212 Meat refrigeration Table 10.3 Storage life and nature of spoilage of vacuum-packaged pork 5°C Storage life Spoilage Storage life (weeks) characteristics characteristics 5.4-5.8 -4 Flavour changes. souring 6.2-6.5 Variable Greening, odour of His, putrefaction Source: Egan et al. 1986. with 12 weeks for normal pH beef (Gill and Penney, 1986). In metalized polyester or aluminium foil laminate vacuum packs, times were 9 and 15 weeks respectively. At a lower temperature Jeremiah et al.(1995a, b) have shown that off-flavour development, coinciding with lactic acid bacteria reaching maximum numbers, currently restricts the storage life of carbon dioxide CO)or vacuum-packaged pork at-15C to 9 weeks. Based on appear ance, CO2-packaged and vacuum-packed pork loin had storage lifes of ove 15 weeks and slightly over 12 weeks, respectively. Only small differences were found between pork loins from dark, firm, dry(DFD): pale, soft exuding(PSE)and normal quality groups. They believed that reducing the current levels of microbial contamination would allow storage life to be extended to meet all domestic and export requirements. Bell et al. (1996) detected no major off odours after 98 days at -01C from hot-boned bull beef that had been cooled and stored in vacuum or CO2 packs. On opening, the appearance of the strip loins was also acceptable. However, overageing as believed to have reduced the retail display life of the meat. The authors thought that the process could produce high quality beef for catering use with a storage life of 70 days. The effect of temperature and packaging was clearly demonstrated by Lee et al.(1985) and Gill and Harrison(1989). Only small changes in micro- bial numbers(Fig. 10.3), pH, drip and off-odour were found in vacuum or vacuum plus gas flushed packs of pork after 49 days storage at-4C ( Lee et aL., 1985), whilst green discolouration was significant after 14 days at 3 and 7C and 28 days at 0C. The amount of drip loss increased substan- tially with both length and temperature of storage(Fig. 10.4). Drip loss from pork liver tends to be higher than that from muscle and increases more rapidly during storage. At a storage temperature of 5C losses increased from 1.9% after 1 day to ca. 6%after 6 days( Strange et al., 1985) Gill and Harrison(1989)found that vacuum-packed cuts of pork longis- simus dorsi muscle( skin on) were grossly spoiled by Brochothrix thermo- sphacta after 2 weeks storage at 3C compared with 5 weeks at-15C. Cuts
with 12 weeks for normal pH beef (Gill and Penney, 1986). In metalized polyester or aluminium foil laminate vacuum packs, times were 9 and 15 weeks respectively. At a lower temperature Jeremiah et al. (1995a, b) have shown that off-flavour development, coinciding with lactic acid bacteria reaching maximum numbers, currently restricts the storage life of carbon dioxide (CO2) or vacuum-packaged pork at -1.5 °C to 9 weeks. Based on appearance, CO2-packaged and vacuum-packed pork loin had storage lifes of over 15 weeks and slightly over 12 weeks, respectively. Only small differences were found between pork loins from dark, firm, dry (DFD); pale, soft, exuding (PSE) and normal quality groups. They believed that reducing the current levels of microbial contamination would allow storage life to be extended to meet all domestic and export requirements. Bell et al. (1996) detected no major off odours after 98 days at -0.1 °C from hot-boned bull beef that had been cooled and stored in vacuum or CO2 packs. On opening, the appearance of the strip loins was also acceptable. However, overageing was believed to have reduced the retail display life of the meat. The authors thought that the process could produce high quality beef for catering use with a storage life of 70 days. The effect of temperature and packaging was clearly demonstrated by Lee et al. (1985) and Gill and Harrison (1989). Only small changes in microbial numbers (Fig. 10.3), pH, drip and off-odour were found in vacuum or vacuum plus gas flushed packs of pork after 49 days storage at -4 °C (Lee et al., 1985), whilst green discolouration was significant after 14 days at 3 and 7 °C and 28 days at 0 °C. The amount of drip loss increased substantially with both length and temperature of storage (Fig. 10.4). Drip loss from pork liver tends to be higher than that from muscle and increases more rapidly during storage. At a storage temperature of 5°C losses increased from 1.9% after 1 day to ca. 6% after 6 days (Strange et al., 1985). Gill and Harrison (1989) found that vacuum-packed cuts of pork longissimus dorsi muscle (skin on) were grossly spoiled by Brochothrix thermosphacta after 2 weeks storage at 3 °C compared with 5 weeks at -1.5 °C. Cuts 212 Meat refrigeration Table 10.3 Storage life and nature of spoilage of vacuum-packaged pork Meat pH 0 °C 5 °C Storage life Spoilage Storage life Spoilage (weeks) characteristics (weeks) characteristics 5.4–5.8 6 Flavour changes, 3–4 Flavour changes, souring souring 6.2–6.5 4–5 Variable 2–3 Greening, odour of H2S, putrefaction Source: Egan et al., 1986
Chilled and frozen storage 213 8 -4° 0 Storage time(days) Fig. 10.3 Growth of psychrotroph counts(logo cfug" )on vacuum-packed cubed ork at-4. 0, 3 and 7"C(source: Lee et al., 1985) 口-4° 0° 旦 口3°c ■7°c Storage time(days) Fig 10.4 Drip loss from vacuum-packed cubes of pork stored at-4.0.3 and 7C (source: Lee et aL., 1985) packed under CO2 spoiled after 5.5 weeks storage at 3C. Growth of Bro- chothrix thermosphacta was suppressed when the pork was stored under CO2 at -15C. Growth of Enterobacteriaceae caused gross spoilage of an increasing proportion of cuts between 18 and 26 weeks. Until spoilage occurred, the eating quality of the pork was little affected by the length of storage. In audits carried out in New Zealand to improve the shelf-life of vacuun cked chilled lamb, changing the chilling practice was found to have the largest effect(Gill, 1987). It was found that the significance of the relatively small numbers of organisms added to carcasses during dressing was greatl magnified by their growth during carcass cooling. Small changes to the chilling practices alone extended the storage life by up to 50%. The length and conditions used during ageing can also affect the storage life of meat Nortje and Shaw, 1989). Beef loin steaks from primals that had been aged
