The combined effect of high pressure and storage on the heat sensitivity of Escherichia coli O157:H7

Abstract

Escherichia coli O157:H7, in a laboratory medium, was subjected to a high pressure treatment of 200 MPa for 30 min at 30°C. Heat inactivation studies were carried out at 55, 58 and 60°C on the pressure-treated cells. When the heat inactivation studies were carried out immediately after pressure treatment, the D values obtained indicated that pressure treatment increased the heat sensitivity of E. coli O157:H7. When pressure-treated cultures were stored at 3°C, prior to heat inactivation, the heat sensitisation was found to persist for up to 10 days but was lost after 15 days. When a similar study was carried out using E. coli O157:H7 suspended in skimmed milk, an increased sensitivity to heat was observed immediately after pressure treatment but after storage for 4 days at 3°C there was no significant difference in thermotolerance between the pressurised samples and untreated controls.