Drip production in meat refrigeration 27 With beef and lamb, provided the chilling regime is adequate, only a little myosin denaturation occurs probably because the carcass is chilled suffi- ciently before a low pH is reached. PSE meat is therefore not usually a problem with these species, except sometimes in the deep muscle if the carcass has been chilled slowly(Offer et aL., 1988) With pork, however, the pH fall is faster, especially in carcasses of stress susceptible animals. In these carcasses, the ph falls to below 6.0 within 45 min of slaughter when the carcass temperature is above 35C. Myosin denaturation may then be extensive and pig carcasses are vulnerable to the PSE state. As well as stress, this condition may be genetically predetermined (Honikel, 1990) PSE is not an all-or-none phenomenon and the drip loss depends on the extent of myosin denaturation. The drip loss can therefore be controlled to some extent by the chilling regime. Frozen PSE meat exhibits excessive drip loss on thawing(Honikel, 1990) 2.1.3 Water relationships in meat In living muscle, 85-95% of the total water is held within the fibres in dynami equilibrium with the remaining 5-15%(plasma water) outside the fibre walls. Within the fibre, the water is held both by the contractile, myofibrillar, filament proteins, myosin and actin, and by the soluble, sarcoplasmic proteins which include myoglobin and the glycolytic enzymes. The water balance is such that it allows movement of the proteins within the fibre and exchange of metabolites in and out of the fibre without altering the overall amount of water held. Therefore, when a force is applied to a pre-rigor muscle, excised immediately after the death of an animal, very little fluid can be squeezed out. The distribution of space in muscle is shown in Table 2.2 Calculations can be made of the diameters of the capillary-like spaces between the filaments of the myofibril and between sarcoplasmic proteins from which the number of water molecules between nearest-neighbour structures can be deduced. The results are shown in Table 2.3 Table 2.2 Ap ate distribution of th excised muscle Volume as total vol pre-nigor Extrafibre space Intrafibre space 889 Extrafibrillar space 2-24 30-32.5 Intrafibrillar space 5862 ming a 12% reduction in filament lattice volume post rigor. 974With beef and lamb, provided the chilling regime is adequate, only a little myosin denaturation occurs probably because the carcass is chilled suffi- ciently before a low pH is reached. PSE meat is therefore not usually a problem with these species, except sometimes in the deep muscle if the carcass has been chilled slowly (Offer et al., 1988). With pork, however, the pH fall is faster, especially in carcasses of stress￾susceptible animals. In these carcasses, the pH falls to below 6.0 within 45 min of slaughter when the carcass temperature is above 35°C. Myosin denaturation may then be extensive and pig carcasses are vulnerable to the PSE state.As well as stress, this condition may be genetically predetermined (Honikel, 1990). PSE is not an all-or-none phenomenon and the drip loss depends on the extent of myosin denaturation. The drip loss can therefore be controlled to some extent by the chilling regime. Frozen PSE meat exhibits excessive drip loss on thawing (Honikel, 1990). 2.1.3 Water relationships in meat In living muscle,85–95% of the total water is held within the fibres in dynamic equilibrium with the remaining 5–15% (plasma water) outside the fibre walls.Within the fibre, the water is held both by the contractile, myofibrillar, filament proteins,myosin and actin,and by the soluble,sarcoplasmic proteins which include myoglobin and the glycolytic enzymes. The water balance is such that it allows movement of the proteins within the fibre and exchange of metabolites in and out of the fibre, without altering the overall amount of water held. Therefore, when a force is applied to a pre-rigor muscle, excised immediately after the death of an animal, very little fluid can be squeezed out. The distribution of space in muscle is shown in Table 2.2. Calculations can be made of the diameters of the capillary-like spaces between the filaments of the myofibril and between sarcoplasmic proteins from which the number of water molecules between nearest-neighbour structures can be deduced. The results are shown in Table 2.3. Drip production in meat refrigeration 27 Table 2.2 Approximate distribution of the spaces in excised muscle Structure Volume as % total vol. pre-rigor post-rigor Extrafibre space <12 100 Intrafibre space 88–95 Extrafibrillar space 22–24 30–32.5 Intrafibrillar space 66–71 58–62a a Assuming a 12% reduction in filament lattice volume post rigor. Source: Penny, 1974