138 Meat refrigeration show a favourable effect from faster freezing rates. Mittal and Barbut (1991) showed that freezing rate affected the modulus of rigidity of meat after cooking. Similar values to fresh meat were produced in meat frozen in liquid nitrogen. The value of the modulus increased as the rate of freez ing decreased. In 1980 Anon and Calvelo reported a relationship between the rate of freezing and drip loss, drip loss reaching a maximum when the freezing time from-1 to-7C was ca 17 min Mascheroni (1985)used this relationship to produce a method for determining the rate at which frozen meat had been frozen. However, attempts to replicate the work at Langford(James et al., 1983)were unsuccessful because of the variability in drip loss from meat before freezing. Studies using differential scanning calorimetry (dSC) on fresh and frozen bovine muscle at different freezing rates show a decrease of denaturation enthalpies; the slower the freezing rate the greater the loss(Wagner and Anon, 1985). Investigations covered freezing times from 5 to 60min Experiments with pork M. longissimus dorsi found no difference in drip loss between samples frozen at -20oC or -80oC(Sakata et al., 1995). At -20 and"C samples took 6 and 3h, respectively to pass from -lC to ca.-6'C In the -20C samples inter- and intracellular ice were seen but only intracellular ice was seen at-80C. Methods of freezing clearly affect the ultrastructure of muscle. Slow freezing(1-2mmh- for example( Buchmuller, 1986)tends to produce large ice crystals extracellularly, whilst quick freezing (e.g. 50mmh-)gives smaller crystals in and outside cells(Buchmuller, 1986: Bevilacqua et al 1979). Obviously a temperature gradient will occur in large pieces of meat and result in a non-uniform ice morphology(Bevilacqua et al., 1979) Petrovic et al. (1993)found that slowly frozen meat, 0.22 and 0.39cmh- lost more weight during freezing, thawing and cooking than that frozen at 3.95-5.66cmh-(Table 7.1). However, higher weight losses during thawing were measured at an intermediate freezing rate of 3. 33 cm-. Meat frozen at rates of 3.33 cmh and faster was rated as more tender and juicier after cooking than unfrozen controls and slow frozen samples (Table 7.2). Petro- vic et al. stated that the optimal conditions for freezing portioned meat are those that achieve freezing rates between 2 and 5cmh-to-7oC Grujic et al.(1993)suggest even tighter limits, 3.33-3.95cmh-. Slow freezing at up to 0.39cmh- resulted in decreased solubility of myofibrillar proteins, increase in weight loss during freezing, thawing and cooking, lower water- binding capacity and tougher cooked meat. Very quickly frozen meat (4.9cmh-)had a somewhat lower solubility of myofibrillar proteins, lower yater-binding capacity and somewhat tougher and drier meat. The samples were thawed after storage times of 2-3 days at -20oC so the relationship etween freezing rates and storage life was not investigated Storage times of 48h and 2.5 months were used during investigations of the effect of different freezing systems and rates on drip production fromshow a favourable effect from faster freezing rates. Mittal and Barbut (1991) showed that freezing rate affected the modulus of rigidity of meat after cooking. Similar values to fresh meat were produced in meat frozen in liquid nitrogen. The value of the modulus increased as the rate of freez￾ing decreased. In 1980 Añón and Calvelo reported a relationship between the rate of freezing and drip loss, drip loss reaching a maximum when the freezing time from -1 to -7 °C was ca. 17 min. Mascheroni (1985) used this relationship to produce a method for determining the rate at which frozen meat had been frozen. However, attempts to replicate the work at Langford (James et al., 1983) were unsuccessful because of the variability in drip loss from meat before freezing. Studies using differential scanning calorimetry (DSC) on fresh and frozen bovine muscle at different freezing rates show a decrease of denaturation enthalpies; the slower the freezing rate the greater the loss (Wagner and Añón, 1985). Investigations covered freezing times from 5 to 60 min. Experiments with pork M. longissimus dorsi found no difference in drip loss between samples frozen at -20 °C or -80 °C (Sakata et al., 1995). At -20 and -80 °C samples took 6 and 3h, respectively to pass from -1 °C to ca. -6 °C. In the -20 °C samples inter- and intracellular ice were seen but only intracellular ice was seen at -80 °C. Methods of freezing clearly affect the ultrastructure of muscle. Slow freezing (1–2 mm h-1 for example (Buchmuller, 1986) tends to produce large ice crystals extracellularly, whilst quick freezing (e.g. 50 mm h-1 ) gives smaller crystals in and outside cells (Buchmuller, 1986; Bevilacqua et al., 1979). Obviously a temperature gradient will occur in large pieces of meat and result in a non-uniform ice morphology (Bevilacqua et al., 1979). Petrovic et al. (1993) found that slowly frozen meat, 0.22 and 0.39 cmh-1 , lost more weight during freezing, thawing and cooking than that frozen at 3.95–5.66 cmh-1 (Table 7.1). However, higher weight losses during thawing were measured at an intermediate freezing rate of 3.33 cm h-1 . Meat frozen at rates of 3.33 cm h-1 and faster was rated as more tender and juicier after cooking than unfrozen controls and slow frozen samples (Table 7.2). Petro￾vic et al. stated that the optimal conditions for freezing portioned meat are those that achieve freezing rates between 2 and 5 cmh-1 to -7 °C. Grujic et al. (1993) suggest even tighter limits, 3.33–3.95 cm h-1 . Slow freezing at up to 0.39 cmh-1 resulted in decreased solubility of myofibrillar proteins, increase in weight loss during freezing, thawing and cooking, lower water￾binding capacity and tougher cooked meat. Very quickly frozen meat (>4.9 cmh-1 ) had a somewhat lower solubility of myofibrillar proteins, lower water-binding capacity and somewhat tougher and drier meat. The samples were thawed after storage times of 2–3 days at -20 °C so the relationship between freezing rates and storage life was not investigated. Storage times of 48 h and 2.5 months were used during investigations of the effect of different freezing systems and rates on drip production from 138 Meat refrigeration