Injury,Inhibition and Inactivation ofEscherichia coli O157:H7 by Potassium Sorbate and Sodium Nitrite as Affected by pH and Temperature

The effect of potassium sorbate (0–2 g litre⁻¹) and sodium nitrite (0–1 g litre⁻¹) on the growth of four strains of Escherichia coli O157: H7 in tryptic soya broth at various pH levels (pH 4·0–7·0 for sorbate, pH 5·0–8·0 for nitrite) were determined at 37°C and 4°C. Among the pH levels tested, sorbate and nitrite exhibited the highest antimicrobial activity at pH 4·0 and 5·0, respectively. At pH 5·0 and 37°C, the presence of 500 mg litre⁻¹ sorbate or 200 mg litre⁻¹ nitrite completely inhibited the growth of E coli O157: H7. While at higher pH levels, 2 g litre⁻¹ sorbate or 1 g litre⁻¹, nitrite, the highest concentration tested, did not show significant antimicrobial action against the test organisms. At 4°C and pH 5·0, the inoculated test organisms did not showed any significant growth in preservative-free control media. Different degree of inactivation and injury was observed when E coli O157: H7 strain 933 was stored in TSB (pH 5·0) containing 1 g litre⁻¹ sorbate or nitrite at 37°C. At 4°C, inactivation and injury of E coli O157: H7 cells was not observed in the medium containing sorbate or nitrite throughout the 24 h experimental period.