packed under CO2 spoiled after 5.5 weeks storage at 3 °C. Growth of Brochothrix thermosphacta was suppressed when the pork was stored under CO2 at -1.5 °C. Growth of Enterobacteriaceae caused gross spoilage of an increasing proportion of cuts between 18 and 26 weeks. Until spoilage occurred, the eating quality of the pork was little affected by the length of storage. In audits carried out in New Zealand to improve the shelf-life of vacuumpacked chilled lamb, changing the chilling practice was found to have the largest effect (Gill, 1987). It was found that the significance of the relatively small numbers of organisms added to carcasses during dressing was greatly magnified by their growth during carcass cooling. Small changes to the chilling practices alone extended the storage life by up to 50%. The length and conditions used during ageing can also affect the storage life of meat (Nortjé and Shaw, 1989). Beef loin steaks from primals that had been aged Chilled and frozen storage 213 10 8 6 4 2 0 0 7 14 21 28 Storage time (days) –4°C 0 °C 3°C 7°C Log cfu g–1 Fig. 10.3 Growth of psychrotroph counts (log10 cfu g-1 ) on vacuum-packed cubed pork at -4, 0, 3 and 7 °C (source: Lee et al., 1985). 5 4 3 2 1 0 0 7 14 21 28 Storage time (days) –4°C 0 °C 3 °C Drip loss (%) 7°C Fig. 10.4 Drip loss from vacuum-packed cubes of pork stored at -4. 0. 3 and 7 °C (source: Lee et al., 1985)
214 Meat refrigeration for 3 weeks in vacuum packs discoloured more rapidly and off-odours leveloped sooner than those from meat that had been hung in air for one week or vacuum packed for one week. The poorer storage stability was explained by higher initial levels of bacteria because of growth during ageing Rancidity development was only detected in the 3-week-aged steaks that were stored at 6C Studies have also shown that there is an interaction between storage and retail display. The retail display life of pork from CO2 packaged primals depends on the length of time the primals have been stored( Greer et al 1993). On appearance criteria, the display life in days is 4.60-0. 15(weeks in storage), whilst on odour criteria the display life in days is 5.03-0.17 The tenderness, juiciness and flavour of beef patties has been found to deteriorate during chilled storage with the flavour deteriorating less at 0C than at 4 or 8C(Bentley et al. 1989). Drip loss increased with storage temperature from 3.2%at 0C to 3.3% at 4C and 4.6% at 8"C Drip loss was also affected by the type of packaging with greater drip in vacuum packs than in 100% nitrogen or CO2 back-flushed packs. Total plate counts Icreased from 2.7 to 7.2 loglo cfu cm after 7 days and to 8.6loglo cfu after 1 days of storage but no effect of storage temperature or packaging type was detected 10.2.3 Cooked products The influence of temperature on the storage life of vacuum packed sliced cured meat products is shown clearly in Table 10.4 Precooked beef roasts can be stored for 28 days at 4C(Stites et al 1989). The roasts of beef chuck were prepared in vacuum cooking bags with phosphate salt and cooked to a centre temperature of 70C. They were then Table 10.4 Storage life for vacuum-packed sliced cured meat products Temperature Storage life(days) Cooked Cooked 11.5 Source: Bogh-Sorensen et al.. 1986
for 3 weeks in vacuum packs discoloured more rapidly and off-odours developed sooner than those from meat that had been hung in air for one week or vacuum packed for one week. The poorer storage stability was explained by higher initial levels of bacteria because of growth during ageing. Rancidity development was only detected in the 3-week-aged steaks that were stored at 6 °C. Studies have also shown that there is an interaction between storage and retail display. The retail display life of pork from CO2 packaged primals depends on the length of time the primals have been stored (Greer et al., 1993). On appearance criteria, the display life in days is 4.60–0.15 (weeks in storage), whilst on odour criteria the display life in days is 5.03–0.17 (weeks in storage). The tenderness, juiciness and flavour of beef patties has been found to deteriorate during chilled storage with the flavour deteriorating less at 0 °C than at 4 or 8 °C (Bentley et al., 1989). Drip loss increased with storage temperature from 3.2% at 0 °C to 3.3% at 4 °C and 4.6% at 8 °C. Drip loss was also affected by the type of packaging with greater drip in vacuum packs than in 100% nitrogen or CO2 back-flushed packs. Total plate counts increased from 2.7 to 7.2 log10 cfucm-2 after 7 days and to 8.6 log10 cfu after 21 days of storage but no effect of storage temperature or packaging type was detected. 10.2.3 Cooked products The influence of temperature on the storage life of vacuum packed sliced cured meat products is shown clearly in Table 10.4. Precooked beef roasts can be stored for 28 days at 4 °C (Stites et al., 1989).The roasts of beef chuck were prepared in vacuum cooking bags with phosphate salt and cooked to a centre temperature of 70 °C.They were then 214 Meat refrigeration Table 10.4 Storage life for vacuum-packed sliced cured meat products Temperature Storage life (days) (°C) Bologna Smoked Cooked Cooked sausage fillet pork loin pork loin 12 7 – 21 – 8 11.5 9 33 16.5 5 21.5 10 66 31.5 2 33 11.5 78 52.5 0 42 22.5 141 64 -3 11 33 165 >64 Source: Bøgh-Sørensen et al., 1986