HIGH‐PRESSURE DESTRUCTION KINETICS OF SPOILAGE AND PATHOGENIC BACTERIA IN RAW MILK CHEESE

Abstract

ABSTRACT Raw milk cheese samples were individually inoculated with Escherichia coli K‐12, Escherichia coli O157:H7 and Listeria monocytogenes, and subjected to high‐pressure (HP) treatments (200–400 MPa) in both pressure hold and pressure pulse modes. Pressure inactivation of E. coli K‐12 at 350 MPa (5 min) at different temperatures demonstrated a strong temperature effect when temperature was 40C and above. Pressure destruction kinetics and pressure sensitivity were evaluated at 25C (where the temperature effect was minimal). HP treatment generally demonstrated a step‐change pressure pulse effect followed by a holding time destruction that was well described by a first‐order model ( R 2 > 0.90) with higher pressures resulting in a faster rate of microbial reduction (smaller D values). The associated D values at an intermediate pressure of 300 MPa were 4.4, 14.5 and 3.6 min for E. coli K‐12, E. coli O157:H7 and L. monocytogenes, respectively, with E. coli O157:H7 thus demonstrating a higher‐pressure resistance than the other two. The corresponding pressure z p values were 156, 128 and 82 MPa, and Δ V ≠ (Arrhenius volume change of activation) values were − 3.6, − 4.4 and − 7.0 ( × 10 −5 m 3 /mole), respectively. Pulse mode treatments showed similar pressure resistance trends to pressure hold mode, but were not effective for E. coli O157:H7.