10 Meat refrigeration Br. thermosphacta 口 Lactobacillus Fig. 1. 2 Effect of temperature on the rates of anaerobic growth of bacteria on meat slices(source: Newton and Gill, 1978) Leuconostoc. Lactococcus spp are much less common. LAB are able to grow at low temperatures and low O2 tensions and tolerate COz. Psy chrophilic species of Clostridium have been recognised as a significant potential problem( Varnam and Sutherland, 1995). Both Br. thermosphacta and Sh putrefaciens are favoured by high pH values. Sh. putrefaciens is unable to grow below pH 6.0 during storage at low temperatures, whereas Br. thermosphacta is unable to grow anaerobi cally below pH 5.8(Gill, 1983). At temperatures below 5C, Enterobacte- riaceae are inhibited in vacuum packs by CO2, low pH and lactic acid. At higher temperatures and pH values, CO2 is markedly less inhibitory and growth is possible, in particular by Serratia liquefaciens and Providencia spp arnam and Sutherland, 1995) The predominant type of spoilage in vacuum-packed chilled meat is souring(Sofos, 1994; Varnam and Sutherland, 1995). This is not normally detectable until bacterial numbers reach &logocfucm- or greater. The exact cause of such spoilage is unknown, but is assumed to result from lactic acid and other end-products of fermentation by dominant LAB High-PH (DFD) vacuum-packed meat spoils rapidly and involves the production of rge quantities of hydrogen sulphide(H2s) by Sh putrefaciens and Enter bacteriaceae (Gill, 1982; Varnam and Sutherland, 1995). Characteristic greening'occurs owing to H2s combining with the muscle pigment to give green sulphmyoglobin; the meat also develops putrid spoilage odours (Gill, 1982) &. Packaging in various gaseous atmospheres has been used as an alterna- ve to vacuum packing. The intention has been to preserve the fresh meat colour and to prevent anaerobic spoilage by using high concentrations ofLeuconostoc. Lactococcus spp. are much less common. LAB are able to grow at low temperatures and low O2 tensions and tolerate CO2. Psy￾chrophilic species of Clostridium have been recognised as a significant potential problem (Varnam and Sutherland, 1995). Both Br. thermosphacta and Sh. putrefaciens are favoured by high pH values. Sh. putrefaciens is unable to grow below pH 6.0 during storage at low temperatures, whereas Br. thermosphacta is unable to grow anaerobi￾cally below pH 5.8 (Gill, 1983). At temperatures below 5 °C, Enterobacte￾riaceae are inhibited in vacuum packs by CO2, low pH and lactic acid. At higher temperatures and pH values, CO2 is markedly less inhibitory and growth is possible, in particular by Serratia liquefaciens and Providencia spp. (Varnam and Sutherland, 1995). The predominant type of spoilage in vacuum-packed chilled meat is souring (Sofos, 1994; Varnam and Sutherland, 1995). This is not normally detectable until bacterial numbers reach 8 log10 cfu cm-2 or greater. The exact cause of such spoilage is unknown, but is assumed to result from lactic acid and other end-products of fermentation by dominant LAB. High-pH (DFD) vacuum-packed meat spoils rapidly and involves the production of large quantities of hydrogen sulphide (H2S) by Sh. putrefaciens and Enter￾obacteriaceae (Gill, 1982; Varnam and Sutherland, 1995). Characteristic ‘greening’ occurs owing to H2S combining with the muscle pigment to give green sulphmyoglobin; the meat also develops putrid spoilage odours (Gill, 1982). Packaging in various gaseous atmospheres has been used as an alterna￾tive to vacuum packing. The intention has been to preserve the fresh meat colour and to prevent anaerobic spoilage by using high concentrations of 10 Meat refrigeration 15 10 5 2 0 10 20 30 40 50 60 Generation time (h) Temperature (°C) Br. thermosphacta Enterobacter Lactobacillus Fig. 1.2 Effect of temperature on the rates of anaerobic growth of bacteria on meat slices (source: Newton and Gill, 1978)