Effect of refrigeration on texture of meat 45 sufficient amounts of the contractile fuel, adenosine triphosphate(ATP), for forcible shortening to set in as the temperature falls below 11C, the most severe effect occurring at about 3 C. Cold- shortening first became apparent in New Zealand, when tough lamb began to be produced routinely by the improved refrigeration techniques which were introduced after the Second World War(Locker, 1985). The shortening phenomenon was first observed scientifically by Locker and Hagyard (1963)and the resulting extremely tough meat after cooking by Marsh and Leet (1966).The mecha- nism of cold shortening has been well described by Bendall(1974)and Jeacocke(1986)and forms the basis of the next sections of this chapter. 3.1.1 Mechanism of shortening The characteristic pattern of post-mortem chemical change, found in all the skeletal muscles of the mammals so far investigated, is shown in Fig. 3.1 The figure has an arbitrary timescale, because although the pattern is irtually constant its duration is highly temperature dependent. Relative time scales can be interpolated from the temperature data in Fig. 3.2 It can be seen in Fig 3. 1 that the supply of contractile fuel (ATP)remains constant and high for some time. It is kept topped up by two resynthetic processes that counteract its slow wastage in the resting muscle. The first of 7.0 6.5 ig. 3.1 Biochemical changes during the course of rigor mortis. Arrow 1 indicates onset of rapid decline of ATP, and arrow 2 the time for half-change of ATP. The time scale is arbitrary and highly temperature dependent(see Fig 3.2)(source: Bendallsufficient amounts of the contractile fuel, adenosine triphosphate (ATP), for forcible shortening to set in as the temperature falls below 11 °C, the most severe effect occurring at about 3 °C. ‘Cold-shortening’ first became apparent in New Zealand, when tough lamb began to be produced routinely by the improved refrigeration techniques which were introduced after the Second World War (Locker, 1985). The shortening phenomenon was first observed scientifically by Locker and Hagyard (1963) and the resulting extremely tough meat after cooking by Marsh and Leet (1966). The mecha￾nism of cold shortening has been well described by Bendall (1974) and Jeacocke (1986) and forms the basis of the next sections of this chapter. 3.1.1 Mechanism of shortening The characteristic pattern of post-mortem chemical change, found in all the skeletal muscles of the mammals so far investigated, is shown in Fig. 3.1. The figure has an arbitrary timescale, because although the pattern is virtually constant its duration is highly temperature dependent. Relative time scales can be interpolated from the temperature data in Fig. 3.2. It can be seen in Fig. 3.1 that the supply of contractile fuel (ATP) remains constant and high for some time. It is kept topped up by two resynthetic processes that counteract its slow wastage in the resting muscle. The first of Effect of refrigeration on texture of meat 45 100 50 7.5 7.0 6.5 6.0 5.5 pH PC 1 2 0 3 4 5 6 7 8 9 Time (arbitrary) PC or ATP as % initial value pH ATP 1 2 Fig. 3.1 Biochemical changes during the course of rigor mortis. Arrow 1 indicates onset of rapid decline of ATP, and arrow 2 the time for half-change of ATP.The time scale is arbitrary and highly temperature dependent (see Fig. 3.2) (source: Bendall, 1974)