Drip production in meat refrigeration 29 2.1.4 ce formation in muscle tissues In general, freezing and thawing exacerbate drip loss through damage the muscle structure. It is necessary to differentiate between the effects freezing in pre-rigor and post-rigor muscle. For most practical purposes, meat is in the latter condition but there has been considerable interest the rapid freezing of hot,, 1. e. pre-rigor meat. 2.1.4.1 Pre-rigor muscle The freezing of meat immediately after slaughter appears at first sight to be an excellent method of overcoming many of the chilling, hygiene and storage problems of conventional production methods. However, there are wo problems, ' cold shortening thaw rigor', that result in very tough meat and that have to be overcome to make such a process viable. Thaw rigor, or ' thaw contractor' as it is sometimes called, also significantly ncreases drip loss after thawing If the meat temperature falls below 10C before the supply of fuel for ontraction, i.e. ATP, is used up, but freezing has not occurred, the muscle will contract. This phenomenon called'cold shortening was first described by Locker and Hagyard (1963) and is discussed in Chapter 3 of this book. The protein denaturation that results from cold shortening produces a large amount of drip(offer et al., 1988) If very high rates of heat extraction can be achieved, then the meat can be frozen fast enough to stop cold shortening. However, in this case,a more severe shortening, thaw rigor, will occur during thawing. In unre- strained muscle up to 25% of the muscle weight will be lost in the form of drip during thawing(Bendall, 1974). Bendall stated that the problems associated with thaw rigor could be overcome by holding the frozen meat at-3 to -5C for at least 48h. However, such a process is not used commercially 2.1.4.2 Post-rigor muscle Chemical changes after slaughter cause the acidity of the tissue to increase and the pH falls to a level which is normally in the range of 5.5-5.7. This compares with a pH of about 7.0-7.2 in the living tissue. One of the conse quences of this fall in pH is a change in the permeability of the sarcolemma which now permits sarcoplasmic proteins and water to pass more readily out of the cell(Voyle, 1974). When the tissue is slowly cooled below its freezing point, this protein-containing fluid is extracted from the cell to con tribute to the growth of extracellular ice crystals. Loss of fluid from the cell results in an increase in the intracellular salt concentration This in turn causes some denaturation of those proteins remaining within the cell. more rapid rate of freezing will cause the intracellular water, including that in the actin-myosin lattice, to crystallise2.1.4 Ice formation in muscle tissues In general, freezing and thawing exacerbate drip loss through damage of the muscle structure. It is necessary to differentiate between the effects of freezing in pre-rigor and post-rigor muscle. For most practical purposes, meat is in the latter condition but there has been considerable interest in the rapid freezing of ‘hot’, i.e. pre-rigor meat. 2.1.4.1 Pre-rigor muscle The freezing of meat immediately after slaughter appears at first sight to be an excellent method of overcoming many of the chilling, hygiene and storage problems of conventional production methods. However, there are two problems, ‘cold shortening’ and ‘thaw rigor’, that result in very tough meat and that have to be overcome to make such a process viable. Thaw rigor, or ‘thaw contractor’ as it is sometimes called, also significantly increases drip loss after thawing. If the meat temperature falls below 10 °C before the supply of fuel for contraction, i.e. ATP, is used up, but freezing has not occurred, the muscle will contract. This phenomenon called ‘cold shortening’ was first described by Locker and Hagyard (1963) and is discussed in Chapter 3 of this book. The protein denaturation that results from cold shortening produces a large amount of drip (Offer et al., 1988). If very high rates of heat extraction can be achieved, then the meat can be frozen fast enough to stop cold shortening. However, in this case, a more severe shortening, thaw rigor, will occur during thawing. In unre￾strained muscle up to 25% of the muscle weight will be lost in the form of drip during thawing (Bendall, 1974). Bendall stated that the problems associated with thaw rigor could be overcome by holding the frozen meat at -3 to -5 °C for at least 48 h. However, such a process is not used commercially. 2.1.4.2 Post-rigor muscle Chemical changes after slaughter cause the acidity of the tissue to increase and the pH falls to a level which is normally in the range of 5.5–5.7. This compares with a pH of about 7.0–7.2 in the living tissue. One of the conse￾quences of this fall in pH is a change in the permeability of the sarcolemma which now permits sarcoplasmic proteins and water to pass more readily out of the cell (Voyle, 1974). When the tissue is slowly cooled below its freezing point, this protein-containing fluid is extracted from the cell to con￾tribute to the growth of extracellular ice crystals. Loss of fluid from the cell results in an increase in the intracellular salt concentration. This in turn causes some denaturation of those proteins remaining within the cell. A more rapid rate of freezing will cause the intracellular water, including that in the actin–myosin lattice, to crystallise. Drip production in meat refrigeration 29