Microbiology of refrigerated meat 1 oxygen(50-100%)along with 15-50% carbon dioxide to restrict the growth of Pseudomonas and related species(Nottingham, 1982). The microflora of meat stored in commercially used modified atmosphere packs(MAP) is in general similar to that of vacuum packs( Varnam and Sutherland, 1995).At temperatures below 2C, LAB are dominant, Leuconostoc spp. being the most important. Br. thermosphacta, Pseudomonas spp and Enterobacter- aceae are more prevalent in MAP (modified atmosphere packs)than vacuum packs at storage temperatures ca 5C, rather than 1C. Br. ther- mosphacta is relatively CO2 tolerant and the presence of O2 permits growth of this bacterium at pH values below 5. 8. Prior conditioning in air favours the growth of these bacteria, they are also more prevalent in pork than other meats(Dainty and Mackey, 1992). The spoilage of meat in MAP may involve souring similar to that in vacuum-packed meat. Other characteris- tics include'rancid' and'cheesy odours Chemical rancidity does not appear to be primarily involved and souring is probably caused by the metabolites of LAB or Br. thermosphacta(Varnam and Sutherland, 1995) 1.2.2.3 Spoilage of frozen meat Micro-organisms do not grow below ca. -10.C, thus spoilage is only nor mally relevant to handling before freezing or during thawing. In these contexts, frozen meats behave like their unfrozen counterparts, although growth rates may be faster after thawing, owing to drip Although Salmonella, Staphylococci, and other potential pathogens can survive freezing and frozen storage, the saprophytic flora(spoilage bacte ria)tend to inhibit their growth( Varnam and Sutherland, 1995). During freezing and thawing of food, the temperature favours the growth of psychrophilic organisms, most of which are spoilage organisms. Hence, in nearly all cases, if a frozen product is mishandled, spoilage is apparent before the food becomes a health hazard In the past, carcass meats were imported at temperatures of -5 to 10C. At these temperatures there were problems with the growth of psy- chrotrophic moulds such as strains of Cladosporium, Geotrichum, Mucor Penicillium, rhizopus and Thamnidium, causing whiskers'orspots'of various colours depending on the species. Since little meat is now stored at these temperatures mould spoilage is largely of historic importance subject in great detail at microbiology textbooks continue to discuss this Despite this, many mea 1.1.3 Relative humidity Historically low relative humidities(RH) have been recommended to extend shelf-life. Schmid(1931) recommended a storage temperature for meat of 0C and an RH of 90%. Haines and Smith(1933) later demon- strated that lowering the rh is more effective in controlling bacterial growth on fatty or connective tissue than on lean meat. This was due to a slower rate of diffusion of water to the surface. low rh was moroxygen (50–100%) along with 15–50% carbon dioxide to restrict the growth of Pseudomonas and related species (Nottingham, 1982). The microflora of meat stored in commercially used modified atmosphere packs (MAP) is in general similar to that of vacuum packs (Varnam and Sutherland, 1995). At temperatures below 2 °C, LAB are dominant, Leuconostoc spp. being the most important. Br. thermosphacta, Pseudomonas spp. and Enterobacteri￾aceae are more prevalent in MAP (modified atmosphere packs) than vacuum packs at storage temperatures ca. 5 °C, rather than 1 °C. Br. ther￾mosphacta is relatively CO2 tolerant and the presence of O2 permits growth of this bacterium at pH values below 5.8. Prior conditioning in air favours the growth of these bacteria, they are also more prevalent in pork than other meats (Dainty and Mackey, 1992). The spoilage of meat in MAP may involve souring similar to that in vacuum-packed meat. Other characteris￾tics include ‘rancid’ and ‘cheesy’ odours. Chemical rancidity does not appear to be primarily involved and souring is probably caused by the metabolites of LAB or Br. thermosphacta (Varnam and Sutherland, 1995). 1.1.2.2.3 Spoilage of frozen meat Micro-organisms do not grow below ca. -10 °C, thus spoilage is only nor￾mally relevant to handling before freezing or during thawing. In these contexts, frozen meats behave like their unfrozen counterparts, although growth rates may be faster after thawing, owing to drip. Although Salmonella, Staphylococci, and other potential pathogens can survive freezing and frozen storage, the saprophytic flora (spoilage bacte￾ria) tend to inhibit their growth (Varnam and Sutherland, 1995). During freezing and thawing of food, the temperature favours the growth of psychrophilic organisms, most of which are spoilage organisms. Hence, in nearly all cases, if a frozen product is mishandled, spoilage is apparent before the food becomes a health hazard. In the past, carcass meats were imported at temperatures of -5 to -10 °C. At these temperatures there were problems with the growth of psy￾chrotrophic moulds such as strains of Cladosporium, Geotrichum, Mucor, Penicillium, Rhizopus and Thamnidium, causing ‘whiskers’ or ‘spots’ of various colours depending on the species. Since little meat is now stored at these temperatures mould spoilage is largely of historic importance. Despite this, many meat microbiology textbooks continue to discuss this subject in great detail. 1.1.3 Relative humidity Historically low relative humidities (RH) have been recommended to extend shelf-life. Schmid (1931) recommended a storage temperature for meat of 0 °C and an RH of 90%. Haines and Smith (1933) later demon￾strated that lowering the RH is more effective in controlling bacterial growth on fatty or connective tissue than on lean meat. This was due to a slower rate of diffusion of water to the surface. Low RH was more Microbiology of refrigerated meat 11