Inactivation of naturally occurring microbiota in cucumber juice by pressure treatment

The inactivation effects of high hydrostatic pressure (HHP) (350MPa/10min, 400MPa/4min and 500MPa/2min) with homogenization (20MPa/2min), nisin (100IU/mL) and decompression time (<3s and 7-8s) on naturally occurring microbiota in cucumber juice were investigated. Initial concentration of yeasts and molds (Y&M) was 5.6×10(3)-2.4×10(4)CFU/mL, and total plate count (TPC) was 1.0×10(5)-3.5×10(5)CFU/mL. Y&M were inactivated below the detection level (≤10CFU/mL) in all cases. The reduction of TPC in non-homogenized cucumber juice (NHCJ) was 2.5-3.0 log cycles, which was significantly higher than 1.0 log cycle in homogenized cucumber juice. The combination of nisin with HHP had a synergistic effect on the inactivation of TPC. The reduction of TPC in NHCJ with a decompression time of <3s was approximately 4.5 log cycles, which was significantly higher than a decompression time of 7-8s. Five non-linear models including the biphasic, Weibull, modified Gompertz, log-logistic and Baranyi models were fitted to TPC inactivation curves for the NHCJ at 300, 350 and 400MPa for 2-15min and 500MPa for 2-8min at a decompression time of <3s. The biphasic model provided the best fit for the data.