The spoilage characteristics of Brochothrix thermosphacta and two psychrotolerant Enterobacteriacae in vacuum packed lamb and the comparison between high and low pH cuts.

The spoilage potential of Brochothrix thermosphacta, Serratia proteamaculans and Rahnella aquatilis was investigated in vacuum packaged high (5.9 to 6.4) and low (5.4 to 5.8) pH lamb. Vacuum packaged fore shank (m. extensor carpi radialis) and striploins (m. longissimus dorsi) (n=306) inoculated with ~100 CFU of individual bacteria were stored for twelve weeks at temperatures -1.5, 0, 2 and 7°C. Spoilage characteristics and bacterial numbers were recorded and analysed in comparison to un-inoculated control samples. All three bacterial species were shown to grow in vacuum packaged lamb of pH values between 5.4 and 6.4, when stored at chilled temperatures (-1.5 to 7°C) for up to 84 days. B. thermosphacta and S. proteamaculans caused spoilage to the meat under these conditions whilst R. aquatilis spoiled high pH meat at 7°C. These results go against previous beef models stipulating that Brochothrix and Enterobacteriacae species cannot grow on or cause spoilage of low pH meat in the absence of oxygen.