Effect of high pressure on destruction kinetics of Escherichia coli (ATCC 25922) in cucumber juice

摘要

Fresh Fresh cucumber juice inoculated with Escherichia coli (ATCC 25922) were subjected to high-pressure treatments (100-600 MPa for 0-20 min) at ambient temperature (25°C) and as well as in inoculated frozen samples. Two different types of culture media, brain heart infusion agar (BHIA) and violet red bile agar (VRBA), were used for enumeration of surviving cells. Kinetic parameters (D, z, Ap and AV± values) were determined based on the first-order rate kinetics and conventional/Arrhenius models.Survivors on BHIA would indicate both injured and pressure resistant spores while survivors on the harsh VRBA would only indicate the pressure resistant survivors. It was observed that at pressure levels 200 MPa or lower E. coli cells were more injured than killed, and with the increase in pressure treatment severity, only the higher pressure resistant fractions survived. For the pressure ranging from 300 to 500 MPa, the decimal reduction pressure increment was Ap=42.2-53.5 MPa. BHIA demonstrated 1.36±0.22 min longer of DPvalue than VRBA, because it included the injured and pressure resistant cells. The E. coli in cucumber juice showed a high Z value (561 MPa for BHIA), meaning a low pressure sensitivity. The E. coli in frozen cucumber juice were moresensitive to pressure destruction than that in the unfrozen juice at ambient temperature.