Effects of storage and the presence of a beef microflora on the thermal resistance of Salmonella Typhimurium DT104 in beef and broth systems

To investigate the effects of storage and the presence of a beef microflora on the thermal resistance of Salmonella serotype Typhimurium DT104 on beef surfaces and in a broth system during subsequent heat treatments after extended low-temperature storage (4°C for 14 days) or mild temperature abuse (10°C for 7 days). Surviving Salm. Typhimurium DT104 cells were estimated after heating in a water bath (55°C) by plating beef and broth samples on tryptone soya agar and overlaying with xylose-lysine-deoxycholate agar. In beef and broth systems, D₅₅ values for Salm. Typhimurium DT104 stored at 4°C or 10°C in the presence or absence of a beef microflora were significantly lower (P < 0·01) than the D values for this organism heat-treated immediately after inoculation. In beef systems, the D₅₅ values were significantly lower (P < 0·05) in the presence of a beef microflora than the D₅₅ values obtained in 'pure' culture under all temperature/storage combinations. However, in broth systems, there was no significant difference between the D₅₅ values obtained in 'pure' culture and the D₅₅ values obtained from systems containing beef microflora. Storage of Salm. Typhimurium DT104 significantly reduced the thermal resistance of the pathogen in beef and broth systems. In the presence of high numbers of a Gram-negative beef microflora, the heat sensitivity of the pathogen was further increased on beef surfaces but not in broth. Studies investigating the survival of Salm. Typhimurium DT104 in different food systems will help define safe food preservation processes and will aid in the elimination this pathogen from the food production environments.