integrity is necessary for the expulsion of water from the muscle cells during drip formation.