The fat content and adiabatic heating impact the lethality of high pressure processing towards Escherichia coli

High hydrostatic pressure processing (HHP) is used to reduce or eliminate pathogens and spoilage bacteria in food. The aim of this study was to investigate the effect of fat on the pressure resistance of E. coli in beef and a yogurt model system. Ground beef and pH-adjusted (pH 5.5) yogurt were adjusted to a fat content from 3 to 35% with adipose tissue and cr & egrave;me fraiche, respectively, and inoculated with E. coli. Samples were treated at 600 MPa and 20 or 30 degrees C for 3 min. Sample temperatures were adjusted prior to compression to compensate adiabatic heating, or not. An increased fat content of ground beef decreased the pressure resistance of E. coli. This was observed irrespective of the temperature history of the treatment. For example, at 20 degrees C, an increase in fat content from 15.5 to 24.4% increased treatment lethality by 6 log CFU/g for E. coli MG 1655. The correction for adiabatic heating increased or decreased pressure resistance at 20 degrees C in a strain-specific manner. Addition of cr & egrave;me fraiche to pH-adjusted yogurt did not alter the pressure resistance of E. coli (strains MG 1655 and DM 18.3), or increased resistance (E. coli AW 1.7 and AW 1.3). In summary, the pressure resistance of E. coli is dependent on the fat content, the food matrix and the temperature trajectory during processing. The effect of adipose tissue in meat matrix links the fat content of meat to lipid oxidation and the oxidative stress response.